Menstrual cycle: Difference between revisions

Content deleted Content added

Inline

Revision as of 00:02, 13 March 2021

The menstrual cycle is a series of natural changes in the uterus and ovaries of the female reproductive system that make pregnancy possible. The ovarian cycle controls the production and release of eggs. The uterine cycle governs the preparation and maintenance of the lining of the uterus (womb) to receive a fertilized egg. These cycles are concurrent and coordinated, and last between 25 and 30 days, with a median length of 28 days.^[1]

Naturally occurring hormones drive the cycles; the cyclical rise and fall of the hormone estrogen prompts the production and growth of oocytes (immature egg cells). The hormone progesterone stimulates the uterus lining to thicken to accommodate an embryo should fertilization occur.^[2] The blood supply of the thickened lining (endometrium) provides nutrients to a successfully implanted embryo. If implantation does not occur, the lining breaks down and blood is released. Triggered by falling progesterone levels, menstruation (a "period", in common parlance) is the cyclical shedding of the lining, and is a sign that pregnancy has not occurred.^[3]

Each cycle occurs in phases based on events in the ovary (ovarian cycle) or the uterus (uterine cycle).^[4] The ovarian cycle consists of the follicular phase, ovulation, and the luteal phase; the uterine cycle consists of the menstrual, proliferative and secretory phases.^[3] Day one of the menstrual cycle is the first day of the period, which lasts for about five days. Around day fourteen, the egg is released from the ovary.^[5] Menarche (the onset of the first period) usually occurs around the age of twelve years.^[6] Menstrual cycles end at menopause, which is usually between 45 and 55 years of age.^[7]

During their menstrual cycle, some women experience problems that disrupt daily life;^[8] such problems can include acne, tender breasts, bloating, tiredness, irritability, and mood changes.^[9] Premenstrual syndrome may affect others and premenstrual dysphoric disorder^[10]^[11] is experienced by 3 to 8% of women.^[1] The menstrual cycle can be modified by hormonal birth control.^[12]

Cycles and phases

The menstrual cycle encompasses the ovarian and uterine cycles. The ovarian cycle describes changes that occur in the follicles of the ovary,^[13] whereas the uterine cycle describes changes in the endometrial lining of the uterus. Both cycles can be divided into phases. The ovarian cycle consists of alternating follicular and luteal phases, and the uterine cycle consists of menstruation, the proliferative phase, and the secretory phase.^[4] The menstrual cycle is controlled by the hypothalamus and the pituitary gland in the brain. The hypothalamus releases gonadotropin releasing hormone (GnRH), which causes the nearby anterior pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Before puberty GnRH is released in steady quantities and at a steady rate. After puberty it is released in large pulses and the frequency and magnitude of these determine how much FSH and LH are produced by the pituitary.^[2]

Measured from the first day of one menstruation to the first day of the next, the length of a menstrual cycle varies.^[1] The cycle is often less regular at the beginning and end of a woman's reproductive life.^[1] Beginning at puberty, a child's body begins to mature into an adult body capable of sexual reproduction; the first period (called menarche) occurs at around 12 years of age.^[6]^[14] The cessation of menstrual cycles at the end of a woman's reproductive period at menopause commonly occurs between the ages of 45 and 55.^[15]

Ovarian cycle

Between menarche and menopause the human ovaries regularly alternate between luteal and follicular phases during the monthly menstrual cycle.^[16] Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood flow stop and the uterus lining thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one, or occasionally two, become dominant, while non-dominant follicles shrink and die. About mid-cycle, some 34–36 hours after the luteinizing hormone (LH) surges,^[1] the dominant follicle releases an oocyte, in an event called ovulation.^[17]

After ovulation, the oocyte lives for 24 hours or less without fertilization,^[18] while the remains of the dominant follicle in the ovary become a corpus luteum—a body with the primary function of producing large amounts of the hormone progesterone.^[19] Under the influence of progesterone, the uterine lining changes to prepare for potential implantation of an embryo to establish a pregnancy. The thickness of the endometrium continues to increase in response to mounting levels of estrogen, which is released by the antral follicle (a mature ovarian follicle) into the blood circulation. Peak levels of estrogen are reached at around day thirteen of the cycle and coincide with ovulation. If implantation does not occur within about two weeks, the corpus luteum degenerates into the corpus albicans, which does not produce hormones, causing a sharp drop in levels of both progesterone and estrogen. This hormone drop causes the uterus to loose its lining in menstruation; it is around this time that the lowest levels of estrogen are reached.^[20]

On average the ovarian cycle lasts about 28 days;^[1]^[16] for most women, cycle lengths are between 25 and 30 days.^[1] Although the average length of the human menstrual cycle is similar to that of the lunar cycle, there is no causal relation between the two.^[21]

Follicular phase

The ovaries contain a finite number of egg stem cells, granulosa cells and theca cells, which together form primordial follicles.^[19] Beginning at puberty, these mature to primary follicles independently of the menstrual cycle.^[22] The follicular phase is the first part of the ovarian cycle and it ends with the completion of the antral follicles.^[16] Meiosis (cell division) remains incomplete in the egg cells until the antral follicle is formed. The development of the egg is called oogenesis and only one cell survives the divisions to await fertilization. The other cells are discarded as polar bodies, which cannot be fertilized.^[23] The follicular phase shortens significantly with age, lasting around 14 days in women aged 18–24 compared with 10 days in women aged 40–44).^[20] During this phase usually only one ovarian follicle fully matures and gets ready to release an egg.^[24]

Through the influence of a rise in follicle stimulating hormone (FSH) during the first days of the cycle, a few ovarian follicles are stimulated. These follicles, which have been developing for the better part of a year in a process known as folliculogenesis, compete with each other for dominance. Under the influence of several hormones, all but one of these follicles will stop growing, while one dominant follicle in the ovary will continue to maturity. The remaining follicles die in a process called follicular atresia.^[25] Luteinising hormone (LH) stimulates further development of the ovarian follicle. The follicle that reaches maturity is called an antral follicle, and it contains the ovum (egg cell).^[2]

The theca cells develop receptors that bind LH, and in response secrete large amounts of androstenedione. At the same time the granulosa cells surrounding the maturing follicle develop receptors that bind FSH, and in response start secreting androstenedione, which is converted to estrogen by the enzyme aromatase. The estrogen inhibits further production of FSH and LH by the pituitary gland. This negative feedback regulates levels of FSH and LH. The dominant follicle continues to secrete estrogen, and the rising estrogen levels make the pituitary more responsive to GnRH from the hypothalamus. As estrogen increases this becomes a positive feedback signal, which makes the pituitary secrete more FSH and LH. This surge of FSH and LH usually occurs one to two days before ovulation, and is responsible for stimulating the rupture of the antral follicle and release of the oocyte.^[22]^[26]

Ovulation

At around 20 weeks gestation some 7 million immature eggs are already formed in an ovary. This decreases to around 2 million by the time a girl is born, and 300,000 by the time she has her first period. On average one egg matures and is released during ovulation each month after menarche.^[27]

Ovulation occurs when a mature egg is released from the ovarian follicles into the fallopian tube about 10 to 12 hours after the peak in LH levels.^[1] Most times only one of the 15–20 follicles that have been stimulated reaches full maturity, and just one egg is released.^[28] Ovulation only occurs in around 10% of cycles during the first two years following menarche, and by the age of 40–50 the number of ovarian follicles is depleted.^[29] Luteinising hormone initiates ovulation at around day 14 and stimulates the formation of the corpus luteum. In turn, and following further stimulation by luteinising hormone, the corpus luteum produces and releases estrogen, progesterone, relaxin (which relaxes the uterus by inhibiting contractions of the myometrium), and inhibin (which inhibits secretion of more luteinising hormone).^[2]

The release of LH matures the egg and weakens the wall of the follicle in the ovary, causing the fully developed follicle to release its oocyte.^[30] If it is fertilized by a sperm, the oocyte promptly matures into an ootid which blocks the other sperm cells and becomes a mature egg. If it is not fertilized by a sperm, the oocyte will degenerate. The mature egg has a diameter of about 0.1 mm (0.0039 in),^[31] and is the largest human cell.^[32]

Which of the two ovaries—left or right—ovulates appears random;^[33] no left and right coordinating process is known.^[34] Occasionally both ovaries will release an egg;^[34] if both eggs are fertilized, the result is fraternal twins.^[35] After release from the ovary, the egg is swept into the fallopian tube by the fimbria—a fringe of tissue at the end of each fallopian tube. After about a day, an unfertilized egg will disintegrate or dissolve in the fallopian tube, and a fertilized egg will reach the uterus in three to five days.^[36]

Fertilization usually takes place in the ampulla, the widest section of the fallopian tubes. A fertilized egg immediately starts the process of embryogenesis (development). The developing embryo takes about three days to reach the uterus, and another three days to implant into the endometrium. It has usually reached the blastocyst stage at the time of implantation: this is when pregnancy begins.^[37] The loss of the corpus luteum is prevented by fertilization of the egg. The syncytiotrophoblast (the outer layer of the resulting embryo-containing blastocyst that later becomes the outer layer of the placenta), produces human chorionic gonadotropin (hCG), which is very similar to LH and which preserves the corpus luteum. The corpus luteum continues to secrete progestoerone and estrogens at levels slightly above those at ovulation during the first few months of pregnancy. After this and for the rest of the pregnancy, the placenta secretes high levels of these hormones along with human chorionic gonadotropin (hCG), which stimulates the corpus luteum to secrete more progesterone and estrogens, blocking the menstrual cycle.^[38] These hormones also prepare the mammary glands for milk^[a] production.^[38]

Luteal phase

Lasting about 14 days,^[1] the luteal phase is the final phase of the ovarian cycle and it corresponds to the secretory phase of the uterine cycle. During the luteal phase, the pituitary hormones FSH and LH cause the remaining parts of the dominant follicle to transform into the corpus luteum, which produces progesterone.^[40] The increased progesterone in the adrenal cortex starts to induce the production of estrogen. The hormones produced by the corpus luteum also suppress production of the FSH and LH that the corpus luteum needs to maintain itself. The level of FSH and LH fall quickly, and the corpus luteum atrophies.^[41] Falling levels of progesterone trigger menstruation and the beginning of the next cycle. From the time of ovulation until progesterone withdrawal has caused menstruation to begin, the process typically takes about two weeks. For an individual woman, the follicular phase often varies in length from cycle to cycle; by contrast, the length of her luteal phase will be fairly consistent from cycle to cycle.^[20] The luteal phase is about the same length in most individuals (average 14 days) whereas the follicular phase tends to show much more variability lasting from 10 to 16 days.^[20]

Uterine cycle

The uterine cycle has three phases: menses, proliferative and secretory.^[42]

Menstruation

Menstruation (also called menstrual bleeding, menses or a period) is the first and most evident phase of the uterine cycle and begins at puberty. Called menarche, the first period occurs at the age of around twelve or thirteen years.^[14] The average age is generally later in the developing world and earlier in developed world.^[43] In precocious puberty, it can occur as early as age eight years,^[44] and this can still be normal.^[45]^[46]

Menstruation is initiated each month by falling levels of estrogen and progesterone and the release of prostaglandins,^[24] which constrict the spiral arteries. This causes them to spasm, contract and break up.^[47] The blood supply to the endometrium is cut off and the cells of the top layer of the endometrium (the stratum functionalis) become deprived of oxygen and die. Later the whole layer is lost and only the bottom layer, the stratum basalis, is left in place.^[24] An enzyme called plasmin breaks up the blood clots in the menstrual fluid, which eases the flow of blood and broken down lining from the uterus.^[48]

The flow of blood normally serves as a sign that a woman has not become pregnant, but this cannot be taken as certainty, as several factors can cause bleeding during pregnancy.^[49] Menstruation occurs on average once a month from menarche to menopause, which corresponds with a woman's fertile years. The average age of menopause in women is 52 years, and it typically occurs between 45 and 55 years of age.^[50]

Eumenorrhea denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal).^[51] The average blood loss during menstruation is 30 milliliters (mL), and more than 80 mL is considered abnormal.^[1] Women who experience menorrhagia (heavy menstrual bleeding) are more susceptible to iron deficiency than the average person.^[52]

Proliferative phase

The proliferative phase is the second phase of the uterine cycle when estrogen causes the lining of the uterus to grow and proliferate.^[41] The latter part of the follicular phase overlaps with the proliferative phase of the uterine cycle.^[33] As they mature, the ovarian follicles secrete increasing amounts of estradiol, an estrogen. The estrogens initiate the formation of a new layer of endometrium in the uterus with the spiral arterioles.^[4]

As estrogen levels increase, cells in the cervix produce a type of cervical mucus^[53] that has a higher pH and is less viscous than usual, rendering it more friendly to sperm.^[54] This increases the chances of fertilization, which occurs around day 11 to day 14.^[18] This cervical mucus can be detected as a vaginal discharge that is copious and resembles raw egg whites.^[55] For women who are practicing fertility awareness, it is a sign that ovulation is about to take place.^[55]

Secretory phase

The secretory phase is the final phase of the uterine cycle and it corresponds to the luteal phase of the ovarian cycle. During the secretory phase, the corpus luteum produces progesterone, which plays a vital role in making the endometrium receptive to the implantation of a blastocyst (a fertilized egg, which has begun to grow).^[56] Glycogen, lipids, and proteins are secreted into the uterus^[57] and the cervical mucus thickens.^[58] In early pregnancy progesterone also increases blood flow and reduces the contractility of the smooth muscle in the uterus^[2] and raises the woman's basal body temperature.^[59]

If pregnancy does not occur the falling levels of estrogen trigger menstruation and the ovarian and uterine cycles start over again.^[48]

Menstrual health

Some women experience problems sufficient to disrupt their lives as a result their menstrual cycle.^[8] These include acne, tender breasts, bloating, feeling tired, irritability mood changes,^[9] and premenstrual syndrome (PMS). More severe problems such as premenstrual dysphoric disorder are experienced by 3 to 8% of women.^[1]^[10] Dysmenorrhea is frequently a source of pelvic pain,^[60] causing cramps in the abdomen, back, or upper thighs that occur during the first few days of menstruation.^[61] These issues can significantly affect a woman's health and quality of life and timely interventions can improve the lives of these women.^[62]

When menstruation begins, symptoms of PMS such as breast tenderness and irritability generally decrease.^[51] In some women, ovulation features a characteristic pain^[b] called mittelschmerz (a German term meaning middle pain).^[51] This occurs when an egg does not enter the fallopian tube but the pelvic cavity where it breaks up. The cause of the pain is the small amount of blood loss associated with the ruptured follicle.^[24]

Even when normal, the changes in hormone levels during the menstrual cycle can increase the incidence of disorders such as autoimmune diseases,^[66] which might be caused by estrogen enhancement of the immune system.^[1]

Hormonal contraception

Hormonal contraceptives prevent pregnancy by inhibiting the secretion of the hormones, FSH, LH and GnRH. Containing estrogen, combined oral contraceptive pills (COCs, often referred to as birth control pills) stop the development of the dominant follicle and the mid-cycle LH surge and thus ovulation.^[67] Another hormone in COCs called progestin stops the cervical mucus from becoming sperm-friendly but does not always prevent ovulation when used alone in progestin-only pills. COCs regulate the length of the menstrual cycle and reduce the amount of blood lost. Hormonal contraception is available in a variety of forms such as pills, patches, skin implants and hormonal intrauterine devices (IUDs).^[68]

Evolution and other species

Most female mammals have an estrous cycle, but only ten primate species, four bat species, the elephant shrew and the spiny mouse have a menstrual cycle.^[69] The cycles are the same as in humans apart from the length, which ranges from 21 to 37 days.^[70] The lack of immediate relationship between these groups suggests that four distinct evolutionary events have caused menstruation to arise.^[71] In species that have a menstrual cycle, ovulation is not obvious to potential mates and there is no mating season.^[72]^[73] There are four theories on the evolutionary significance of menstruation:^[71]

Control of sperm-borne pathogens.^[74]^[75]^[76] This hypothesis held that menstruation protected the uterus against pathogens introduced by sperm. Hypothesis 1 does not take into account that copulation can take place weeks before menstruation and that potentially infectious semen is not controlled by menstruation in other species.^[71]
Energy conservation.^[75]^[77] This hypothesis claimed that it took less energy to rebuild a uterine lining than to maintain it if pregnancy did not occur. Hypothesis 2 does not explain other species that also do not maintain a uterine lining but do not menstruate.^[71]
A theory based on spontaneous decidualization (a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy, in which the endometrium changes into the decidua). Decidualization leads to the development of the endothelium, which involves cells of the immune system,^[70] the formation of a new blood supply, hormones and tissue differentiation. In non-menstruating mammals, decidualization is driven by the embryo, not the mother.^[75] It evolved in some placental mammals because it confers advantages in that it allows females to prepare for pregnancy without needing a signal from the fetus.^[71] Hypothesis 3 defers to an explanation of the evolutionary origin of spontaneous decidualization and does not explain the evolution of menstruation alone.^[71]
Uterine pre-conditioning.^[78] This hypothesis claims that a monthly pre-conditioning of the uterus is needed in species, such as humans, that have deeply invasive (deep-rooted) placentas. In the process leading to the formation of a placenta, maternal tissues are invaded. This hypothesis holds that menstruation was not evolutionary, rather the result of a coincidental pre-conditioning of the uterus to protect uterine tissue from the deeply rooting placenta, in which a thicker endometrium develops.^[78] Hypothesis 4 does not explain menstruation in non-primates.^[71]

Notes

^ Breastfeeding women can experience complete suppression of follicular development, follicular development but no ovulation, or normal menstrual cycles can resume.^[39]
^ Uncharacteristic mid-cycle pain may be caused by medical conditions such as ectopic pregnancy or ruptured ovarian cyst^[63]^[64] or may be confused with appendicitis.^[65]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l Reed BF, Carr BR, Feingold KR, et al. (2018). "The Normal Menstrual Cycle and the Control of Ovulation". Endotext (Review). PMID 25905282.
^ ^a ^b ^c ^d ^e Tortora 2017, p. 942.
^ ^a ^b Draper CF, Duisters K, Weger B, Chakrabarti A, Harms AC, Brennan L, Hankemeier T, Goulet L, Konz T, Martin FP, Moco S, van der Greef J (October 2018). "Menstrual cycle rhythmicity: metabolic patterns in healthy women". Scientific Reports (Journal article). 8 (1): 14568. Bibcode:2018NatSR...814568D. doi:10.1038/s41598-018-32647-0. PMC 6167362. PMID 30275458.
^ ^a ^b ^c Tortora 2017, p. 944.
^ Tortora 2017, p. 943.
^ ^a ^b Lacroix AE, Gondal H, Langaker MD (2020). "Physiology, Menarche". StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing (Review). PMID 29261991.
^ "Menopause: Overview". National Institute of Child Health and Human Development. National Institutes of Health (NIH). 12 January 2016. Retrieved 26 February 2021.
^ ^a ^b Gudipally PR, Sharma GK (2020). Premenstrual syndrome (Review). StatPearls [Internet]. PMID 32809533.
^ ^a ^b "Premenstrual syndrome (PMS) fact sheet". Office of Women's Health. United States Department of Health and Human Services . 23 December 2014. Archived from the original on 28 June 2015. Retrieved 23 June 2015.
^ ^a ^b Appleton SM (March 2018). "Premenstrual syndrome: evidence-based evaluation and treatment". Clinical Obstetrics and Gynecology (Review). 61 (1): 52–61. doi:10.1097/GRF.0000000000000339. PMID 29298169. S2CID 28184066.
^ Biggs WS, Demuth RH (October 2011). "Premenstrual syndrome and premenstrual dysphoric disorder". American Family Physician (Review). 84 (8): 918–24. PMID 22010771.
^ Klump KL, Keel PK, Racine SE, et al. (February 2013). "The interactive effects of estrogen and progesterone on changes in emotional eating across the menstrual cycle". Journal of Abnormal Psychology (Journal article). 122 (1): 131–37. doi:10.1037/a0029524. PMC 3570621. PMID 22889242.
^ Richards JS (2018). "The ovarian cycle". Vitamins and Hormones (Review). 107: 1–25. doi:10.1016/bs.vh.2018.01.009. ISBN 978-0-128-14359-9. PMID 29544627.
^ ^a ^b Papadimitriou A (December 2016). "The evolution of the age at menarche from prehistorical to modern times". Journal of Pediatric and Adolescent Gynecology (Review). 29 (6): 527–30. doi:10.1016/j.jpag.2015.12.002. PMID 26703478.
^ Shadyab AH, Macera CA, Shaffer RA, Jain S, Gallo LC, Gass ML, Waring ME, Stefanick ML, LaCroix AZ (January 2017). "Ages at menarche and menopause and reproductive lifespan as predictors of exceptional longevity in women: the Women's Health Initiative". Menopause (New York, N.Y.) (Journal article). 24 (1): 35–44. doi:10.1097/GME.0000000000000710. PMC 5177476. PMID 27465713.
^ ^a ^b ^c Sherwood 2016, p. 741.
^ Sherwood 2016, p. 747.
^ ^a ^b Tortora 2017, p. 957.
^ ^a ^b Tortora 2017, p. 929.
^ ^a ^b ^c ^d Tortora 2017, pp. 942–46.
^ Norris & Carr 2013, p. 361.
^ ^a ^b Watchman 2020, p. 8.
^ Schmerler S, Wessel GM (January 2011). "Polar bodies – more a lack of understanding than a lack of respect". Molecular Reproduction and Development (Review). 78 (1): 3–8. doi:10.1002/mrd.21266. PMC 3164815. PMID 21268179.
^ ^a ^b ^c ^d Tortora 2017, p. 945.
^ Johnson 2007, p. 86.
^ Sherwood 2016, p. 745.
^ Ugwumadu 2014, p. 115.
^ Sadler 2019, p. 48.
^ Tortora 2017, p. 953.
^ Sherwood 2016, p. 746.
^ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "Eggs". Molecular Biology of the Cell (4th ed.). New York: Garland Science. ISBN 0-8153-3218-1.
^ Iussig B, Maggiulli R, Fabozzi G, Bertelle S, Vaiarelli A, Cimadomo D, Ubaldi FM, Rienzi L (May 2019). "A brief history of oocyte cryopreservation: Arguments and facts". Acta Obstetricia et Gynecologica Scandinavica (Review). 98 (5): 550–58. doi:10.1111/aogs.13569. PMID 30739329.
^ ^a ^b Parker 2019, p. 283.
^ ^a ^b Ecochard R, Gougeon A (April 2000). "Side of ovulation and cycle characteristics in normally fertile women". Human Reproduction (Journal article). 15 (4): 752–55. doi:10.1093/humrep/15.4.752. PMID 10739814.
^ "Multiple Pregnancy: Twins or More — Topic Overview". WebMD Medical Reference from Healthwise. 16 January 2019. Retrieved 26 February 2021.
^ Sadler 2019, p. 36.
^ Tortora 2017, p. 959.
^ ^a ^b Tortora 2017, p. 976.
^ Carr SL, Gaffield ME, Dragoman MV, Phillips S (September 2016). "Safety of the progesterone-releasing vaginal ring (PVR) among lactating women: A systematic review". Contraception (Review). 94 (3): 253–61. doi:10.1016/j.contraception.2015.04.001. PMID 25869631.
^ Johnson 2007, p. 91.
^ ^a ^b Ugwumadu 2014, p. 117.
^ Salamonsen LA (December 2019). "Women in reproductive science: Understanding human endometrial function". Reproduction (Cambridge, England) (Review). 158 (6): F55–F67. doi:10.1530/REP-18-0518. PMID 30521482.
^ Alvergne A, Högqvist Tabor V (June 2018). "Is female health cyclical? Evolutionary perspectives on menstruation". Trends in Ecology & Evolution (Review). 33 (6): 399–414. arXiv:1704.08590. doi:10.1016/j.tree.2018.03.006. PMID 29778270. S2CID 4581833.
^ Ibitoye M, Choi C, Tai H, Lee G, Sommer M (2017). "Early menarche: A systematic review of its effect on sexual and reproductive health in low- and middle-income countries". PLOS ONE (Review). 12 (6): e0178884. Bibcode:2017PLoSO..1278884I. doi:10.1371/journal.pone.0178884. PMC 5462398. PMID 28591132.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ "Menstruation and the menstrual cycle fact sheet". Office of Women's Health. US Department of Health and Human Services. 23 December 2014. Archived from the original on 26 June 2015. Retrieved 25 June 2015.
^ Sultan C, Gaspari L, Maimoun L, Kalfa N, Paris F (April 2018). "Disorders of puberty" (PDF). Best Practice & Research. Clinical Obstetrics & Gynaecology (Review). 48: 62–89. doi:10.1016/j.bpobgyn.2017.11.004. PMID 29422239.
^ Johnson 2007, pp. 152.
^ ^a ^b Tortora 2017, p. 600.
^ Breeze C (May 2016). "Early pregnancy bleeding". Australian Family Physician (Review). 45 (5): 283–86. PMID 27166462.
^ Towner MC, Nenko I, Walton SE (April 2016). "Why do women stop reproducing before menopause? A life-history approach to age at last birth". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences (Review). 371 (1692): 20150147. doi:10.1098/rstb.2015.0147. PMC 4822427. PMID 27022074.
^ ^a ^b ^c Goldenring JM (1 February 2019). "All About Menstruation". WebMD. Retrieved 26 February 2021.
^ Harvey LJ, Armah CN, Dainty JR, Foxall RJ, John Lewis D, Langford NJ, Fairweather-Tait SJ (October 2005). "Impact of menstrual blood loss and diet on iron deficiency among women in the UK". The British Journal of Nutrition (Comparative study). 94 (4): 557–64. doi:10.1079/BJN20051493. PMID 16197581.
^ Simmons RG, Jennings V (July 2020). "Fertility awareness-based methods of family planning". Best Practice & Research. Clinical Obstetrics & Gynaecology (Review). 66: 68–82. doi:10.1016/j.bpobgyn.2019.12.003. PMID 32169418.
^ Tortora 2017, pp. 936–37.
^ ^a ^b Su HW, Yi YC, Wei TY, Chang TC, Cheng CM (September 2017). "Detection of ovulation, a review of currently available methods". Bioeng Transl Med (Review). 2 (3): 238–246. doi:10.1002/btm2.10058. PMC 5689497. PMID 29313033.
^ Lessey BA, Young SL (April 2019). "What exactly is endometrial receptivity?". Fertility and Sterility (Review). 111 (4): 611–17. doi:10.1016/j.fertnstert.2019.02.009. PMID 30929718.
^ Salamonsen LA, Evans J, Nguyen HP, Edgell TA (March 2016). "The microenvironment of human implantation: determinant of reproductive success". American Journal of Reproductive Immunology (New York, N.Y. : 1989) (Review). 75 (3): 218–25. doi:10.1111/aji.12450. PMID 26661899.
^ Han L, Taub R, Jensen JT (November 2017). "Cervical mucus and contraception: what we know and what we don't". Contraception (Review). 96 (5): 310–321. doi:10.1016/j.contraception.2017.07.168. PMID 28801053.
^ Charkoudian N, Hart EC, Barnes JN, Joyner MJ (June 2017). "Autonomic control of body temperature and blood pressure: influences of female sex hormones" (PDF). Clinical Autonomic Research (Review). 27 (3): 149–55. doi:10.1007/s10286-017-0420-z. PMID 28488202. S2CID 3773043.
^ Nagy H, Khan MA (2020). "Dysmenorrhea". StatPearls (Review). PMID 32809669.
^ Baker FC, Lee KA (September 2018). "Menstrual cycle effects on sleep". Sleep Medicine Clinics (Review). 13 (3): 283–94. doi:10.1016/j.jsmc.2018.04.002. PMID 30098748.
^ Matteson KA, Zaluski KM (September 2019). "Menstrual health as a part of preventive health care". Obstetrics and Gynecology Clinics of North America (Review). 46 (3): 441–53. doi:10.1016/j.ogc.2019.04.004. PMID 31378287.
^ Kruszka PS, Kruszka SJ (July 2010). "Evaluation of acute pelvic pain in women". Am Fam Physician (Review). 82 (2): 141–47. PMID 20642266.
^ Cleary M, Flanagan KW (2019). Acute and Emergency Care in Athletic Training. Human Kinetics. p. 340.
^ Brott NR, Le JK (2020). "Mittelschmerz". Stat Pearls [Internet] (Review). PMID 31747229.
^ Talsania M, Scofield RH (May 2017). "Menopause and rheumatic disease". Rheumatic Diseases Clinics of North America (Review). 43 (2): 287–302. doi:10.1016/j.rdc.2016.12.011. PMC 5385852. PMID 28390570.
^ Tortora 2017, p. 948.
^ Tortora 2017, pp. 948–49.
^ Bellofiore N, Ellery SJ, Mamrot J, Walker DW, Temple-Smith P, Dickinson H (January 2017). "First evidence of a menstruating rodent: the spiny mouse (Acomys cahirinus)". American Journal of Obstetrics and Gynecology (Journal article). 216 (1): 40.e1–40.e11. doi:10.1016/j.ajog.2016.07.041. PMID 27503621. S2CID 88779.
^ ^a ^b Catalini L, Fedder J (May 2020). "Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom†". Biology of Reproduction (Journal article). 102 (6): 1160–1169. doi:10.1093/biolre/ioaa029. PMC 7253787. PMID 32129461.
^ ^a ^b ^c ^d ^e ^f ^g Emera D, Romero R, Wagner G (January 2012). "The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness". BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology (Journal article). 34 (1): 26–35. doi:10.1002/bies.201100099. PMC 3528014. PMID 22057551. {{cite journal}}: Unknown parameter |lay-date= ignored (help); Unknown parameter |lay-source= ignored (help); Unknown parameter |lay-url= ignored (help)
^ Schjenken JE, Robertson SA (July 2020). "The female response to seminal fluid". Physiological Reviews (Review). 100 (3): 1077–117. doi:10.1152/physrev.00013.2018. PMID 31999507.
^ Muller MN (May 2017). "Testosterone and reproductive effort in male primates". Hormones and Behavior (Review). 91: 36–51. doi:10.1016/j.yhbeh.2016.09.001. PMC 5342957. PMID 27616559.
^ Martin RD (2007). "The evolution of human reproduction: a primatological perspective". American Journal of Physical Anthropology (Review). Suppl 45: 59–84. doi:10.1002/ajpa.20734. PMID 18046752.
^ ^a ^b ^c Finn CA (June 1998). "Menstruation: a nonadaptive consequence of uterine evolution". The Quarterly Review of Biology (Review). 73 (2): 163–73. doi:10.1086/420183. PMID 9618925. S2CID 25135630.
^ Profet M (September 1993). "Menstruation as a defense against pathogens transported by sperm". The Quarterly Review of Biology (Review). 68 (3): 335–86. doi:10.1086/418170. PMID 8210311. S2CID 23738569.
^ Strassmann BI (June 1996). "The evolution of endometrial cycles and menstruation". The Quarterly Review of Biology (Review). 71 (2): 181–220. doi:10.1086/419369. PMID 8693059. S2CID 6207295.
^ ^a ^b Brosens JJ, Parker MG, McIndoe A, Pijnenborg R, Brosens IA (June 2009). "A role for menstruation in preconditioning the uterus for successful pregnancy". American Journal of Obstetrics and Gynecology (Journal article). 200 (6): 615.e1–6. doi:10.1016/j.ajog.2008.11.037. PMID 19136085.

Book sources

Johnson MH (2007). Essential Reproduction. Malden, Massachusetts: Blackwell Publishing. ISBN 978-1-4051-1866-8. OCLC 76074156.
Norris DA, Carr JA (2013). Vertebrate Endocrinology (5th ed.). Academic Press. ISBN 978-0-123-96465-6.
Parker S (2019). The Concise Human Body Book: An Illustrated Guide to its Structures, Function and Disorders. London: Dorling Kindersley. ISBN 978-0-241-39552-3. OCLC 1091644711.
Sadler TW (2019). Langman's Medical Embryology. Philadelphia: Wolters Kluwer. ISBN 978-1-4963-8390-7. OCLC 1042400100.
Sherwood L (2016). Human Physiology: From Cells to Systems. Boston, MA, USA: Cengage Learning. ISBN 978-1-285-86693-2. OCLC 905848832.
Tortora G (2017). Tortora's Principles of Anatomy & Physiology. Hoboken, NJ: John Wiley & Sons, Inc. ISBN 978-1-119-38292-8. OCLC 990424568.
Ugwumadu A (2014). Basic Sciences for Obstetrics and Gynaecology: Core Material for MRCOG. Oxford, England: Oxford University Press. ISBN 978-0-19-953508-8. OCLC 889303297.
Watchman T (2020). Zero to Finals : Obstetrics and Gynaecology. Manchester: Zero to Finals. ISBN 979-8-6037-9726-7. OCLC 1233034578.

External links

Media related to Menstrual cycle at Wikimedia Commons

[40] Breastfeeding women can experience complete suppression of follicular development, follicular development but no ovulation, or normal menstrual cycles can resume.^[39]

[67] Uncharacteristic mid-cycle pain may be caused by medical conditions such as ectopic pregnancy or ruptured ovarian cyst^[63]^[64] or may be confused with appendicitis.^[65]

[Reed2018-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l Reed BF, Carr BR, Feingold KR, et al. (2018). "The Normal Menstrual Cycle and the Control of Ovulation". Endotext (Review). PMID 25905282.

[FOOTNOTETortora2017942-2] Tortora 2017, p. 942.

[pmid30275458-3] Draper CF, Duisters K, Weger B, Chakrabarti A, Harms AC, Brennan L, Hankemeier T, Goulet L, Konz T, Martin FP, Moco S, van der Greef J (October 2018). "Menstrual cycle rhythmicity: metabolic patterns in healthy women". Scientific Reports (Journal article). 8 (1): 14568. Bibcode:2018NatSR...814568D. doi:10.1038/s41598-018-32647-0. PMC 6167362. PMID 30275458.

[FOOTNOTETortora2017944-4] Tortora 2017, p. 944.

[FOOTNOTETortora2017943-5] Tortora 2017, p. 943.

[pmid29261991-6] Lacroix AE, Gondal H, Langaker MD (2020). "Physiology, Menarche". StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing (Review). PMID 29261991.

[NIH2013Def-7] "Menopause: Overview". National Institute of Child Health and Human Development. National Institutes of Health (NIH). 12 January 2016. Retrieved 26 February 2021.

[pmid32809533-8] Gudipally PR, Sharma GK (2020). Premenstrual syndrome (Review). StatPearls [Internet]. PMID 32809533.

[Women2014PMS-9] "Premenstrual syndrome (PMS) fact sheet". Office of Women's Health. United States Department of Health and Human Services . 23 December 2014. Archived from the original on 28 June 2015. Retrieved 23 June 2015.

[pmid29298169-10] Appleton SM (March 2018). "Premenstrual syndrome: evidence-based evaluation and treatment". Clinical Obstetrics and Gynecology (Review). 61 (1): 52–61. doi:10.1097/GRF.0000000000000339. PMID 29298169. S2CID 28184066.

[AFP2011-11] Biggs WS, Demuth RH (October 2011). "Premenstrual syndrome and premenstrual dysphoric disorder". American Family Physician (Review). 84 (8): 918–24. PMID 22010771.

[12] Klump KL, Keel PK, Racine SE, et al. (February 2013). "The interactive effects of estrogen and progesterone on changes in emotional eating across the menstrual cycle". Journal of Abnormal Psychology (Journal article). 122 (1): 131–37. doi:10.1037/a0029524. PMC 3570621. PMID 22889242.

[pmid29544627-13] Richards JS (2018). "The ovarian cycle". Vitamins and Hormones (Review). 107: 1–25. doi:10.1016/bs.vh.2018.01.009. ISBN 978-0-128-14359-9. PMID 29544627.

[pmid26703478-14] Papadimitriou A (December 2016). "The evolution of the age at menarche from prehistorical to modern times". Journal of Pediatric and Adolescent Gynecology (Review). 29 (6): 527–30. doi:10.1016/j.jpag.2015.12.002. PMID 26703478.

[pmid27465713-15] Shadyab AH, Macera CA, Shaffer RA, Jain S, Gallo LC, Gass ML, Waring ME, Stefanick ML, LaCroix AZ (January 2017). "Ages at menarche and menopause and reproductive lifespan as predictors of exceptional longevity in women: the Women's Health Initiative". Menopause (New York, N.Y.) (Journal article). 24 (1): 35–44. doi:10.1097/GME.0000000000000710. PMC 5177476. PMID 27465713.

[FOOTNOTESherwood2016741-16] Sherwood 2016, p. 741.

[FOOTNOTESherwood2016747-17] Sherwood 2016, p. 747.

[FOOTNOTETortora2017957-18] Tortora 2017, p. 957.

[FOOTNOTETortora2017929-19] Tortora 2017, p. 929.

[FOOTNOTETortora2017942–46-20] Tortora 2017, pp. 942–46.

[FOOTNOTENorrisCarr2013[httpsbooksgooglecombooksidF_NaW1ZcSSACpgPA361_361]-21] Norris & Carr 2013, p. 361.

[FOOTNOTEWatchman20208-22] Watchman 2020, p. 8.

[pmid21268179-23] Schmerler S, Wessel GM (January 2011). "Polar bodies – more a lack of understanding than a lack of respect". Molecular Reproduction and Development (Review). 78 (1): 3–8. doi:10.1002/mrd.21266. PMC 3164815. PMID 21268179.

[FOOTNOTETortora2017945-24] Tortora 2017, p. 945.

[FOOTNOTEJohnson200786-25] Johnson 2007, p. 86.

[FOOTNOTESherwood2016745-26] Sherwood 2016, p. 745.

[FOOTNOTEUgwumadu2014115-27] Ugwumadu 2014, p. 115.

[FOOTNOTESadler201948-28] Sadler 2019, p. 48.

[FOOTNOTETortora2017953-29] Tortora 2017, p. 953.

[FOOTNOTESherwood2016746-30] Sherwood 2016, p. 746.

[31] Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "Eggs". Molecular Biology of the Cell (4th ed.). New York: Garland Science. ISBN 0-8153-3218-1.

[pmid30739329-32] Iussig B, Maggiulli R, Fabozzi G, Bertelle S, Vaiarelli A, Cimadomo D, Ubaldi FM, Rienzi L (May 2019). "A brief history of oocyte cryopreservation: Arguments and facts". Acta Obstetricia et Gynecologica Scandinavica (Review). 98 (5): 550–58. doi:10.1111/aogs.13569. PMID 30739329.

[FOOTNOTEParker2019283-33] Parker 2019, p. 283.

[ov-34] Ecochard R, Gougeon A (April 2000). "Side of ovulation and cycle characteristics in normally fertile women". Human Reproduction (Journal article). 15 (4): 752–55. doi:10.1093/humrep/15.4.752. PMID 10739814.

[twins-35] "Multiple Pregnancy: Twins or More — Topic Overview". WebMD Medical Reference from Healthwise. 16 January 2019. Retrieved 26 February 2021.

[FOOTNOTESadler201936-36] Sadler 2019, p. 36.

[FOOTNOTETortora2017959-37] Tortora 2017, p. 959.

[FOOTNOTETortora2017976-38] Tortora 2017, p. 976.

[pmid25869631-39] Carr SL, Gaffield ME, Dragoman MV, Phillips S (September 2016). "Safety of the progesterone-releasing vaginal ring (PVR) among lactating women: A systematic review". Contraception (Review). 94 (3): 253–61. doi:10.1016/j.contraception.2015.04.001. PMID 25869631.

[FOOTNOTEJohnson200791-41] Johnson 2007, p. 91.

[FOOTNOTEUgwumadu2014117-42] Ugwumadu 2014, p. 117.

[pmid30521482-43] Salamonsen LA (December 2019). "Women in reproductive science: Understanding human endometrial function". Reproduction (Cambridge, England) (Review). 158 (6): F55–F67. doi:10.1530/REP-18-0518. PMID 30521482.

[pmid29778270-44] Alvergne A, Högqvist Tabor V (June 2018). "Is female health cyclical? Evolutionary perspectives on menstruation". Trends in Ecology & Evolution (Review). 33 (6): 399–414. arXiv:1704.08590. doi:10.1016/j.tree.2018.03.006. PMID 29778270. S2CID 4581833.

[pmid28591132-45] Ibitoye M, Choi C, Tai H, Lee G, Sommer M (2017). "Early menarche: A systematic review of its effect on sexual and reproductive health in low- and middle-income countries". PLOS ONE (Review). 12 (6): e0178884. Bibcode:2017PLoSO..1278884I. doi:10.1371/journal.pone.0178884. PMC 5462398. PMID 28591132.{{cite journal}}: CS1 maint: unflagged free DOI (link)

[Women2014Men-46] "Menstruation and the menstrual cycle fact sheet". Office of Women's Health. US Department of Health and Human Services. 23 December 2014. Archived from the original on 26 June 2015. Retrieved 25 June 2015.

[pmid29422239-47] Sultan C, Gaspari L, Maimoun L, Kalfa N, Paris F (April 2018). "Disorders of puberty" (PDF). Best Practice & Research. Clinical Obstetrics & Gynaecology (Review). 48: 62–89. doi:10.1016/j.bpobgyn.2017.11.004. PMID 29422239.

[FOOTNOTEJohnson2007152-48] Johnson 2007, pp. 152.

[FOOTNOTETortora2017600-49] Tortora 2017, p. 600.

[pmid27166462-50] Breeze C (May 2016). "Early pregnancy bleeding". Australian Family Physician (Review). 45 (5): 283–86. PMID 27166462.

[pmid27022074-51] Towner MC, Nenko I, Walton SE (April 2016). "Why do women stop reproducing before menopause? A life-history approach to age at last birth". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences (Review). 371 (1692): 20150147. doi:10.1098/rstb.2015.0147. PMC 4822427. PMID 27022074.

[allmenses-52] Goldenring JM (1 February 2019). "All About Menstruation". WebMD. Retrieved 26 February 2021.

[iron-53] Harvey LJ, Armah CN, Dainty JR, Foxall RJ, John Lewis D, Langford NJ, Fairweather-Tait SJ (October 2005). "Impact of menstrual blood loss and diet on iron deficiency among women in the UK". The British Journal of Nutrition (Comparative study). 94 (4): 557–64. doi:10.1079/BJN20051493. PMID 16197581.

[54] Simmons RG, Jennings V (July 2020). "Fertility awareness-based methods of family planning". Best Practice & Research. Clinical Obstetrics & Gynaecology (Review). 66: 68–82. doi:10.1016/j.bpobgyn.2019.12.003. PMID 32169418.

[FOOTNOTETortora2017936–37-55] Tortora 2017, pp. 936–37.

[Su2017-56] Su HW, Yi YC, Wei TY, Chang TC, Cheng CM (September 2017). "Detection of ovulation, a review of currently available methods". Bioeng Transl Med (Review). 2 (3): 238–246. doi:10.1002/btm2.10058. PMC 5689497. PMID 29313033.

[pmid30929718-57] Lessey BA, Young SL (April 2019). "What exactly is endometrial receptivity?". Fertility and Sterility (Review). 111 (4): 611–17. doi:10.1016/j.fertnstert.2019.02.009. PMID 30929718.

[pmid26661899-58] Salamonsen LA, Evans J, Nguyen HP, Edgell TA (March 2016). "The microenvironment of human implantation: determinant of reproductive success". American Journal of Reproductive Immunology (New York, N.Y. : 1989) (Review). 75 (3): 218–25. doi:10.1111/aji.12450. PMID 26661899.

[pmid28801053-59] Han L, Taub R, Jensen JT (November 2017). "Cervical mucus and contraception: what we know and what we don't". Contraception (Review). 96 (5): 310–321. doi:10.1016/j.contraception.2017.07.168. PMID 28801053.

[pmid28488202-60] Charkoudian N, Hart EC, Barnes JN, Joyner MJ (June 2017). "Autonomic control of body temperature and blood pressure: influences of female sex hormones" (PDF). Clinical Autonomic Research (Review). 27 (3): 149–55. doi:10.1007/s10286-017-0420-z. PMID 28488202. S2CID 3773043.

[Dysmenorrheastat-61] Nagy H, Khan MA (2020). "Dysmenorrhea". StatPearls (Review). PMID 32809669.

[pmid30098748-62] Baker FC, Lee KA (September 2018). "Menstrual cycle effects on sleep". Sleep Medicine Clinics (Review). 13 (3): 283–94. doi:10.1016/j.jsmc.2018.04.002. PMID 30098748.

[pmid31378287-63] Matteson KA, Zaluski KM (September 2019). "Menstrual health as a part of preventive health care". Obstetrics and Gynecology Clinics of North America (Review). 46 (3): 441–53. doi:10.1016/j.ogc.2019.04.004. PMID 31378287.

[64] Kruszka PS, Kruszka SJ (July 2010). "Evaluation of acute pelvic pain in women". Am Fam Physician (Review). 82 (2): 141–47. PMID 20642266.

[65] Cleary M, Flanagan KW (2019). Acute and Emergency Care in Athletic Training. Human Kinetics. p. 340.

[66] Brott NR, Le JK (2020). "Mittelschmerz". Stat Pearls [Internet] (Review). PMID 31747229.

[pmid28390570-68] Talsania M, Scofield RH (May 2017). "Menopause and rheumatic disease". Rheumatic Diseases Clinics of North America (Review). 43 (2): 287–302. doi:10.1016/j.rdc.2016.12.011. PMC 5385852. PMID 28390570.

[FOOTNOTETortora2017948-69] Tortora 2017, p. 948.

[FOOTNOTETortora2017948–49-70] Tortora 2017, pp. 948–49.

[71] Bellofiore N, Ellery SJ, Mamrot J, Walker DW, Temple-Smith P, Dickinson H (January 2017). "First evidence of a menstruating rodent: the spiny mouse (Acomys cahirinus)". American Journal of Obstetrics and Gynecology (Journal article). 216 (1): 40.e1–40.e11. doi:10.1016/j.ajog.2016.07.041. PMID 27503621. S2CID 88779.

[pmid32129461-72] Catalini L, Fedder J (May 2020). "Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom†". Biology of Reproduction (Journal article). 102 (6): 1160–1169. doi:10.1093/biolre/ioaa029. PMC 7253787. PMID 32129461.

[Emera2012-73] ^ ^a ^b ^c ^d ^e ^f ^g Emera D, Romero R, Wagner G (January 2012). "The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness". BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology (Journal article). 34 (1): 26–35. doi:10.1002/bies.201100099. PMC 3528014. PMID 22057551. {{cite journal}}: Unknown parameter |lay-date= ignored (help); Unknown parameter |lay-source= ignored (help); Unknown parameter |lay-url= ignored (help)

[pmid31999507-74] Schjenken JE, Robertson SA (July 2020). "The female response to seminal fluid". Physiological Reviews (Review). 100 (3): 1077–117. doi:10.1152/physrev.00013.2018. PMID 31999507.

[pmid27616559-75] Muller MN (May 2017). "Testosterone and reproductive effort in male primates". Hormones and Behavior (Review). 91: 36–51. doi:10.1016/j.yhbeh.2016.09.001. PMC 5342957. PMID 27616559.

[pmid18046752-76] Martin RD (2007). "The evolution of human reproduction: a primatological perspective". American Journal of Physical Anthropology (Review). Suppl 45: 59–84. doi:10.1002/ajpa.20734. PMID 18046752.

[pmid9618925-77] Finn CA (June 1998). "Menstruation: a nonadaptive consequence of uterine evolution". The Quarterly Review of Biology (Review). 73 (2): 163–73. doi:10.1086/420183. PMID 9618925. S2CID 25135630.

[pmid8210311-78] Profet M (September 1993). "Menstruation as a defense against pathogens transported by sperm". The Quarterly Review of Biology (Review). 68 (3): 335–86. doi:10.1086/418170. PMID 8210311. S2CID 23738569.

[pmid8693059-79] Strassmann BI (June 1996). "The evolution of endometrial cycles and menstruation". The Quarterly Review of Biology (Review). 71 (2): 181–220. doi:10.1086/419369. PMID 8693059. S2CID 6207295.

[pmid19136085-80] Brosens JJ, Parker MG, McIndoe A, Pijnenborg R, Brosens IA (June 2009). "A role for menstruation in preconditioning the uterus for successful pregnancy". American Journal of Obstetrics and Gynecology (Journal article). 200 (6): 615.e1–6. doi:10.1016/j.ajog.2008.11.037. PMID 19136085.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[a]

[40]

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55]

[56]

[57]

[58]

[59]

[60]

[61]

[62]

[b]

[66]

[67]

[68]

[69]

[70]

[71]

[72]

[73]

[74]

[75]

[76]

[77]

[78]

[39]

[63]

[64]

[65]

@@ Line 5: / Line 5: @@
 The '''menstrual cycle''' is a series of natural changes in the [[uterus]] and [[ovaries]] of the [[female reproductive system]] that make [[pregnancy]] possible. The ovarian cycle controls the production and release of eggs. The uterine cycle governs the preparation and maintenance of the lining of the uterus (womb) to receive a [[fertilization|fertilized]] egg. These cycles are concurrent and coordinated, and last between 25 and 30 days, with a [[median]] length of 28 days.<ref name="Reed2018" />
-Naturally occurring [[hormones]] drive the cycles; the cyclical rise and fall of the hormone [[estrogen]] prompts the production and growth of [[oocyte]]s (immature egg cells). The hormone [[progesterone]] stimulates the uterus lining to thicken to accommodate an [[embryo]] should fertilization occur.{{sfn | Tortora | 2017 | p=942}} The blood supply of the thickened lining ([[endometrium]]) provides [[nutrient]]s to a successfully [[Implantation (human embryo)|implanted]] embryo. If implantation does not occur, the lining breaks down and blood is released. Triggered by falling progesterone levels, [[menstruation]] (a "period", in common parlance) is the cyclical shedding of the lining, and is a sign that pregnancy has not occurred.<ref name="pmid30275458">{{cite journal |vauthors=Draper CF, Duisters K, Weger B, Chakrabarti A, Harms AC, Brennan L, Hankemeier T, Goulet L, Konz T, Martin FP, Moco S, van der Greef J |title=Menstrual cycle rhythmicity: metabolic patterns in healthy women |journal=Scientific Reports |volume=8 |issue=1 |pages=14568 |date=October 2018 |pmid=30275458 |pmc=6167362 |doi=10.1038/s41598-018-32647-0 |bibcode=2018NatSR...814568D}}</ref>
+Naturally occurring [[hormones]] drive the cycles; the cyclical rise and fall of the hormone [[estrogen]] prompts the production and growth of [[oocyte]]s (immature egg cells). The hormone [[progesterone]] stimulates the uterus lining to thicken to accommodate an [[embryo]] should fertilization occur.{{sfn | Tortora | 2017 | p=942}} The blood supply of the thickened lining ([[endometrium]]) provides [[nutrient]]s to a successfully [[Implantation (human embryo)|implanted]] embryo. If implantation does not occur, the lining breaks down and blood is released. Triggered by falling progesterone levels, [[menstruation]] (a "period", in common parlance) is the cyclical shedding of the lining, and is a sign that pregnancy has not occurred.<ref name="pmid30275458">{{cite journal |vauthors=Draper CF, Duisters K, Weger B, Chakrabarti A, Harms AC, Brennan L, Hankemeier T, Goulet L, Konz T, Martin FP, Moco S, van der Greef J |title=Menstrual cycle rhythmicity: metabolic patterns in healthy women |journal=Scientific Reports |volume=8 |issue=1 |pages=14568 |date=October 2018 |pmid=30275458 |pmc=6167362 |doi=10.1038/s41598-018-32647-0 |bibcode=2018NatSR...814568D|type= Journal article}}</ref>
-Each cycle occurs in phases based on events in the ovary (ovarian cycle) or the uterus (uterine cycle).{{sfn | Tortora | 2017 | p=944}} The ovarian cycle consists of the [[follicular phase]], [[ovulation]], and the [[luteal phase]]; the uterine cycle consists of the menstrual, proliferative and secretory phases.<ref name="pmid30275458"/> Day one of the menstrual cycle is the first day of the period, which lasts for about five days. Around day fourteen, the egg is released from the ovary.{{sfn | Tortora | 2017 | p=943}} [[Menarche]] (the onset of the first period) usually occurs around the age of twelve years.<ref name="pmid29261991">{{cite journal |vauthors=Lacroix AE, Gondal H, Langaker MD |title=Physiology, Menarche |journal=StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing |year=2020 |pmid=29261991 }}</ref> Menstrual cycles end at [[menopause]], which is usually between 45 and 55 years of age.<ref name=NIH2013Def>{{cite web|title=Menopause: Overview|url=http://www.nichd.nih.gov/health/topics/menopause/Pages/default.aspx|work= National Institute of Child Health and Human Development |publisher=[[National Institutes of Health]] (NIH)|date=12 January 2016|access-date=26 February 2021}}</ref>
+Each cycle occurs in phases based on events in the ovary (ovarian cycle) or the uterus (uterine cycle).{{sfn | Tortora | 2017 | p=944}} The ovarian cycle consists of the [[follicular phase]], [[ovulation]], and the [[luteal phase]]; the uterine cycle consists of the menstrual, proliferative and secretory phases.<ref name="pmid30275458"/> Day one of the menstrual cycle is the first day of the period, which lasts for about five days. Around day fourteen, the egg is released from the ovary.{{sfn | Tortora | 2017 | p=943}} [[Menarche]] (the onset of the first period) usually occurs around the age of twelve years.<ref name="pmid29261991">{{cite journal |vauthors=Lacroix AE, Gondal H, Langaker MD |title=Physiology, Menarche |journal=StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing |year=2020 |pmid=29261991|type= Review }}</ref> Menstrual cycles end at [[menopause]], which is usually between 45 and 55 years of age.<ref name=NIH2013Def>{{cite web|title=Menopause: Overview|url=http://www.nichd.nih.gov/health/topics/menopause/Pages/default.aspx|work= National Institute of Child Health and Human Development |publisher=[[National Institutes of Health]] (NIH)|date=12 January 2016|access-date=26 February 2021}}</ref>
-During their menstrual cycle, some women experience problems that disrupt daily life;<ref name="pmid32809533" /> such problems can include [[acne vulgaris|acne]], tender breasts, bloating, tiredness, irritability, and mood changes.<ref name="Women2014PMS">{{cite web|title=Premenstrual syndrome (PMS) fact sheet|url=http://www.womenshealth.gov/publications/our-publications/fact-sheet/premenstrual-syndrome.html|website=Office of Women's Health |publisher= [[United States Department of Health and Human Services ]] |access-date=23 June 2015|date=23 December 2014|url-status=dead|archive-url=https://web.archive.org/web/20150628073755/http://www.womenshealth.gov/publications/our-publications/fact-sheet/premenstrual-syndrome.html |archive-date=28 June 2015}}</ref>  [[Premenstrual syndrome]] may affect others and [[premenstrual dysphoric disorder]]<ref name="pmid29298169" /><ref name="AFP2011">{{cite journal | vauthors = Biggs WS, Demuth RH | title = Premenstrual syndrome and premenstrual dysphoric disorder | journal = American Family Physician | volume = 84 | issue = 8 | pages = 918–24 | date = October 2011 | pmid = 22010771 }}</ref> is experienced by 3 to 8% of women.<ref name="Reed2018" /> The menstrual cycle can be modified by [[hormonal birth control]].<ref>{{cite journal | vauthors = Klump KL, Keel PK, Racine SE, Burt SA, Burt AS, Neale M, Sisk CL, Boker S, Hu JY | display-authors = 3 | title = The interactive effects of estrogen and progesterone on changes in emotional eating across the menstrual cycle | journal = Journal of Abnormal Psychology | volume = 122 | issue = 1 | pages = 131–37 | date = February 2013 | pmid = 22889242 | pmc = 3570621 | doi = 10.1037/a0029524 }}</ref>
+During their menstrual cycle, some women experience problems that disrupt daily life;<ref name="pmid32809533" /> such problems can include [[acne vulgaris|acne]], tender breasts, bloating, tiredness, irritability, and mood changes.<ref name="Women2014PMS">{{cite web|title=Premenstrual syndrome (PMS) fact sheet|url=http://www.womenshealth.gov/publications/our-publications/fact-sheet/premenstrual-syndrome.html|website=Office of Women's Health |publisher= [[United States Department of Health and Human Services ]] |access-date=23 June 2015|date=23 December 2014|url-status=dead|archive-url=https://web.archive.org/web/20150628073755/http://www.womenshealth.gov/publications/our-publications/fact-sheet/premenstrual-syndrome.html |archive-date=28 June 2015}}</ref>  [[Premenstrual syndrome]] may affect others and [[premenstrual dysphoric disorder]]<ref name="pmid29298169" /><ref name="AFP2011">{{cite journal | vauthors = Biggs WS, Demuth RH | title = Premenstrual syndrome and premenstrual dysphoric disorder | journal = American Family Physician | volume = 84 | issue = 8 | pages = 918–24 | date = October 2011 | pmid = 22010771 |type= Review}}</ref> is experienced by 3 to 8% of women.<ref name="Reed2018" /> The menstrual cycle can be modified by [[hormonal birth control]].<ref>{{cite journal | vauthors = Klump KL, Keel PK, Racine SE, Burt SA, Burt AS, Neale M, Sisk CL, Boker S, Hu JY | display-authors = 3 | title = The interactive effects of estrogen and progesterone on changes in emotional eating across the menstrual cycle | journal = Journal of Abnormal Psychology | volume = 122 | issue = 1 | pages = 131–37 | date = February 2013 | pmid = 22889242 | pmc = 3570621 | doi = 10.1037/a0029524 |type= Journal article}}</ref>
 == Cycles and phases ==
 [[File:Figure 28 02 07.jpg|thumb|upright=1.5|right|The progression of the menstrual cycle and the different hormones contributing to it]]
-The menstrual cycle encompasses the ovarian and uterine cycles. The ovarian cycle describes changes that occur in the [[Ovarian follicle|follicles]] of the [[ovary]],<ref name="pmid29544627">{{cite journal|vauthors=Richards JS|date=2018|title=The Ovarian Cycle|journal=Vitamins and Hormones|volume=107|issue=|pages=1–25|doi=10.1016/bs.vh.2018.01.009|isbn=978-0-128-14359-9|pmid=29544627}}</ref> whereas the uterine cycle describes changes in the [[Endometrium|endometrial lining]] of the uterus.  Both cycles can be divided into phases.  The ovarian cycle consists of alternating [[follicular phase|follicular]] and [[luteal phase]]s, and the uterine cycle consists of [[menstruation]], the proliferative phase, and the secretory phase.{{sfn|Tortora|2017|p=944}} The menstrual cycle is controlled by the [[hypothalamus]] and the [[pituitary gland]] in the brain. The hypothalamus releases [[gonadotropin releasing hormone]] (GnRH), which causes the nearby anterior pituitary gland to release [[follicle-stimulating hormone]] (FSH) and [[luteinizing hormone]] (LH). Before [[puberty]] GnRH is released in steady quantities and at a steady rate. After puberty it is released in large pulses and the frequency and magnitude of these determine how much FSH and LH are produced by the pituitary.{{sfn|Tortora|2017|p=942}}
+The menstrual cycle encompasses the ovarian and uterine cycles. The ovarian cycle describes changes that occur in the [[Ovarian follicle|follicles]] of the [[ovary]],<ref name="pmid29544627">{{cite journal|vauthors=Richards JS|date=2018|title=The ovarian cycle|journal=Vitamins and Hormones|volume=107|issue=|pages=1–25|doi=10.1016/bs.vh.2018.01.009|isbn=978-0-128-14359-9|pmid=29544627 |type= Review}}</ref> whereas the uterine cycle describes changes in the [[Endometrium|endometrial lining]] of the uterus.  Both cycles can be divided into phases.  The ovarian cycle consists of alternating [[follicular phase|follicular]] and [[luteal phase]]s, and the uterine cycle consists of [[menstruation]], the proliferative phase, and the secretory phase.{{sfn|Tortora|2017|p=944}} The menstrual cycle is controlled by the [[hypothalamus]] and the [[pituitary gland]] in the brain. The hypothalamus releases [[gonadotropin releasing hormone]] (GnRH), which causes the nearby anterior pituitary gland to release [[follicle-stimulating hormone]] (FSH) and [[luteinizing hormone]] (LH). Before [[puberty]] GnRH is released in steady quantities and at a steady rate. After puberty it is released in large pulses and the frequency and magnitude of these determine how much FSH and LH are produced by the pituitary.{{sfn|Tortora|2017|p=942}}
-Measured from the first day of one menstruation to the first day of the next, the length of a menstrual cycle varies.<ref name="Reed2018" />  The cycle is often less regular at the beginning and end of a woman's reproductive life.<ref name="Reed2018" /> Beginning at puberty, a child's body begins to mature into an adult body capable of [[sexual reproduction]]; the first period (called [[menarche]]) occurs at around 12 years of age.<ref name="pmid29261991" /><ref name="pmid26703478" /> The cessation of menstrual cycles at the end of a woman's reproductive period at [[menopause]] commonly occurs between the ages of 45 and 55.<ref name="pmid27465713">{{cite journal |vauthors=Shadyab AH, Macera CA, Shaffer RA, Jain S, Gallo LC, Gass ML, Waring ME, Stefanick ML, LaCroix AZ |title=Ages at menarche and menopause and reproductive lifespan as predictors of exceptional longevity in women: the Women's Health Initiative |journal=Menopause (New York, N.Y.) |volume=24 |issue=1 |pages=35–44 |date=January 2017 |pmid=27465713 |pmc=5177476 |doi=10.1097/GME.0000000000000710 }}</ref>
+Measured from the first day of one menstruation to the first day of the next, the length of a menstrual cycle varies.<ref name="Reed2018" />  The cycle is often less regular at the beginning and end of a woman's reproductive life.<ref name="Reed2018" /> Beginning at puberty, a child's body begins to mature into an adult body capable of [[sexual reproduction]]; the first period (called [[menarche]]) occurs at around 12 years of age.<ref name="pmid29261991" /><ref name="pmid26703478" /> The cessation of menstrual cycles at the end of a woman's reproductive period at [[menopause]] commonly occurs between the ages of 45 and 55.<ref name="pmid27465713">{{cite journal |vauthors=Shadyab AH, Macera CA, Shaffer RA, Jain S, Gallo LC, Gass ML, Waring ME, Stefanick ML, LaCroix AZ |title=Ages at menarche and menopause and reproductive lifespan as predictors of exceptional longevity in women: the Women's Health Initiative |journal=Menopause (New York, N.Y.) |volume=24 |issue=1 |pages=35–44 |date=January 2017 |pmid=27465713 |pmc=5177476 |doi=10.1097/GME.0000000000000710 |type= Journal article}}</ref>
 === Ovarian cycle ===
-Between menarche and menopause the human ovaries regularly alternate between luteal and follicular phases during the monthly menstrual cycle.{{sfn | Sherwood | 2016 | p=741}} Stimulated by gradually increasing amounts of [[estrogen]] in the follicular phase, discharges of blood flow stop and the uterus lining thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one, or occasionally two, become dominant, while non-dominant follicles shrink and die. About mid-cycle, some 34–36 hours after the luteinizing hormone (LH) surges,<ref name= Reed2018>{{cite journal |vauthors= Reed BF, Carr BR, Feingold KR, et al |title= The Normal Menstrual Cycle and the Control of Ovulation  |journal= Endotext |date= 2018|pmid=25905282 |url= https://www.ncbi.nlm.nih.gov/books/NBK279054/?report=classic }}</ref> the dominant follicle releases an [[oocyte]], in an event called [[ovulation]].{{sfn | Sherwood | 2016 | p=747}}
+Between menarche and menopause the human ovaries regularly alternate between luteal and follicular phases during the monthly menstrual cycle.{{sfn | Sherwood | 2016 | p=741}} Stimulated by gradually increasing amounts of [[estrogen]] in the follicular phase, discharges of blood flow stop and the uterus lining thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one, or occasionally two, become dominant, while non-dominant follicles shrink and die. About mid-cycle, some 34–36 hours after the luteinizing hormone (LH) surges,<ref name= Reed2018>{{cite journal |vauthors= Reed BF, Carr BR, Feingold KR, et al |title= The Normal Menstrual Cycle and the Control of Ovulation  |journal= Endotext |date= 2018|pmid=25905282 |url= https://www.ncbi.nlm.nih.gov/books/NBK279054/?report=classic |type= Review}}</ref> the dominant follicle releases an [[oocyte]], in an event called [[ovulation]].{{sfn | Sherwood | 2016 | p=747}}
 After ovulation, the oocyte lives for 24 hours or less without [[Human fertilization|fertilization]],{{sfn|Tortora|2017|p=957}} while the remains of the dominant follicle in the ovary become a [[corpus luteum]]—a body with the primary function of producing large amounts of the hormone [[progesterone]].{{sfn|Tortora|2017|p=929}} Under the influence of progesterone, the uterine lining changes to prepare for potential [[Implantation (human embryo)|implantation]] of an [[embryo]] to establish a pregnancy. The thickness of the endometrium continues to increase in response to mounting levels of estrogen, which is released by the [[antral follicle]] (a mature ovarian follicle) into the blood circulation. Peak levels of estrogen are reached at around day thirteen of the cycle and coincide with ovulation. If implantation does not occur within about two weeks, the corpus luteum degenerates into the [[corpus albicans]], which does not produce hormones, causing a sharp drop in levels of both progesterone and estrogen. This hormone drop causes the uterus to loose its lining in menstruation; it is around this time that the lowest levels of estrogen are reached.{{sfn|Tortora|2017|pp=942–46}}
@@ Line 27: / Line 27: @@
 ==== Follicular phase ====
 {{main|Follicular phase}}
-The ovaries contain a finite number of [[Oogonium|egg stem cells]], [[granulosa cells]] and [[Theca of follicle|theca cells]], which together form primordial follicles.{{sfn|Tortora|2017|p=929}} Beginning at puberty, these mature to primary follicles independently of the  menstrual cycle.{{sfn | Watchman | 2020 | p=8}} The follicular phase is the first part of the ovarian cycle and it ends with the completion of the [[antral follicles]].{{sfn | Sherwood | 2016 | p=741}} [[Meiosis]] (cell  division) remains incomplete in the egg  cells until the antral follicle is formed. The development of the egg is called [[oogenesis]] and only one cell survives the [[Prophase#Meiotic_prophase|divisions]] to await fertilization. The other cells are discarded as [[polar body|polar bodies]], which cannot be fertilized.<ref name="pmid21268179">{{cite journal |vauthors=Schmerler S, Wessel GM |title=Polar bodies – more a lack of understanding than a lack of respect |journal=Molecular Reproduction and Development |volume=78 |issue=1 |pages=3–8 |date=January 2011 |pmid=21268179 |pmc=3164815 |doi=10.1002/mrd.21266 |url=}}</ref> The follicular phase shortens significantly with age, lasting around 14 days in women aged 18–24 compared with 10 days in women aged 40–44).{{sfn | Tortora | 2017 | pp=942–46}} During this phase usually only one ovarian follicle fully matures and gets ready to release an egg.{{sfn | Tortora | 2017 | p=945}}
+The ovaries contain a finite number of [[Oogonium|egg stem cells]], [[granulosa cells]] and [[Theca of follicle|theca cells]], which together form primordial follicles.{{sfn|Tortora|2017|p=929}} Beginning at puberty, these mature to primary follicles independently of the  menstrual cycle.{{sfn | Watchman | 2020 | p=8}} The follicular phase is the first part of the ovarian cycle and it ends with the completion of the [[antral follicles]].{{sfn | Sherwood | 2016 | p=741}} [[Meiosis]] (cell  division) remains incomplete in the egg  cells until the antral follicle is formed. The development of the egg is called [[oogenesis]] and only one cell survives the [[Prophase#Meiotic_prophase|divisions]] to await fertilization. The other cells are discarded as [[polar body|polar bodies]], which cannot be fertilized.<ref name="pmid21268179">{{cite journal |vauthors=Schmerler S, Wessel GM |title=Polar bodies – more a lack of understanding than a lack of respect |journal=Molecular Reproduction and Development |volume=78 |issue=1 |pages=3–8 |date=January 2011 |pmid=21268179 |pmc=3164815 |doi=10.1002/mrd.21266 |type= Review}}</ref> The follicular phase shortens significantly with age, lasting around 14 days in women aged 18–24 compared with 10 days in women aged 40–44).{{sfn | Tortora | 2017 | pp=942–46}} During this phase usually only one ovarian follicle fully matures and gets ready to release an egg.{{sfn | Tortora | 2017 | p=945}}
 Through the influence of a rise in [[follicle stimulating hormone]] (FSH) during the first days of the cycle, a few ovarian follicles are stimulated. These follicles, which have been developing for the better part of a year in a process known as [[folliculogenesis]], compete with each other for dominance. Under the influence of several hormones, all but one of these follicles will stop growing, while one dominant follicle in the ovary will continue to maturity. The remaining follicles die in a process called [[follicular atresia]].{{sfn|Johnson|2007|page=86}} [[Luteinising hormone]] (LH) stimulates further development of the ovarian follicle. The follicle that reaches maturity is called an antral follicle, and it contains the [[ovum]] (egg cell).{{sfn|Tortora|2017|p=942}}
@@ Line 41: / Line 41: @@
 Ovulation occurs when a mature egg is released from the ovarian follicles into the [[fallopian tube]] about 10 to 12 hours after the peak in LH levels.<ref name="Reed2018" /> Most times only one of the 15–20 follicles that have been stimulated reaches full maturity, and just one egg is released.{{sfn | Sadler | 2019 | p=48}} Ovulation only occurs in around 10% of cycles during the first two years following menarche, and by the age of 40–50 the number of ovarian follicles is depleted.{{sfn|Tortora|2017|p=953}} Luteinising hormone initiates ovulation at around day 14 and stimulates the formation of the corpus luteum. In turn, and following further stimulation by luteinising hormone, the corpus luteum produces and releases estrogen, progesterone, [[relaxin]] (which relaxes the uterus by inhibiting contractions of the [[myometrium]]), and [[inhibin]] (which inhibits secretion of more luteinising hormone).{{sfn|Tortora|2017|p=942}}
-The release of LH matures the egg and weakens the wall of the follicle in the ovary, causing the fully developed follicle to release its oocyte.{{sfn | Sherwood | 2016 | p=746}} If it is fertilized by a sperm, the  oocyte promptly matures into an [[ootid]]  which blocks the other [[spermatozoa|sperm cells]] and becomes a mature egg. If it is not fertilized by a sperm, the  oocyte will degenerate. The mature egg has a diameter of about {{cvt|0.1|mm}},<ref>{{Cite book|last1=Alberts|first1=Bruce|last2=Johnson|first2=Alexander|last3=Lewis|first3=Julian|last4=Raff|first4=Martin|last5=Roberts|first5=Keith|last6=Walter|first6=Peter|date=2002|chapter=Eggs |title=Molecular Biology of the Cell| edition=4th|isbn=0-8153-3218-1|chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK26842/|location=New York |publisher=Garland Science|name-list-style = vanc }}</ref> and is the largest human cell.<ref name="pmid30739329">{{cite journal |vauthors=Iussig B, Maggiulli R, Fabozzi G, Bertelle S, Vaiarelli A, Cimadomo D, Ubaldi FM, Rienzi L |title=A brief history of oocyte cryopreservation: Arguments and facts |journal=Acta Obstetricia et Gynecologica Scandinavica |volume=98 |issue=5 |pages=550–58 |date=May 2019 |pmid=30739329 |doi=10.1111/aogs.13569 |url=|doi-access=free }}</ref>
+The release of LH matures the egg and weakens the wall of the follicle in the ovary, causing the fully developed follicle to release its oocyte.{{sfn | Sherwood | 2016 | p=746}} If it is fertilized by a sperm, the  oocyte promptly matures into an [[ootid]]  which blocks the other [[spermatozoa|sperm cells]] and becomes a mature egg. If it is not fertilized by a sperm, the  oocyte will degenerate. The mature egg has a diameter of about {{cvt|0.1|mm}},<ref>{{Cite book|last1=Alberts|first1=Bruce|last2=Johnson|first2=Alexander|last3=Lewis|first3=Julian|last4=Raff|first4=Martin|last5=Roberts|first5=Keith|last6=Walter|first6=Peter|date=2002|chapter=Eggs |title=Molecular Biology of the Cell| edition=4th|isbn=0-8153-3218-1|chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK26842/|location=New York |publisher=Garland Science|name-list-style = vanc }}</ref> and is the largest human cell.<ref name="pmid30739329">{{cite journal |vauthors=Iussig B, Maggiulli R, Fabozzi G, Bertelle S, Vaiarelli A, Cimadomo D, Ubaldi FM, Rienzi L |title=A brief history of oocyte cryopreservation: Arguments and facts |journal=Acta Obstetricia et Gynecologica Scandinavica |volume=98 |issue=5 |pages=550–58 |date=May 2019 |pmid=30739329 |doi=10.1111/aogs.13569 |doi-access=free |type= Review}}</ref>
-Which of the two ovaries—left or right—ovulates appears random;{{sfn | Parker | 2019 | p=283}} no left and right coordinating process is known.<ref name=ov>{{cite journal | vauthors = Ecochard R, Gougeon A | title = Side of ovulation and cycle characteristics in normally fertile women | journal = Human Reproduction | volume = 15 | issue = 4 | pages = 752–55 | date = April 2000 | pmid = 10739814 | doi = 10.1093/humrep/15.4.752 | doi-access = free }}</ref> Occasionally both ovaries will release an egg;<ref name=ov/> if both eggs are fertilized, the result is [[fraternal twin]]s.<ref name=twins>{{cite web | title = Multiple Pregnancy: Twins or More&nbsp;— Topic Overview | work = WebMD Medical Reference from Healthwise | date = 16 January 2019| url = http://www.webmd.com/baby/tc/multiple-pregnancy-twins-or-more-topic-overview | access-date = 26 February 2021}}</ref> After release from the ovary, the egg is swept into the fallopian tube by the [[Fimbria (female reproductive system)|fimbria]]—a fringe of tissue at the end of each fallopian tube. After about a day, an unfertilized egg will disintegrate or dissolve in the fallopian tube, and a fertilized egg will reach the uterus in three to five days.{{sfn | Sadler | 2019 | p=36}}
+Which of the two ovaries—left or right—ovulates appears random;{{sfn | Parker | 2019 | p=283}} no left and right coordinating process is known.<ref name=ov>{{cite journal | vauthors = Ecochard R, Gougeon A | title = Side of ovulation and cycle characteristics in normally fertile women | journal = Human Reproduction | volume = 15 | issue = 4 | pages = 752–55 | date = April 2000 | pmid = 10739814 | doi = 10.1093/humrep/15.4.752 | doi-access = free |type= Journal article}}</ref> Occasionally both ovaries will release an egg;<ref name=ov/> if both eggs are fertilized, the result is [[fraternal twin]]s.<ref name=twins>{{cite web | title = Multiple Pregnancy: Twins or More&nbsp;— Topic Overview | work = WebMD Medical Reference from Healthwise | date = 16 January 2019| url = http://www.webmd.com/baby/tc/multiple-pregnancy-twins-or-more-topic-overview | access-date = 26 February 2021}}</ref> After release from the ovary, the egg is swept into the fallopian tube by the [[Fimbria (female reproductive system)|fimbria]]—a fringe of tissue at the end of each fallopian tube. After about a day, an unfertilized egg will disintegrate or dissolve in the fallopian tube, and a fertilized egg will reach the uterus in three to five days.{{sfn | Sadler | 2019 | p=36}}
-Fertilization usually takes place in the [[Ampulla of uterine tube|ampulla]], the widest section of the fallopian tubes. A fertilized egg immediately starts the process of [[Human embryogenesis|embryogenesis]] (development). The developing embryo takes about three days to reach the uterus, and another three days to implant into the endometrium. It has usually reached the [[blastocyst]] stage at the time of implantation: this is when pregnancy begins.{{sfn | Tortora | 2017 | p=959}} The loss of the corpus luteum is prevented by fertilization of the egg.  The [[syncytiotrophoblast]] (the outer layer of the resulting embryo-containing blastocyst that later becomes the outer layer of the placenta), produces [[human chorionic gonadotropin]] (hCG), which is very similar to LH and which preserves the corpus luteum. The corpus luteum continues to secrete progestoerone and estrogens at levels slightly above those at ovulation during the first few months of pregnancy. After this and for the rest of the pregnancy, the [[placenta]] secretes high levels of these hormones along with [[human chorionic gonadotropin]] (hCG), which stimulates the corpus luteum to secrete more progesterone and estrogens, blocking the menstrual cycle.{{sfn|Tortora|2017|page=976}} These hormones also prepare the mammary glands for milk{{efn|[[Breastfeeding]] women can experience complete suppression of follicular development, follicular development but no ovulation, or normal menstrual cycles can resume.<ref name="pmid25869631">{{cite journal |vauthors=Carr SL, Gaffield ME, Dragoman MV, Phillips S |title=Safety of the progesterone-releasing vaginal ring (PVR) among lactating women: A systematic review |journal=Contraception |volume=94 |issue=3 |pages=253–61 |date=September 2016 |pmid=25869631 |doi=10.1016/j.contraception.2015.04.001 |doi-access=free }}</ref>}} production.{{sfn|Tortora|2017|page=976}}
+Fertilization usually takes place in the [[Ampulla of uterine tube|ampulla]], the widest section of the fallopian tubes. A fertilized egg immediately starts the process of [[Human embryogenesis|embryogenesis]] (development). The developing embryo takes about three days to reach the uterus, and another three days to implant into the endometrium. It has usually reached the [[blastocyst]] stage at the time of implantation: this is when pregnancy begins.{{sfn | Tortora | 2017 | p=959}} The loss of the corpus luteum is prevented by fertilization of the egg.  The [[syncytiotrophoblast]] (the outer layer of the resulting embryo-containing blastocyst that later becomes the outer layer of the placenta), produces [[human chorionic gonadotropin]] (hCG), which is very similar to LH and which preserves the corpus luteum. The corpus luteum continues to secrete progestoerone and estrogens at levels slightly above those at ovulation during the first few months of pregnancy. After this and for the rest of the pregnancy, the [[placenta]] secretes high levels of these hormones along with [[human chorionic gonadotropin]] (hCG), which stimulates the corpus luteum to secrete more progesterone and estrogens, blocking the menstrual cycle.{{sfn|Tortora|2017|page=976}} These hormones also prepare the mammary glands for milk{{efn|[[Breastfeeding]] women can experience complete suppression of follicular development, follicular development but no ovulation, or normal menstrual cycles can resume.<ref name="pmid25869631">{{cite journal |vauthors=Carr SL, Gaffield ME, Dragoman MV, Phillips S |title=Safety of the progesterone-releasing vaginal ring (PVR) among lactating women: A systematic review |journal=Contraception |volume=94 |issue=3 |pages=253–61 |date=September 2016 |pmid=25869631 |doi=10.1016/j.contraception.2015.04.001 |doi-access=free |type= Review}}</ref>}} production.{{sfn|Tortora|2017|page=976}}
 ==== Luteal phase ====
@@ Line 53: / Line 53: @@
 === Uterine cycle ===
 [[File:Illu cervix.jpg|right|thumb|upright=1.6|The anatomy of the uterus]]
-The uterine cycle has three phases: menses, proliferative and secretory.<ref name="pmid30521482">{{cite journal |vauthors=Salamonsen LA |title=Women in Reproductive Science: Understanding human endometrial function |journal=Reproduction (Cambridge, England) |volume=158 |issue=6 |pages=F55–F67 |date=December 2019 |pmid=30521482 |doi=10.1530/REP-18-0518 |doi-access=free }}</ref>
+The uterine cycle has three phases: menses, proliferative and secretory.<ref name="pmid30521482">{{cite journal |vauthors=Salamonsen LA |title=Women in reproductive science: Understanding human endometrial function |journal=Reproduction (Cambridge, England) |volume=158 |issue=6 |pages=F55–F67 |date=December 2019 |pmid=30521482 |doi=10.1530/REP-18-0518 |doi-access=free |type= Review}}</ref>
 ====  Menstruation ====
 {{main|Menstruation}}
-Menstruation (also called menstrual bleeding, menses or a period) is the first and most evident phase of the uterine cycle and begins at puberty. Called menarche, the first period occurs at the age of around twelve or thirteen years.<ref name="pmid26703478">{{cite journal |vauthors=Papadimitriou A |title=The Evolution of the Age at Menarche from Prehistorical to Modern Times |journal=Journal of Pediatric and Adolescent Gynecology |volume=29 |issue=6 |pages=527–30 |date=December 2016 |pmid=26703478 |doi=10.1016/j.jpag.2015.12.002 |url=}}</ref> The average age is generally later in the [[developing world]] and earlier in [[developed world]].<ref name="pmid29778270">{{cite journal |vauthors=Alvergne A, Högqvist Tabor V |title=Is Female Health Cyclical? Evolutionary Perspectives on Menstruation |journal=Trends in Ecology & Evolution |volume=33 |issue=6 |pages=399–414 |date=June 2018 |pmid=29778270 |doi=10.1016/j.tree.2018.03.006 |arxiv=1704.08590 |s2cid=4581833 }}</ref>  In [[precocious puberty]], it can occur as early as age eight years,<ref name="pmid28591132">{{cite journal |vauthors=Ibitoye M, Choi C, Tai H, Lee G, Sommer M |title=Early menarche: A systematic review of its effect on sexual and reproductive health in low- and middle-income countries |journal=PLOS ONE |volume=12 |issue=6 |pages=e0178884 |date=2017 |pmid=28591132 |pmc=5462398 |doi=10.1371/journal.pone.0178884 |bibcode=2017PLoSO..1278884I }}</ref> and this can still be normal.<ref name=Women2014Men>{{cite web|title=Menstruation and the menstrual cycle fact sheet|url=http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.html|website=Office of Women's Health |publisher= US Department of Health and Human Services |access-date=25 June 2015|date=23 December 2014|url-status=dead|archive-url=https://web.archive.org/web/20150626134338/http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.html|archive-date=26 June 2015}}</ref><ref name="pmid29422239">{{cite journal |vauthors=Sultan C, Gaspari L, Maimoun L, Kalfa N, Paris F |title=Disorders of puberty |journal=Best Practice & Research. Clinical Obstetrics & Gynaecology |volume=48 |issue= |pages=62–89 |date=April 2018 |pmid=29422239 |doi=10.1016/j.bpobgyn.2017.11.004 |url=https://hal.umontpellier.fr/hal-01797379/file/2018%20Sultan%20et%20al.%2C%20Disorders%20of%20puberty.pdf}}</ref>
+Menstruation (also called menstrual bleeding, menses or a period) is the first and most evident phase of the uterine cycle and begins at puberty. Called menarche, the first period occurs at the age of around twelve or thirteen years.<ref name="pmid26703478">{{cite journal |vauthors=Papadimitriou A |title=The evolution of the age at menarche from prehistorical to modern times |journal=Journal of Pediatric and Adolescent Gynecology |volume=29 |issue=6 |pages=527–30 |date=December 2016 |pmid=26703478 |doi=10.1016/j.jpag.2015.12.002 |type= Review}}</ref> The average age is generally later in the [[developing world]] and earlier in [[developed world]].<ref name="pmid29778270">{{cite journal |vauthors=Alvergne A, Högqvist Tabor V |title=Is female health cyclical? Evolutionary perspectives on menstruation |journal=Trends in Ecology & Evolution |volume=33 |issue=6 |pages=399–414 |date=June 2018 |pmid=29778270 |doi=10.1016/j.tree.2018.03.006 |arxiv=1704.08590 |s2cid=4581833 |type= Review}}</ref>  In [[precocious puberty]], it can occur as early as age eight years,<ref name="pmid28591132">{{cite journal |vauthors=Ibitoye M, Choi C, Tai H, Lee G, Sommer M |title=Early menarche: A systematic review of its effect on sexual and reproductive health in low- and middle-income countries |journal=PLOS ONE |volume=12 |issue=6 |pages=e0178884 |date=2017 |pmid=28591132 |pmc=5462398 |doi=10.1371/journal.pone.0178884 |bibcode=2017PLoSO..1278884I |type= Review}}</ref> and this can still be normal.<ref name=Women2014Men>{{cite web|title=Menstruation and the menstrual cycle fact sheet|url=http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.html|website=Office of Women's Health |publisher= US Department of Health and Human Services |access-date=25 June 2015|date=23 December 2014|url-status=dead|archive-url=https://web.archive.org/web/20150626134338/http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.html|archive-date=26 June 2015}}</ref><ref name="pmid29422239">{{cite journal |vauthors=Sultan C, Gaspari L, Maimoun L, Kalfa N, Paris F |title=Disorders of puberty |journal=Best Practice & Research. Clinical Obstetrics & Gynaecology |volume=48 |issue= |pages=62–89 |date=April 2018 |pmid=29422239 |doi=10.1016/j.bpobgyn.2017.11.004 |url=https://hal.umontpellier.fr/hal-01797379/file/2018%20Sultan%20et%20al.%2C%20Disorders%20of%20puberty.pdf|type= Review}}</ref>
 Menstruation is initiated each month by falling levels of estrogen and progesterone and the release of [[prostaglandin]]s,{{sfn|Tortora|2017|p=945}} which constrict the [[spiral artery|spiral arteries]]. This causes them to [[spasm]], contract and break up.{{sfn|Johnson|2007|pages=152}} The blood supply to the endometrium is cut off and the cells of the top layer of the endometrium (the stratum functionalis) become deprived of oxygen and die. Later the whole layer is lost and only the bottom layer, the stratum basalis, is left in place.{{sfn|Tortora|2017|page=945}} An [[enzyme]] called [[plasmin]] breaks up the [[blood clotting|blood clots]] in the menstrual fluid, which eases the flow of blood and broken down lining from the uterus.{{sfn | Tortora | 2017 | p=600}}
-The flow of blood normally serves as a sign that a woman has not become pregnant, but this cannot be taken as certainty, as several factors can cause [[Vaginal bleeding#Pregnant women|bleeding during pregnancy]].<ref name="pmid27166462">{{cite journal |vauthors=Breeze C |title=Early pregnancy bleeding |journal=Australian Family Physician |volume=45 |issue=5 |pages=283–86 |date=May 2016 |pmid=27166462 }}</ref> Menstruation occurs on average once a month from menarche to menopause, which corresponds with a woman's fertile years. The average age of menopause in women is 52 years, and it typically occurs between 45 and 55 years of age.<ref name="pmid27022074">{{cite journal |vauthors=Towner MC, Nenko I, Walton SE |title=Why do women stop reproducing before menopause? A life-history approach to age at last birth |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=371 |issue=1692 |pages=20150147 |date=April 2016 |pmid=27022074 |pmc=4822427 |doi=10.1098/rstb.2015.0147 }}</ref>
+The flow of blood normally serves as a sign that a woman has not become pregnant, but this cannot be taken as certainty, as several factors can cause [[Vaginal bleeding#Pregnant women|bleeding during pregnancy]].<ref name="pmid27166462">{{cite journal |vauthors=Breeze C |title=Early pregnancy bleeding |journal=Australian Family Physician |volume=45 |issue=5 |pages=283–86 |date=May 2016 |pmid=27166462 |type= Review}}</ref> Menstruation occurs on average once a month from menarche to menopause, which corresponds with a woman's fertile years. The average age of menopause in women is 52 years, and it typically occurs between 45 and 55 years of age.<ref name="pmid27022074">{{cite journal |vauthors=Towner MC, Nenko I, Walton SE |title=Why do women stop reproducing before menopause? A life-history approach to age at last birth |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=371 |issue=1692 |pages=20150147 |date=April 2016 |pmid=27022074 |pmc=4822427 |doi=10.1098/rstb.2015.0147 |type= Review}}</ref>
-''Eumenorrhea'' denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal).<ref name=allmenses>{{cite web | first=John M | last=Goldenring | name-list-style = vanc | title=All About Menstruation |url=http://www.webmd.com/a-to-z-guides/all-about-menstruation | date=1 February 2019 | website=WebMD | access-date=26 February 2021}}</ref> The average [[Bleeding|blood loss]] during menstruation is 30 milliliters (mL),  and more than 80 mL is considered abnormal.<ref name="Reed2018" /> Women who experience [[menorrhagia]] (heavy menstrual bleeding) are more susceptible to [[iron deficiency (medicine)|iron deficiency]] than the average person.<ref name=iron>{{cite journal | vauthors = Harvey LJ, Armah CN, Dainty JR, Foxall RJ, John Lewis D, Langford NJ, Fairweather-Tait SJ | title = Impact of menstrual blood loss and diet on iron deficiency among women in the UK | journal = The British Journal of Nutrition | volume = 94 | issue = 4 | pages = 557–64 | date = October 2005 | pmid = 16197581 | doi = 10.1079/BJN20051493 | doi-access = free }}</ref>
+''Eumenorrhea'' denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal).<ref name=allmenses>{{cite web | first=John M | last=Goldenring | name-list-style = vanc | title=All About Menstruation |url=http://www.webmd.com/a-to-z-guides/all-about-menstruation | date=1 February 2019 | website=WebMD | access-date=26 February 2021}}</ref> The average [[Bleeding|blood loss]] during menstruation is 30 milliliters (mL),  and more than 80 mL is considered abnormal.<ref name="Reed2018" /> Women who experience [[menorrhagia]] (heavy menstrual bleeding) are more susceptible to [[iron deficiency (medicine)|iron deficiency]] than the average person.<ref name=iron>{{cite journal | vauthors = Harvey LJ, Armah CN, Dainty JR, Foxall RJ, John Lewis D, Langford NJ, Fairweather-Tait SJ | title = Impact of menstrual blood loss and diet on iron deficiency among women in the UK | journal = The British Journal of Nutrition | volume = 94 | issue = 4 | pages = 557–64 | date = October 2005 | pmid = 16197581 | doi = 10.1079/BJN20051493 | doi-access = free| type= Comparative study}}</ref>
 ==== Proliferative phase ====
 The proliferative phase is the second phase of the uterine cycle when estrogen causes the lining of the uterus to grow and proliferate.{{sfn | Ugwumadu | 2014 | p= 117}} The latter part of the follicular phase overlaps with the proliferative phase of the uterine cycle.{{sfn|Parker|2019|p=283}} As they mature, the ovarian follicles secrete increasing amounts of estradiol, an estrogen. The estrogens initiate the formation of a new layer of endometrium in the uterus with the spiral arterioles.{{sfn|Tortora|2017|p=944}}
-As estrogen levels increase, cells in the cervix produce a type of [[cervical mucus]]<ref>{{cite journal |vauthors=Simmons RG, Jennings V |title=Fertility awareness-based methods of family planning |journal=Best Practice & Research. Clinical Obstetrics & Gynaecology |volume=66 |pages=68–82 |date=July 2020 |pmid=32169418 |doi=10.1016/j.bpobgyn.2019.12.003 |doi-access=free }}</ref> that has a higher [[pH]] and is less [[viscosity|viscous]] than usual, rendering it more friendly to sperm.{{sfn|Tortora|2017|pp=936–37}} This increases the chances of fertilization, which occurs around day 11 to day 14.{{sfn|Tortora|2017|p=957}} This cervical mucus can be detected as a vaginal discharge that is copious and resembles raw egg whites.<ref name= Su2017 /> For women who are practicing [[fertility awareness]], it is a sign that ovulation is about to take place.<ref name= Su2017>{{cite journal |vauthors=Su HW, Yi YC, Wei TY, Chang TC, Cheng CM |title=Detection of ovulation, a review of currently available methods |journal=Bioeng Transl Med |volume=2 |issue=3 |pages=238–246 |date=September 2017 |pmid=29313033 |pmc=5689497 |doi=10.1002/btm2.10058 }}</ref>
+As estrogen levels increase, cells in the cervix produce a type of [[cervical mucus]]<ref>{{cite journal |vauthors=Simmons RG, Jennings V |title=Fertility awareness-based methods of family planning |journal=Best Practice & Research. Clinical Obstetrics & Gynaecology |volume=66 |pages=68–82 |date=July 2020 |pmid=32169418 |doi=10.1016/j.bpobgyn.2019.12.003 |doi-access=free |type= Review}}</ref> that has a higher [[pH]] and is less [[viscosity|viscous]] than usual, rendering it more friendly to sperm.{{sfn|Tortora|2017|pp=936–37}} This increases the chances of fertilization, which occurs around day 11 to day 14.{{sfn|Tortora|2017|p=957}} This cervical mucus can be detected as a vaginal discharge that is copious and resembles raw egg whites.<ref name= Su2017 /> For women who are practicing [[fertility awareness]], it is a sign that ovulation is about to take place.<ref name= Su2017>{{cite journal |vauthors=Su HW, Yi YC, Wei TY, Chang TC, Cheng CM |title=Detection of ovulation, a review of currently available methods |journal=Bioeng Transl Med |volume=2 |issue=3 |pages=238–246 |date=September 2017 |pmid=29313033 |pmc=5689497 |doi=10.1002/btm2.10058 |type= Review}}</ref>
 ==== Secretory phase ====
-The secretory phase is the final phase of the uterine cycle and it corresponds to the luteal phase of the ovarian cycle. During the secretory phase, the corpus luteum produces progesterone, which plays a vital role in making the endometrium receptive to the implantation of a [[blastocyst]] (a fertilized egg, which has begun to grow).<ref name="pmid30929718">{{cite journal |vauthors=Lessey BA, Young SL |title=What exactly is endometrial receptivity? |journal=Fertility and Sterility |volume=111 |issue=4 |pages=611–17|date=April 2019 |pmid=30929718 |doi=10.1016/j.fertnstert.2019.02.009 |url=}}</ref> [[Glycogen]], [[lipid]]s,  and [[protein]]s are secreted into the uterus<ref name="pmid26661899">{{cite journal |vauthors=Salamonsen LA, Evans J, Nguyen HP, Edgell TA |title=The Microenvironment of Human Implantation: Determinant of Reproductive Success |journal=American Journal of Reproductive Immunology (New York, N.Y. : 1989) |volume=75 |issue=3 |pages=218–25 |date=March 2016 |pmid=26661899 |doi=10.1111/aji.12450 |url=}}</ref> and the cervical mucus thickens.<ref name="pmid28801053">{{cite journal |vauthors=Han L, Taub R, Jensen JT |title=Cervical mucus and contraception: what we know and what we don't |journal=Contraception |volume=96 |issue=5 |pages=310–321 |date=November 2017 |pmid=28801053 |doi=10.1016/j.contraception.2017.07.168 |url=}}</ref> In early pregnancy progesterone also increases  blood flow and reduces the [[Muscle contraction|contractility]] of the [[smooth muscle]] in the uterus{{sfn|Tortora|2017|p= 942}} and raises the woman's [[basal body temperature]].<ref name="pmid28488202">{{cite journal |vauthors=Charkoudian N, Hart EC, Barnes JN, Joyner MJ |title=Autonomic control of body temperature and blood pressure: influences of female sex hormones |journal=Clinical Autonomic Research |volume=27 |issue=3 |pages=149–55 |date=June 2017 |pmid=28488202 |doi=10.1007/s10286-017-0420-z |s2cid=3773043 |url=https://research-information.bris.ac.uk/ws/files/152610705/Charkoudian_CAR_review_final.pdf}}</ref>
+The secretory phase is the final phase of the uterine cycle and it corresponds to the luteal phase of the ovarian cycle. During the secretory phase, the corpus luteum produces progesterone, which plays a vital role in making the endometrium receptive to the implantation of a [[blastocyst]] (a fertilized egg, which has begun to grow).<ref name="pmid30929718">{{cite journal |vauthors=Lessey BA, Young SL |title=What exactly is endometrial receptivity? |journal=Fertility and Sterility |volume=111 |issue=4 |pages=611–17|date=April 2019 |pmid=30929718 |doi=10.1016/j.fertnstert.2019.02.009 |type= Review}}</ref> [[Glycogen]], [[lipid]]s,  and [[protein]]s are secreted into the uterus<ref name="pmid26661899">{{cite journal |vauthors=Salamonsen LA, Evans J, Nguyen HP, Edgell TA |title=The microenvironment of human implantation: determinant of reproductive success |journal=American Journal of Reproductive Immunology (New York, N.Y. : 1989) |volume=75 |issue=3 |pages=218–25 |date=March 2016 |pmid=26661899 |doi=10.1111/aji.12450 |type= Review}}</ref> and the cervical mucus thickens.<ref name="pmid28801053">{{cite journal |vauthors=Han L, Taub R, Jensen JT |title=Cervical mucus and contraception: what we know and what we don't |journal=Contraception |volume=96 |issue=5 |pages=310–321 |date=November 2017 |pmid=28801053 |doi=10.1016/j.contraception.2017.07.168 |type= Review}}</ref> In early pregnancy progesterone also increases  blood flow and reduces the [[Muscle contraction|contractility]] of the [[smooth muscle]] in the uterus{{sfn|Tortora|2017|p= 942}} and raises the woman's [[basal body temperature]].<ref name="pmid28488202">{{cite journal |vauthors=Charkoudian N, Hart EC, Barnes JN, Joyner MJ |title=Autonomic control of body temperature and blood pressure: influences of female sex hormones |journal=Clinical Autonomic Research |volume=27 |issue=3 |pages=149–55 |date=June 2017 |pmid=28488202 |doi=10.1007/s10286-017-0420-z |s2cid=3773043 |url=https://research-information.bris.ac.uk/ws/files/152610705/Charkoudian_CAR_review_final.pdf |type= Review}}</ref>
 If pregnancy does not occur the falling levels of estrogen trigger menstruation and the ovarian and uterine cycles start over again.{{sfn|Tortora|2017|page=600}}
@@ Line 78: / Line 78: @@
 == Menstrual health ==
 [[File:Human ovarian follicle.jpg|thumb|A human primary ovarian follicle viewed by [[microscopy]]. The round oocyte stained red in the center is surrounded by  a layer of granulosa cells, which are enveloped by the basement membrane and theca cells. The magnification is around 1000 times. ([[H&E stain]])]]
-Some women experience problems sufficient to disrupt their lives as a result their menstrual cycle.<ref name="pmid32809533">{{cite book |vauthors=Gudipally PR, Sharma GK |title=Premenstrual Syndrome |publisher=StatPearls [Internet]|date=2020 |pmid=32809533 }}</ref> These include [[acne vulgaris|acne]], tender breasts, bloating, feeling tired, irritability mood changes,<ref name=Women2014PMS/> and [[premenstrual syndrome]] (PMS). More severe problems such as [[premenstrual dysphoric disorder]] are experienced by 3 to 8% of women.<ref name="Reed2018" /><ref name="pmid29298169">{{cite journal |vauthors=Appleton SM |title=Premenstrual Syndrome: Evidence-based Evaluation and Treatment |journal=Clinical Obstetrics and Gynecology |volume=61 |issue=1 |pages=52–61 |date=March 2018 |pmid=29298169 |doi=10.1097/GRF.0000000000000339 |s2cid=28184066 |url=}}</ref>  [[Dysmenorrhea]] is frequently a source of pelvic pain,<ref name=Dysmenorrheastat>{{cite journal | vauthors = Nagy H, Khan MA | title = Dysmenorrhea | journal = StatPearls | date = 2020 | pmid = 32809669 }}</ref> causing [[cramps]] in the abdomen, back, or upper thighs that occur during the first few days of menstruation.<ref name="pmid30098748">{{cite journal |vauthors=Baker FC, Lee KA |title=Menstrual Cycle Effects on Sleep |journal=Sleep Medicine Clinics |volume=13 |issue=3 |pages=283–94 |date=September 2018 |pmid=30098748 |doi=10.1016/j.jsmc.2018.04.002 }}</ref>
+Some women experience problems sufficient to disrupt their lives as a result their menstrual cycle.<ref name="pmid32809533">{{cite book |vauthors=Gudipally PR, Sharma GK |title=Premenstrual syndrome |publisher=StatPearls [Internet]|date=2020 |pmid=32809533 |type= Review}}</ref> These include [[acne vulgaris|acne]], tender breasts, bloating, feeling tired, irritability mood changes,<ref name=Women2014PMS/> and [[premenstrual syndrome]] (PMS). More severe problems such as [[premenstrual dysphoric disorder]] are experienced by 3 to 8% of women.<ref name="Reed2018" /><ref name="pmid29298169">{{cite journal |vauthors=Appleton SM |title=Premenstrual syndrome: evidence-based evaluation and treatment |journal=Clinical Obstetrics and Gynecology |volume=61 |issue=1 |pages=52–61 |date=March 2018 |pmid=29298169 |doi=10.1097/GRF.0000000000000339 |s2cid=28184066 |type= Review}}</ref>  [[Dysmenorrhea]] is frequently a source of pelvic pain,<ref name=Dysmenorrheastat>{{cite journal | vauthors = Nagy H, Khan MA | title = Dysmenorrhea | journal = StatPearls | date = 2020 | pmid = 32809669 |type= Review}}</ref> causing [[cramps]] in the abdomen, back, or upper thighs that occur during the first few days of menstruation.<ref name="pmid30098748">{{cite journal |vauthors=Baker FC, Lee KA |title=Menstrual cycle effects on sleep |journal=Sleep Medicine Clinics |volume=13 |issue=3 |pages=283–94 |date=September 2018 |pmid=30098748 |doi=10.1016/j.jsmc.2018.04.002 |type= Review}}</ref>
-These issues can significantly affect a woman's health and quality of life and timely interventions can improve the lives of these women.<ref name="pmid31378287">{{cite journal |vauthors=Matteson KA, Zaluski KM |title=Menstrual Health as a Part of Preventive Health Care |journal=Obstetrics and Gynecology Clinics of North America |volume=46 |issue=3 |pages=441–53 |date=September 2019 |pmid=31378287 |doi=10.1016/j.ogc.2019.04.004 }}</ref>
+These issues can significantly affect a woman's health and quality of life and timely interventions can improve the lives of these women.<ref name="pmid31378287">{{cite journal |vauthors=Matteson KA, Zaluski KM |title=Menstrual health as a part of preventive health care |journal=Obstetrics and Gynecology Clinics of North America |volume=46 |issue=3 |pages=441–53 |date=September 2019 |pmid=31378287 |doi=10.1016/j.ogc.2019.04.004 |type= Review}}</ref>
-When menstruation begins, symptoms of PMS such as [[mastalgia|breast tenderness]] and irritability generally decrease.<ref name=allmenses/>  In some women, ovulation features a characteristic pain{{efn|Uncharacteristic mid-cycle pain may be caused by medical conditions such as [[ectopic pregnancy]] or ruptured [[ovarian cyst]]<ref>{{cite journal |vauthors=Kruszka PS, Kruszka SJ |title=Evaluation of acute pelvic pain in women |journal=Am Fam Physician |volume=82 |issue=2 |pages=141–47 |date=July 2010 |pmid=20642266 |url= https://www.aafp.org/afp/2010/0715/p141.html}}</ref><ref>{{cite book|title= Acute and Emergency Care in Athletic Training |vauthors= Cleary M, Flanagan KW |publisher= Human Kinetics |date= 2019 |page= [https://books.google.com/books?id=_dWLDwAAQBAJ&pg=PA340&dq=Mittelschmerz+ectopic&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiEufDo15LvAhXaaM0KHdTHBbYQuwUwAHoECAAQCA#v=onepage&q=Mittelschmerz%20ectopic&f=false 340]}}</ref> or may be confused with [[appendicitis]].<ref>{{cite journal |vauthors=Brott NR, Le JK |title= Mittelschmerz |journal= Stat Pearls [Internet] |date= 2020|pmid=31747229 |url= https://www.ncbi.nlm.nih.gov/books/NBK549822/}}</ref>}} called ''[[mittelschmerz]]'' (a German term meaning ''middle pain'').<ref name=allmenses/> This occurs when an egg does not enter the fallopian tube but the [[pelvic cavity]] where it breaks up. The cause of the pain is the small amount of blood loss associated with the ruptured follicle.{{sfn|Tortora|2017|p=945}}
+When menstruation begins, symptoms of PMS such as [[mastalgia|breast tenderness]] and irritability generally decrease.<ref name=allmenses/>  In some women, ovulation features a characteristic pain{{efn|Uncharacteristic mid-cycle pain may be caused by medical conditions such as [[ectopic pregnancy]] or ruptured [[ovarian cyst]]<ref>{{cite journal |vauthors=Kruszka PS, Kruszka SJ |title=Evaluation of acute pelvic pain in women |journal=Am Fam Physician |volume=82 |issue=2 |pages=141–47 |date=July 2010 |pmid=20642266 |url= https://www.aafp.org/afp/2010/0715/p141.html|type= Review}}</ref><ref>{{cite book|title= Acute and Emergency Care in Athletic Training |vauthors= Cleary M, Flanagan KW |publisher= Human Kinetics |date= 2019 |page= [https://books.google.com/books?id=_dWLDwAAQBAJ&pg=PA340&dq=Mittelschmerz+ectopic&hl=en&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwiEufDo15LvAhXaaM0KHdTHBbYQuwUwAHoECAAQCA#v=onepage&q=Mittelschmerz%20ectopic&f=false 340]}}</ref> or may be confused with [[appendicitis]].<ref>{{cite journal |vauthors=Brott NR, Le JK |title= Mittelschmerz |journal= Stat Pearls [Internet] |date= 2020|pmid=31747229 |url= https://www.ncbi.nlm.nih.gov/books/NBK549822/ |type= Review}}</ref>}} called ''[[mittelschmerz]]'' (a German term meaning ''middle pain'').<ref name=allmenses/> This occurs when an egg does not enter the fallopian tube but the [[pelvic cavity]] where it breaks up. The cause of the pain is the small amount of blood loss associated with the ruptured follicle.{{sfn|Tortora|2017|p=945}}
-Even when normal, the changes in hormone levels during the menstrual cycle can increase the incidence of disorders such as [[autoimmune disease]]s,<ref name="pmid28390570">{{cite journal |vauthors=Talsania M, Scofield RH |title=Menopause and Rheumatic Disease |journal=Rheumatic Diseases Clinics of North America |volume=43 |issue=2 |pages=287–302 |date=May 2017 |pmid=28390570 |pmc=5385852 |doi=10.1016/j.rdc.2016.12.011 |url=}}</ref> which might be caused by estrogen enhancement of the [[immune system]].<ref name="Reed2018" />
+Even when normal, the changes in hormone levels during the menstrual cycle can increase the incidence of disorders such as [[autoimmune disease]]s,<ref name="pmid28390570">{{cite journal |vauthors=Talsania M, Scofield RH |title=Menopause and rheumatic disease |journal=Rheumatic Diseases Clinics of North America |volume=43 |issue=2 |pages=287–302 |date=May 2017 |pmid=28390570 |pmc=5385852 |doi=10.1016/j.rdc.2016.12.011 |type= Review}}</ref> which might be caused by estrogen enhancement of the [[immune system]].<ref name="Reed2018" />
 === Hormonal contraception ===
@@ Line 90: / Line 90: @@
 ==Evolution and other species==
 {{further|Menstruation (mammal)}}
-Most [[female mammals]] have an [[estrous cycle]], but only ten primate species, four [[bat]] species, the [[elephant shrew]] and the [[spiny mouse]] have a [[Menstruation (mammal)|menstrual cycle]].<ref>{{cite journal | vauthors = Bellofiore N, Ellery SJ, Mamrot J, Walker DW, Temple-Smith P, Dickinson H | title = First evidence of a menstruating rodent: the spiny mouse&nbsp;(Acomys&nbsp;cahirinus) | journal = American Journal of Obstetrics and Gynecology | volume = 216 | issue = 1 | pages = 40.e1–40.e11 | date = January 2017 | pmid = 27503621 | doi = 10.1016/j.ajog.2016.07.041 | s2cid = 88779 }}</ref> The cycles are the same as in humans apart from the length, which ranges from 21 to 37 days.<ref name="pmid32129461"/> The lack of immediate relationship between these groups suggests that four distinct evolutionary events have caused menstruation to arise.<ref name=Emera2012/> In species that have a menstrual cycle, ovulation is not obvious to potential mates and there is no [[mating season]].<ref name="pmid31999507">{{cite journal |vauthors=Schjenken JE, Robertson SA |title=The Female Response to Seminal Fluid |journal=Physiological Reviews |volume=100 |issue=3 |pages=1077–117 |date=July 2020 |pmid=31999507 |doi=10.1152/physrev.00013.2018 }}</ref><ref name="pmid27616559">{{cite journal |vauthors=Muller MN |title=Testosterone and reproductive effort in male primates |journal=Hormones and Behavior |volume=91 |pages=36–51 |date=May 2017 |pmid=27616559 |pmc=5342957 |doi=10.1016/j.yhbeh.2016.09.001 }}</ref>  There are four theories on the evolutionary significance of menstruation:<ref name=Emera2012>{{cite journal |vauthors=Emera D, Romero R, Wagner G |title=The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness |journal=BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology |volume=34 |issue=1 |pages=26–35 |date=January 2012 |pmid=22057551 |pmc=3528014 |doi=10.1002/bies.201100099 |lay-url= http://www.bbc.com/earth/story/20150420-why-do-women-have-periods |lay-source= BBC Earth |lay-date= April 20, 2015}}</ref>
+Most [[female mammals]] have an [[estrous cycle]], but only ten primate species, four [[bat]] species, the [[elephant shrew]] and the [[spiny mouse]] have a [[Menstruation (mammal)|menstrual cycle]].<ref>{{cite journal | vauthors = Bellofiore N, Ellery SJ, Mamrot J, Walker DW, Temple-Smith P, Dickinson H | title = First evidence of a menstruating rodent: the spiny mouse&nbsp;(Acomys&nbsp;cahirinus) | journal = American Journal of Obstetrics and Gynecology | volume = 216 | issue = 1 | pages = 40.e1–40.e11 | date = January 2017 | pmid = 27503621 | doi = 10.1016/j.ajog.2016.07.041 | s2cid = 88779 |type= Journal article}}</ref> The cycles are the same as in humans apart from the length, which ranges from 21 to 37 days.<ref name="pmid32129461"/> The lack of immediate relationship between these groups suggests that four distinct evolutionary events have caused menstruation to arise.<ref name=Emera2012/> In species that have a menstrual cycle, ovulation is not obvious to potential mates and there is no [[mating season]].<ref name="pmid31999507">{{cite journal |vauthors=Schjenken JE, Robertson SA |title=The female response to seminal fluid |journal=Physiological Reviews |volume=100 |issue=3 |pages=1077–117 |date=July 2020 |pmid=31999507 |doi=10.1152/physrev.00013.2018 |type= Review}}</ref><ref name="pmid27616559">{{cite journal |vauthors=Muller MN |title=Testosterone and reproductive effort in male primates |journal=Hormones and Behavior |volume=91 |pages=36–51 |date=May 2017 |pmid=27616559 |pmc=5342957 |doi=10.1016/j.yhbeh.2016.09.001 |type= Review}}</ref>  There are four theories on the evolutionary significance of menstruation:<ref name=Emera2012>{{cite journal |vauthors=Emera D, Romero R, Wagner G |title=The evolution of menstruation: a new model for genetic assimilation: explaining molecular origins of maternal responses to fetal invasiveness |journal=BioEssays : News and Reviews in Molecular, Cellular and Developmental Biology |volume=34 |issue=1 |pages=26–35 |date=January 2012 |pmid=22057551 |pmc=3528014 |doi=10.1002/bies.201100099 |type= Journal article |lay-url= http://www.bbc.com/earth/story/20150420-why-do-women-have-periods |lay-source= BBC Earth |lay-date= April 20, 2015}}</ref>
-# Control of sperm-borne pathogens.<ref name="pmid18046752">{{cite journal |vauthors=Martin RD |title=The evolution of human reproduction: a primatological perspective |journal=American Journal of Physical Anthropology |volume=Suppl 45 |issue= |pages=59–84 |date=2007 |pmid=18046752 |doi=10.1002/ajpa.20734 }}</ref><ref name="pmid9618925">{{cite journal |vauthors=Finn CA |title=Menstruation: a nonadaptive consequence of uterine evolution |journal=The Quarterly Review of Biology |volume=73 |issue=2 |pages=163–73 |date=June 1998|pmid=9618925|doi=10.1086/420183 |s2cid=25135630 }}</ref><ref name="pmid8210311">{{cite journal |vauthors=Profet M |title=Menstruation as a defense against pathogens transported by sperm |journal=The Quarterly Review of Biology |volume=68 |issue=3 |pages=335–86 |date=September 1993 |pmid=8210311 |doi=10.1086/418170 |s2cid=23738569 }}</ref>  This hypothesis held that menstruation protected the uterus against [[pathogen]]s introduced by [[sperm]]. Hypothesis 1 does not take into account that [[Sexual intercourse|copulation]] can take place weeks before menstruation and that potentially infectious [[semen]] is not controlled by menstruation in other species.<ref name=Emera2012/>
+# Control of sperm-borne pathogens.<ref name="pmid18046752">{{cite journal |vauthors=Martin RD |title=The evolution of human reproduction: a primatological perspective |journal=American Journal of Physical Anthropology |volume=Suppl 45 |issue= |pages=59–84 |date=2007 |pmid=18046752 |doi=10.1002/ajpa.20734 |type= Review}}</ref><ref name="pmid9618925">{{cite journal |vauthors=Finn CA |title=Menstruation: a nonadaptive consequence of uterine evolution |journal=The Quarterly Review of Biology |volume=73 |issue=2 |pages=163–73 |date=June 1998|pmid=9618925|doi=10.1086/420183 |s2cid=25135630 |type= Review}}</ref><ref name="pmid8210311">{{cite journal |vauthors=Profet M |title=Menstruation as a defense against pathogens transported by sperm |journal=The Quarterly Review of Biology |volume=68 |issue=3 |pages=335–86 |date=September 1993 |pmid=8210311 |doi=10.1086/418170 |s2cid=23738569 |type= Review}}</ref>  This hypothesis held that menstruation protected the uterus against [[pathogen]]s introduced by [[sperm]]. Hypothesis 1 does not take into account that [[Sexual intercourse|copulation]] can take place weeks before menstruation and that potentially infectious [[semen]] is not controlled by menstruation in other species.<ref name=Emera2012/>
-# Energy conservation.<ref name="pmid9618925"/><ref name="pmid8693059">{{cite journal |vauthors=Strassmann BI |title=The evolution of endometrial cycles and menstruation |journal=The Quarterly Review of Biology |volume=71 |issue=2 |pages=181–220 |date=June 1996 |pmid=8693059 |doi=10.1086/419369 |s2cid=6207295 }}</ref> This hypothesis claimed that it took less energy to rebuild a uterine lining than to maintain it if pregnancy did not occur.  Hypothesis&nbsp;2 does not explain other species that also do not maintain a uterine lining but do not menstruate.<ref name= Emera2012/>
+# Energy conservation.<ref name="pmid9618925"/><ref name="pmid8693059">{{cite journal |vauthors=Strassmann BI |title=The evolution of endometrial cycles and menstruation |journal=The Quarterly Review of Biology |volume=71 |issue=2 |pages=181–220 |date=June 1996 |pmid=8693059 |doi=10.1086/419369 |s2cid=6207295 |type= Review}}</ref> This hypothesis claimed that it took less energy to rebuild a uterine lining than to maintain it if pregnancy did not occur.  Hypothesis&nbsp;2 does not explain other species that also do not maintain a uterine lining but do not menstruate.<ref name= Emera2012/>
-# A theory based on spontaneous [[decidualization]] (a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy, in which the endometrium changes into the [[decidua]]).  Decidualization leads to the development of the [[endothelium]], which involves cells of the immune system,<ref name="pmid32129461">{{cite journal |vauthors=Catalini L, Fedder J |title=Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom† |journal=Biology of Reproduction |volume=102 |issue=6 |pages=1160–1169 |date=May 2020 |pmid=32129461 |pmc=7253787 |doi=10.1093/biolre/ioaa029 |url=}}</ref> the formation of a new blood supply, hormones and tissue differentiation. In non-menstruating mammals, decidualization is driven by the embryo, not the mother.<ref name="pmid9618925"/> It evolved in some placental mammals because it confers advantages in that it allows females to prepare for pregnancy without needing a signal from the fetus.<ref name= Emera2012/> Hypothesis&nbsp;3 defers to an explanation of the evolutionary origin of spontaneous decidualization and does not explain the evolution of menstruation alone.<ref name= Emera2012/>
+# A theory based on spontaneous [[decidualization]] (a process that results in significant changes to cells of the endometrium in preparation for, and during, pregnancy, in which the endometrium changes into the [[decidua]]).  Decidualization leads to the development of the [[endothelium]], which involves cells of the immune system,<ref name="pmid32129461">{{cite journal |vauthors=Catalini L, Fedder J |title=Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom† |journal=Biology of Reproduction |volume=102 |issue=6 |pages=1160–1169 |date=May 2020 |pmid=32129461 |pmc=7253787 |doi=10.1093/biolre/ioaa029 |type= Journal article}}</ref> the formation of a new blood supply, hormones and tissue differentiation. In non-menstruating mammals, decidualization is driven by the embryo, not the mother.<ref name="pmid9618925"/> It evolved in some placental mammals because it confers advantages in that it allows females to prepare for pregnancy without needing a signal from the fetus.<ref name= Emera2012/> Hypothesis&nbsp;3 defers to an explanation of the evolutionary origin of spontaneous decidualization and does not explain the evolution of menstruation alone.<ref name= Emera2012/>
-# Uterine pre-conditioning.<ref name="pmid19136085">{{cite journal |vauthors=Brosens JJ, Parker MG, McIndoe A, Pijnenborg R, Brosens IA |title=A role for menstruation in preconditioning the uterus for successful pregnancy |journal=American Journal of Obstetrics and Gynecology |volume=200 |issue=6 |pages=615.e1–6 |date=June 2009 |pmid=19136085 |doi=10.1016/j.ajog.2008.11.037 }}</ref> This hypothesis claims that a monthly pre-conditioning of the uterus is needed in species, such as humans, that have deeply invasive (deep-rooted) [[placenta]]s. In the process leading to the formation of a placenta, maternal tissues are invaded. This hypothesis holds that menstruation was not evolutionary, rather the result of a coincidental pre-conditioning of the uterus to protect uterine tissue from the deeply rooting placenta, in which a thicker endometrium develops.<ref name="pmid19136085"/> Hypothesis&nbsp;4 does not explain menstruation in non-primates.<ref name=Emera2012/>
+# Uterine pre-conditioning.<ref name="pmid19136085">{{cite journal |vauthors=Brosens JJ, Parker MG, McIndoe A, Pijnenborg R, Brosens IA |title=A role for menstruation in preconditioning the uterus for successful pregnancy |journal=American Journal of Obstetrics and Gynecology |volume=200 |issue=6 |pages=615.e1–6 |date=June 2009 |pmid=19136085 |doi=10.1016/j.ajog.2008.11.037 |type= Journal article}}</ref> This hypothesis claims that a monthly pre-conditioning of the uterus is needed in species, such as humans, that have deeply invasive (deep-rooted) [[placenta]]s. In the process leading to the formation of a placenta, maternal tissues are invaded. This hypothesis holds that menstruation was not evolutionary, rather the result of a coincidental pre-conditioning of the uterus to protect uterine tissue from the deeply rooting placenta, in which a thicker endometrium develops.<ref name="pmid19136085"/> Hypothesis&nbsp;4 does not explain menstruation in non-primates.<ref name=Emera2012/>
 == Notes ==

v t e Human physiology of sexual reproduction
Menstrual cycle	Menarche Menstruation Follicular phase Ovulation Luteal phase
Gametogenesis	Spermatogenesis spermatogonium spermatocyte spermatid sperm Oogenesis oogonium oocyte ootid ovum Germ cell gonocyte gamete
Human sexual activity	Sexual arousal Sexual intercourse Masturbation Erection Penile Clitoral Orgasm Ejaculation Male Female Insemination Fertilization / Fertility Implantation Pregnancy Postpartum period Mechanics of sex Vaginal lubrication
Development of the reproductive system	Sexual differentiation Sexual dimorphism Feminization Virilization Puberty Gonadarche Tanner scale Pubarche Menarche Spermarche Adrenarche Maternal age / Paternal age Menopause
Egg	Ovum Vivipary
Reproductive endocrinology and infertility	Hypothalamic–pituitary–gonadal axis Hypothalamic–pituitary–prolactin axis Andrology Hormone
Breast	Thelarche Development Lactation Breastfeeding
Human reproductive system	Male Female
Diseases and disorders	Anorgasmia Dysorgasmia Dyspareunia Erectile dysfunction Hard flaccid syndrome Premature ejaculation Vaginismus

Authority control databases
International	FAST
National	Spain Germany Israel United States Czech Republic