|Classification and external resources|
A miscarriage is the natural death of an embryo or fetus in the womb. It takes place in the early stages of prenatal development prior to fetal viability (the stage of potential independent survival). Among women who know they are pregnant, the miscarriage rate is roughly 15-20% and it is the most common complication of early pregnancy in humans.
- 1 Signs and symptoms
- 2 Causes
- 3 Diagnosis
- 4 Prevention
- 5 Management
- 6 Epidemiology
- 7 Terminology
- 8 Effects
- 9 Other animals
- 10 See also
- 11 References
- 12 External links
Signs and symptoms
The most common symptom of a miscarriage is vaginal bleeding. This can vary from light spotting or brownish discharge to heavy bleeding and bright red blood. The bleeding may come and go over several days. However, light vaginal bleeding is relatively common during the first trimester of pregnancy (the first 12 weeks) and does not necessarily indicate a miscarriage.
Bleeding during pregnancy may be referred to as a threatened miscarriage. Of women who seek clinical treatment for bleeding during pregnancy, about half will miscarry. Symptoms other than bleeding are not statistically related.
Miscarriage may be detected during an ultrasound exam, or through serial human chorionic gonadotropin (HCG) testing. Women pregnant from assisted reproductive technology methods, and women with a history of aborting, may be monitored closely and so detection is sooner than women without such monitoring.
It is estimated about half of early miscarriages will be fully expelled naturally. Several medical options exist for managing documented nonviable pregnancies that have not been expelled naturally, such as medicinal treatment or a dilation and curettage (D&C) procedure. An ERPC, or evacuation of retained products of conception, may be performed to remove the remains of a pregnancy and the placental tissue from the uterus.
Among women who know they are pregnant, the miscarriage rate is roughly 15-20%. Miscarriage may occur for many reasons, not all of which can be identified. Some of these causes include genetic, uterine, or hormonal abnormalities, reproductive tract infections, and tissue rejection. Miscarriage caused by invasive prenatal diagnosis (chorionic villus sampling (CVS) and amniocentesis) is rare (about 1%).
Most clinically apparent miscarriages (two-thirds to three-quarters in various studies) occur during the first trimester. The National Institutes of Health report that "around half of all fertilized eggs die and are lost (aborted) spontaneously, usually before the woman knows she is pregnant."
Chromosomal abnormalities are found in more than half of embryos miscarried in the first 13 weeks. Chromosomal problems due to a parent's genes are, however, a possibility. This is more likely to have been the cause in the case of a woman suffering repeated miscarriages, or if one of the parents has a child or other relatives with birth defects. Genetic problems are more likely to occur with older parents; this may account for the higher rates observed in older women.
Progesterone deficiency may be another cause. Women diagnosed with low progesterone levels in the second half of their menstrual cycle (luteal phase) may be prescribed progesterone supplements, to be taken for the first trimester of pregnancy. No study has shown that general first-trimester progesterone supplements reduce the risk however, (when a mother might already be losing her baby), and even the identification of problems with the luteal phase as a contributing factor has been questioned.
One study found that 19% of second trimester losses were caused by problems with the umbilical cord. Problems with the placenta also may account for a significant number of later-term miscarriages.
Pregnancies of more than one fetus, i.e. twins, triplets, etc., are considered at increased risk. The more fetuses in the womb, the higher the risk
Several intercurrent diseases in pregnancy can potentially increase the risk of miscarriage, including:
- Diabetes mellitus; The risk of miscarriage is increased in women with poorly controlled insulin-dependent diabetes mellitus. This 1998 prospective study found that the risk increased by 3.1% (over the background risk of about 16%) for each standard deviation in glycosylated haemoglobin above the normal range. The risk was not found to be significantly increased in women with good glycaemic control in early pregnancy.
- Polycystic ovary syndrome, which may increase the risk of miscarriage, but this is disputed. Two studies suggested treatment with the drug metformin significantly lowers the rate of miscarriage in women with PCOS, but the quality of these studies has been questioned. A 2006 review of metformin treatment in pregnancy found insufficient evidence of safety, and did not recommend routine treatment with the drug. In 2007 the Royal College of Obstetricians and Gynaecologists also recommended against use of the drug to prevent miscarriage.
- Hypothyroidism; Severe cases of hypothyroidism increase the risk of miscarriage. The effect of milder cases of hypothyroidism on miscarriage rates has not been established. The presence of certain immune conditions such as autoimmune diseases is associated with a greatly increased risk. The presence of anti-thyroid autoantibodies is associated with an increased risk with an odds ratio of 3.73 and 95% confidence interval 1.8–7.6.
- Vertically transmitted infections; Certain vertically transmitted infections (such as rubella and chlamydia) increase the risk.
- Autoimmune disease; Some research suggests autoimmunity as a possible cause of recurrent or late-term miscarriages. Autoimmune disease occurs when the body's own immune system acts against itself. Therefore, in the case of an autoimmune-induced miscarriages the woman's body attacks the growing fetus or prevents normal pregnancy progression. Further research also has suggested that autoimmune disease may cause genetic abnormalities in embryos which in turn may lead to miscarriage. As an example, Celiac disease increases the risk of miscarriage by an odds ratio of approximately 1.4.
Tobacco (cigarette) smokers have an increased risk of miscarriage. An increase in the rates also is associated with the father being a cigarette smoker. The husband study observed a 4% increased risk for husbands who smoke fewer than 20 cigarettes/day, and an 81% increased risk for husbands who smoke 20 or more cigarettes/day.
The age of the mother is a significant risk factor. Miscarriage rates increase steadily with age, with more substantial increases after age 35.
Several other factors have been correlated with higher rates in some research, but whether they cause the miscarriages is debated. No causal mechanism may be known, the studies showing a correlation may have been retrospective (beginning the study after the miscarriages occurred, which may introduce bias) rather than prospective (beginning the study before the women became pregnant), or both. A greater correlation has been shown in the following categories, however.
Nausea and vomiting of pregnancy (NVP, or morning sickness) are associated with a decreased risk. Several proximate causes have been proposed for this relationship, but none are widely agreed upon. NVP is generally interpreted as a defense mechanism which discourages the mother's ingestion of foods that are harmful to the fetus; according to this model, a lower frequency of miscarriage would be an expected consequence of the different food choices made by a women experiencing NVP.
A study of more than 92,000 pregnant women found that most types of exercise (with the exception of swimming) correlated with a higher risk of miscarrying prior to 18 weeks. Increasing time spent on exercise was associated with a greater risk: an approximately 10% increased risk was seen with up to 1.5 hours per week of exercise, and a 200% increased risk was seen with more than 7 hours per week of exercise. However, the study found none of these risks to be statistically significant. High-impact exercise was especially associated with the increased risk. No relationship was found between exercise rates after the 18th week of pregnancy. The majority of miscarriages had already occurred at the time women were recruited for the study, and no information on nausea during pregnancy or exercise habits prior to pregnancy was collected.
Caffeine consumption also has been correlated to miscarriage rates, at least at higher levels of intake. However, such higher rates have been found to be statistically significant only in certain circumstances. A 2007 study of more than 1,000 pregnant women found that those who reported consuming 200 mg or more of caffeine per day experienced a 25% rate, compared to 13% among women who reported no caffeine consumption. 200 mg of caffeine is present in 10 oz (300 mL) of coffee or 25 oz (740 mL) of tea. This study controlled for pregnancy-associated nausea and vomiting (NVP or morning sickness): the increased rate for heavy caffeine users was seen regardless of how NVP affected the women. About half of the miscarriages had already occurred at the time women were recruited for the study. A second 2007 study of approximately 2,400 pregnant women found that caffeine intake up to 200 mg per day was not associated with increased rates (the study did not include women who drank more than 200 mg per day past early pregnancy). A prospective cohort study in 2009 found that light or moderate caffeine consumption (up to 300 mg per day) had no effect on pregnancy or miscarriage rates.
Sexual intercourse during the first trimester has often been said or assumed by doctors to be a cause of miscarriage. However the association has never been proved or disproved.
Loop electrosurgical excision procedure (LEEP) is one of the most commonly used approaches to treat high grade cervical dysplasia. A cohort study came to the result that women with a time interval from LEEP to pregnancy of less than 12 months compared with 12 months or more were at significantly increased risk for spontaneous abortion, with risk of spontaneous abortion of 18% compared with 4.6%, respectively. On the other hand, no increased risk was identified for preterm birth after LEEP.
A miscarriage may be confirmed via obstetric ultrasound and by the examination of the passed tissue. When looking for microscopic pathologic symptoms, one looks for the products of conception. Microscopically, these include villi, trophoblast, fetal parts, and background gestational changes in the endometrium. As many as half the embryos miscarried have a chromosomal abnormality. When chromosomal abnormalities are found in more than one miscarriage, genetic testing of both parents may be done.
A review article in The New England Journal of Medicine based on a consensus meeting of the Society of Radiologists in Ultrasound in America (SRU) has suggested that miscarriage should be diagnosed only if any of the following criteria are met upon ultrasonography visualization:
- Crown-rump length of at least 7 mm and no heartbeat.
- Mean gestational sac diameter of at least 25 mm and no embryo.
- Absence of embryo with heartbeat at least 2 weeks after an ultrasound scan that showed a gestational sac without a yolk sac.
- Absence of embryo with heartbeat at least 11 days after an ultrasound scan that showed a gestational sac with a yolk sac.
In addition, signs upon ultrasonography that are suggested to be suspicious for miscarriage, but not diagnostic of it, include:
- Crown–rump length of less than 7 mm and no heartbeat.
- Mean gestational sac diameter of 16–24 mm and no embryo.
- Absence of embryo with heartbeat 7–13 days after an ultrasound scan that showed a gestational sac without a yolk sac.
- Absence of embryo with heartbeat 7–10 days after a scan that showed a gestational sac with a yolk sac.
- Absence of embryo at least 6 weeks after last menstrual period.
- Amniotic sac seen adjacent to yolk sac, and with no visible embryo.
- Yolk sac of more than 7 mm.
- Small gestational sac compared to embryo size (less than 5 mm difference between mean sac diameter and crown–rump length).
The clinical presentation of a threatened miscarriage describes any bleeding seen during pregnancy prior to viability, that has yet to be assessed further. At investigation it may be found that the fetus remains viable and the pregnancy continues without further problems.
Alternatively the following terms are used to describe pregnancies that do not continue:
- An empty sac is a condition where the gestational sac develops normally, while the embryonic part of the pregnancy is either absent or stops growing very early. Other terms for this condition are blighted ovum and anembryonic pregnancy.
- An inevitable miscarriage describes a condition in which the cervix has already dilated open, but the fetus has yet to be expelled. This usually will progress to a complete miscarriage. The fetal heart beat may have been shown to have stopped, but this is not part of the criteria.
- A complete miscarriage is when all products of conception have been expelled. Products of conception may include the trophoblast, chorionic villi, gestational sac, yolk sac, and fetal pole (embryo); or later in pregnancy the fetus, umbilical cord, placenta, amniotic fluid, and amniotic membrane. The presence of a pregnancy test that is still positive as well as an empty uterus upon transvaginal ultrasonography does, however, fulfill the definition of pregnancy of unknown location. Therefore, there may be a need for e.g. follow-up pregnancy tests to ensure that there is no remaining pregnancy, including any ectopic one.
- An incomplete miscarriage occurs when some products of conception have been passed, but some remains in utero. However, an increased distance between the uterine walls on transvaginal ultrasonography may also simply be an increased endometrial thickness and/or a polyp. The use of power Doppler may be better in confirming the presence of significant retained products of conception in the uterine cavity. In cases of uncertainty, there is a need to exclude an ectopic pregnancy, such as by serial beta-hCG measurements.
- A missed miscarriage is when the embryo or fetus has died, but a miscarriage has not yet occurred. It is also referred to as delayed miscarriage or silent miscarriage.
The following two terms consider wider complications or implications of a miscarriage:
- A septic miscarriage occurs when the tissue from a missed or incomplete miscarriage becomes infected. The infection of the uterus carries risk of spreading infection (septicaemia) and is a grave risk to the life of the woman.
- Recurrent pregnancy loss (RPL) or recurrent miscarriage is the occurrence of three consecutive miscarriages. If the proportion of pregnancies ending in miscarriage is 15% and assuming that miscarriages are independent events, then the probability of two consecutive miscarriages is 2.25% and the probability of three consecutive miscarriages is 0.34%. The occurrence of recurrent pregnancy loss is 1%. A large majority (85%) of women who have had two miscarriages will conceive and carry normally afterward.
The physical symptoms of a miscarriage vary according to the length of pregnancy:
- At up to six weeks only small blood clots may be present, possibly accompanied by mild cramping or period pain.
- At 6 to 13 weeks a clot will form around the embryo or fetus, and the placenta, with many clots up to 5 cm in size being expelled prior to completion of the process. The process may take a few hours or be on and off for a few days. Symptoms vary widely and may include vomiting and loose bowels, possibly due to physical discomfort.
- At more than 13 weeks the fetus may be passed easily from the uterus, however the placenta is more likely to be fully or partially retained in the uterus, resulting in an incomplete miscarriage. The physical signs of bleeding, cramping, and pain may be similar to an early stage abortion, but sometimes more severe and labor-like.
Prevention of miscarriage is mainly based on avoiding or mitigating any risk factors of it. Currently there is no known way to prevent an impending miscarriage. Identifying the cause of the miscarriage may help prevent it from happening again in a future pregnancy. In recurrent miscarriage, various tests are indicated to identify any underlying cause. Vitamin supplementation has not been found to be effective to prevent miscarriage.
Bleeding during early pregnancy is the most common symptom of both impending miscarriage and of ectopic pregnancy. Pain does not strongly correlate with the former, but is a common symptom of ectopic pregnancy. Typically, in the case of blood loss, pain, or both, transvaginal ultrasound is performed. If a viable intrauterine pregnancy is not found with ultrasound, serial βHCG tests should be performed to rule out ectopic pregnancy, which is a life-threatening situation.
If the bleeding is light, making an appointment to see one's doctor is recommended. If bleeding is heavy, there is considerable pain, or there is a fever, then seeking emergency medical attention is recommended.
Whilst bed rest has been advocated in the past to help ensure that a threatened pregnancy might continue, and in one study possibly helped when small subchorionic hematoma had been found on ultrasound scans, the prevailing opinion is that this is of no proven benefit.
No treatment is necessary for a diagnosis of complete miscarriage (so long as ectopic pregnancy is ruled out). In cases of an incomplete miscarriage, empty sac, or missed abortion there are three treatment options:
- With no treatment (watchful waiting), most of these cases (65–80%) will pass naturally within two to six weeks. This path avoids the side effects and complications possible from medications and surgery, but increases the risk of mild bleeding, need for unplanned surgical treatment, and incomplete miscarriage.
- Medical management usually consists of using misoprostol (a prostaglandin, brand name Cytotec) to encourage completion of the natural process. About 95% of cases treated with misoprostol will complete within a few days.
- Surgical treatment is the fastest way to complete the process. It also shortens the duration and heaviness of bleeding, and avoids the physical pain associated with the miscarriage. In cases of repeated spontaneous abortions, D&C is also the most convenient way to obtain tissue samples for karyotype analysis (cytogenetic or molecular), although it is also possible to do with expectant and medical management, including the following techniques:
- Vacuum aspiration, sometimes referred to as dilation and evacuation (D&E), uses aspiration to remove uterine contents through the cervix.
- Dilation and curettage (D&C), which involves dilation (widening/opening) of the cervix and surgical removal of part of the lining of the uterus and/or contents of the uterus by scraping and scooping (curettage). D&C has a higher risk of complications compared to non-surgical treatment, including risk of injury to the cervix (e.g. cervical incompetence) and uterus, perforation of the uterus, and potential scarring of the intrauterine lining (Asherman's syndrome). This is an important consideration for women who would like to have children in the future and want to preserve their fertility and reduce the chance of future pregnancy complications.
In delayed miscarriage
- Gestational sac greater than 30-35mm, embryo larger than ~25mm (corresponding to 9+0 weeks of gestational age): Surgery is recommended. It poses a high risk of pain and bleeding with passage of products of conception. Alternative methods may still be considered.
- Gestational sac 15-35mm, embryo smaller than 25mm (corresponding to between 7 and 9+0 weeks of gestational age): Medication is recommended. Surgery or expectant management may be considered.
- Gestational sac smaller than 15-20mm, corresponding to a gestational age of less than 7 weeks: Expectant management or medication is preferable. The products of conception may be difficult to find surgically with a considerable risk of failed surgical procedure.
In incomplete miscarriage
- Retained products of conception smaller than 15mm: Expectant management is generally preferable. There is a high chance of spontaneous expulsion.
- Retained products of conception measuring between 15 and 20mm: Medical or expectant management are recommended. Surgery should only be considered upon specific indication.
- At retained products of conception measuring over 35 to 50mm, the following measures are recommended:
- Administration of misoprostol to hasten passage of products of conception.
- Admission to inpatient care for observation for a few hours or overnight until the majority of the products of conception has passed and bleeding subsided.
- After apparent failure of misoprostol, a gynecologic examination should be done prior to considering surgical evacuation of the uterus or the patient leaving the hospital.
Determining the precise prevalence of miscarriage is not possible, because a large number of miscarriages occur before pregnancies become established and before women are aware they are pregnant. In addition, women with bleeding in early pregnancy may attend for medical care more often than women not experiencing bleeding. Some studies have attempted to account for this by recruiting women who are planning pregnancies and testing for very early pregnancy, although these would also not be representative of the wider population. A systematic review found that the cumulative risk of miscarriage between 5 and 20 weeks of gestation varied from 11% to 22% in studies assessing miscarriage rates. Up to the 13th week of pregnancy, the risk of miscarriage each week was around 2%, dropping to 1% in week 14 and reducing slowly between 14 and 20 weeks.
The prevalence of miscarriage increases with the age of the mother and the father. In a Danish register-based study where the prevalence of miscarriage was 11%, the prevalence rose from 9% in women at 22 years of age to 84% by 48 years of age.
While miscarriage is a term for early pregnancy loss, it is also frequently known in medical literature as spontaneous abortion. Those born before 24 weeks of gestation rarely survive. However, the designation "fetal death" applies variably in different countries and contexts, sometimes incorporating weight, and gestational age from 16 weeks in Norway, 20 weeks in the US and Australia, 24 weeks in the UK to 26 weeks in Italy and Spain. A fetus that died before birth after this gestational age may be referred to as a stillbirth. Under UK law, all stillbirths should be registered, although this does not apply to miscarriages.
The medical terminology applied to women's experiences during early pregnancy has changed over time. Before the 1980s, health professionals used the phrase "spontaneous abortion" for a miscarriage and "induced abortion" for a willful termination of the pregnancy (abbreviated to TOP). When terminations of pregnancy needed to be hidden, suspicion sometimes surrounded miscarriage, complicating an already sensitive language issue. Research suggests that some women dislike the term spontaneous abortion for miscarriage, some are indifferent and some prefer it. These preferences may reflect cultural differences.
In the late 1980s and 1990s, doctors became more conscious of their language in relation to early pregnancy loss. Some medical authors advocated change to use of "miscarriage" instead of "spontaneous abortion" because they argued this would more respectful to women's feelings and help ease a distressing experience. The change was being recommended by some by the profession in Britain in the late 1990s. In 2005 the European Society for Human Reproduction and Embryology (ESHRE) published a paper aiming to facilitate a revision of nomenclature used to describe early pregnancy events.
Historical analysis of the medical terminology applied to early pregnancy loss in Britain has shown that the use of "miscarriage" (instead of "spontaneous abortion") by doctors only occurred after changes in legislation (in the 1960s) and developments in ultrasound technology (in the early 1980s) allowed them to identify miscarriages. in countries where pregnancy termination remains illegal doctors may still not distinguish between "spontaneous" and "induced" abortions in clinical practice.
|This section needs additional citations for verification. (December 2011)|
Although a woman generally physically recovers from a miscarriage quickly, some struggle to recover emotionally. A questionnaire (GHQ-12 General Health Questionnaire) study following women having miscarried showed that more than half (55%) of them presented with significant psychological distress immediately, while 25% did at 3 months; 18% showed psychological symptoms at 6 months, and 11% at 1 year after miscarriage.
Besides the feeling of loss, a lack of understanding by others is often important. People who have not experienced it themselves may find it difficult to empathize with what has occurred, and how upsetting it may be. This may lead to unrealistic expectations of the parents' recovery. The pregnancy and the miscarriage cease to be mentioned in conversations, often because the subject is too painful. This may make the woman feel particularly isolated. Inappropriate or insensitive responses from medical professionals can add to the distress and trauma experienced, so in some cases attempts have been made to draw up a standard code of practice.
Interaction with pregnant women and newborn children may understandably be painful for parents who have experienced miscarriage. Sometimes this makes interaction with friends, acquaintances, and family very difficult.
Some women gain emotional support and feel less alone in their grief through miscarriage self-help and support groups, and for others, online forums or message boards for pregnancy loss play a role in coping and recovery.
Later cardiovascular disease
There is a significant association between miscarriage and later development of coronary artery disease, but not of cerebrovascular disease. The association does not imply causation, but may be a result of an underlying factor that increases the risk of both.
Miscarriage occurs in all animals that experience pregnancy, though in such contexts it is more commonly referred to as a "spontaneous abortion" (the two terms are synonymous). There are a variety of known risk factors for it in non-human animals. For example, in sheep, it may be caused by crowding through doors, or being chased by dogs. In cows, spontaneous abortion may be caused by contagious disease, such as Brucellosis or Campylobacter, but often can be controlled by vaccination. Other diseases are also known to make animals susceptible. Spontaneous abortion occurs in pregnant prairie voles when their mate is removed and they are exposed to a new male, an example of the Bruce effect, although this effect is seen less in wild populations than in the laboratory. Female mice who had spontaneous abortions showed a sharp rise in the amount of time spent with unfamiliar males preceding the abortion than those who did not abort.
- Susan Storck and A.D.A.M. Inc. "Miscarriage". American Accreditation HealthCare Commission.
- National Coordinating Centre for Women's and Children's Health (UK) (December 2012). "Ectopic Pregnancy and Miscarriage: Diagnosis and Initial Management in Early Pregnancy of Ectopic Pregnancy and Miscarriage". NICE Clinical Guidelines, No. 154. Royal College of Obstetricians and Gynaecologists. Retrieved 4 July 2013.
- Gracia CR, Sammel MD, Chittams J, Hummel AC, Shaunik A, Barnhart KT (2005). "Risk Factors for Spontaneous Abortion in Early Symptomatic First-Trimester Pregnancies". Obstetrics & Gynecology 106 (5, Part 1): 993–9. doi:10.1097/01.AOG.0000183604.09922.e0. PMID 16260517.
- Everett C (1997). "Incidence and outcome of bleeding before the 20th week of pregnancy: Prospective study from general practice". BMJ 315 (7099): 32–4. doi:10.1136/bmj.315.7099.32. PMC 2127042. PMID 9233324.
- Tabor A, Alfirevic Z (2010). "Update on procedure-related risks for prenatal diagnosis techniques.". Fetal diagnosis and therapy 27 (1): 1–7. doi:10.1159/000271995. PMID 20051662.
- Agarwal K, Alfirevic Z (August 2012). "Pregnancy loss after chorionic villus sampling and genetic amniocentesis in twin pregnancies: a systematic review.". Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology 40 (2): 128–34. doi:10.1002/uog.10152. PMID 22125091.
- Rosenthal, M. Sara (1999). "The Second Trimester". The Gynecological Sourcebook. WebMD. Retrieved December 18, 2006.
- Francis O (1959). "An analysis of 1150 cases of abortions from the Government R.S.R.M. Lying-in Hospital, Madras". Journal of obstetrics and gynaecology of India 10 (1): 62–70. PMID 12336441.
- Storck, Susan (2012-11-08). "Miscarriage". National Institute of Health. Retrieved 2013-09-01.
- Kajii T, Ferrier A, Niikawa N, Takahara H, Ohama K, Avirachan S (1980). "Anatomic and chromosomal anomalies in 639 spontaneous abortuses". Human Genetics 55 (1): 87–98. doi:10.1007/BF00329132. PMID 7450760.
- "Miscarriage: Causes of Miscarriage". HealthCentral.com. Retrieved July 26, 2012.taken word-for-word from pp. 347–9 of: "What To Do When Miscarriage Strikes". The PDR Family Guide to Women's Health and Prescription Drugs. Montvale, NJ: Medical Economics. 1994. pp. 345–50. ISBN 1-56363-086-9.
- "Pregnancy Over Age 30". MUSC Children's Hospital. Archived from the original on November 13, 2006. Retrieved December 18, 2006.
- Wahabi HA, Fayed AA, Esmaeil SA, Al Zeidan RA (2007). "Progestogen for treating threatened miscarriage". In Wahabi, Hayfaa A. Cochrane Database of Systematic Reviews (12): CD005943. doi:10.1002/14651858.CD005943.pub2. PMID 22161393.
- Bukulmez O, Arici A (2004). "Luteal phase defect: Myth or reality". Obstetrics and Gynecology Clinics of North America 31 (4): 727–44, ix. doi:10.1016/j.ogc.2004.08.007. PMID 15550332.
- Peng HQ, Levitin-Smith M, Rochelson B, Kahn E (2006). "Umbilical Cord Stricture and Overcoiling Are Common Causes of Fetal Demise". Pediatric and Developmental Pathology 9 (1): 14–9. doi:10.2350/05-05-0051.1. PMID 16808633.
- Mills JL, Simpson JL, Driscoll SG, Jovanovic-Peterson L, Van Allen M, Aarons JH, Metzger B, Bieber FR, Knopp RH, Holmes LB (1988). "Incidence of Spontaneous Abortion among Normal Women and Insulin-Dependent Diabetic Women Whose Pregnancies Were Identified within 21 Days of Conception". New England Journal of Medicine 319 (25): 1617–23. doi:10.1056/NEJM198812223192501. PMID 3200277.
- Boomsma CM, Fauser BC, Macklon NS (January 2008). "Pregnancy complications in women with polycystic ovary syndrome.". Seminars in reproductive medicine 26 (1): 72–84. doi:10.1055/s-2007-992927. PMID 18181085.
- Jakubowicz DJ, Iuorno MJ, Jakubowicz S, Roberts KA, Nestler JE (2002). "Effects of Metformin on Early Pregnancy Loss in the Polycystic Ovary Syndrome". Journal of Clinical Endocrinology & Metabolism 87 (2): 524–9. doi:10.1210/jc.87.2.524. PMID 11836280.
- Khattab S, Mohsen IA, Foutouh IA, Ramadan A, Moaz M, Al-Inany H (2006). "Metformin reduces abortion in pregnant women with polycystic ovary syndrome". Gynecological Endocrinology 22 (12): 680–4. doi:10.1080/09513590601010508. PMID 17162710.
- Royal College of Obstetricians and Gynaecologists (December 2007). "Long-term consequences of polycystic ovarian syndrome". Green-top Guideline No. 27. Royal College of Obstetricians and Gynaecologists. Retrieved 2 July 2013.
- Lilja AE, Mathiesen ER (2006). "Polycystic ovary syndrome and metformin in pregnancy". Acta Obstetricia et Gynecologica Scandinavica 85 (7): 861–8. doi:10.1080/00016340600780441. PMID 16817087.
- van den Boogaard E, Vissenberg R, Land JA, van Wely M, van der Post JA, Goddijn M, Bisschop PH (2011). "Significance of (sub)clinical thyroid dysfunction and thyroid autoimmunity before conception and in early pregnancy: A systematic review". Human Reproduction Update 17 (5): 605–19. doi:10.1093/humupd/dmr024. PMID 21622978.
- Gleicher N, Weghofer A, Barad D (2007). "Female infertility due to abnormal autoimmunity: Frequently overlooked and greatly underappreciated. Part II". Expert Review of Obstetrics & Gynecology 2 (4): 465–75. doi:10.1586/1747422.214.171.1245.
- Gleicher N, Weiner R, Vietzke M (2006). "The impact of abnormal autoimmune function on reproduction: Maternal and fetal consequences". Journal of Autoimmunity 27 (3): 161–5. doi:10.1016/j.jaut.2006.08.003. PMID 17029731.
- Gleicher N, Weghofer A, Barad DH (2011). "Do chromosomally abnormal pregnancies really preclude autoimmune etiologies of spontaneous miscarriages?". Autoimmunity Reviews 10 (6): 361–3. doi:10.1016/j.autrev.2010.12.004. PMID 21195806.
- Tersigni, C.; Castellani, R.; de Waure, C.; Fattorossi, A.; De Spirito, M.; Gasbarrini, A.; Scambia, G.; Di Simone, N. (2014). "Celiac disease and reproductive disorders: meta-analysis of epidemiologic associations and potential pathogenic mechanisms". Human Reproduction Update 20 (4): 582–593. doi:10.1093/humupd/dmu007. ISSN 1355-4786.
- Ness RB, Grisso JA, Hirschinger N, Markovic N, Shaw LM, Day NL, Kline J (1999). "Cocaine and Tobacco Use and the Risk of Spontaneous Abortion". New England Journal of Medicine 340 (5): 333–9. doi:10.1056/NEJM199902043400501. PMID 9929522.
- Venners SA, Wang X, Chen C, Wang L, Chen D, Guang W, Huang A, Ryan L, O'Connor J, Lasley B, Overstreet J, Wilcox A, Xu X (2004). "Paternal Smoking and Pregnancy Loss: A Prospective Study Using a Biomarker of Pregnancy". American Journal of Epidemiology 159 (10): 993–1001. doi:10.1093/aje/kwh128. PMID 15128612.
- Bray I, Gunnell D, Davey Smith G (2006). "Advanced paternal age: How old is too old?". Journal of Epidemiology & Community Health 60 (10): 851–3. doi:10.1136/jech.2005.045179. PMC 2566050. PMID 16973530.
- Furneaux EC, Langley-Evans AJ, Langley-Evans SC (2001). "Nausea and Vomiting of Pregnancy: Endocrine Basis and Contribution to Pregnancy Outcome". Obstetrical and Gynecological Survey 56 (12): 775–82. doi:10.1097/00006254-200112000-00004. PMID 11753180.
- Madsen M, Jørgensen T, Jensen ML, Juhl M, Olsen J, Andersen PK, Nybo Andersen AM (2007). "Leisure time physical exercise during pregnancy and the risk of miscarriage: A study within the Danish National Birth Cohort". BJOG 114 (11): 1419–26. doi:10.1111/j.1471-0528.2007.01496.x. PMC 2366024. PMID 17877774.
- Weng X, Odouli R, Li DK (2008). "Maternal caffeine consumption during pregnancy and the risk of miscarriage: a prospective cohort study". Am. J. Obstet. Gynecol. 198 (3): 279.e1–8. doi:10.1016/j.ajog.2007.10.803. PMID 18221932. Lay summary – The New York Times (January 20, 2008).
- Savitz DA, Chan RL, Herring AH, Howards PP, Hartmann KE (2008). "Caffeine and Miscarriage Risk". Epidemiology 19 (1): 55–62. doi:10.1097/EDE.0b013e31815c09b9. PMID 18091004. Lay summary – Medical News Today (January 23, 2008).
- Pollack AZ, Buck Louis GM, Sundaram R, Lum KJ (2010). "Caffeine consumption and miscarriage: A prospective cohort study". Fertility and Sterility 93 (1): 304–6. doi:10.1016/j.fertnstert.2009.07.992. PMC 2812592. PMID 19732873.
- Moscrop A. Can sex during pregnancy cause a miscarriage? A concise history of not knowing. Br J Gen Pract. 2012 Apr;62(597) e308-10. doi: 10.3399/bjgp12X636164. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3310038/
- "Miscarriage: An Overview". Armenian Medical Network. 2005. Retrieved September 19, 2007.
- Conner SN, Cahill AG, Tuuli MG, Stamilio DM, Odibo AO, Roehl KA, Macones GA (2013). "Interval from loop electrosurgical excision procedure to pregnancy and pregnancy outcomes". Obstet Gynecol 122 (6): 1154–9. doi:10.1097/01.AOG.0000435454.31850.79. PMID 24201682.
- Broy P, Bérard A (2010). "Gestational exposure to antidepressants and the risk of spontaneous abortion: A review". Current drug delivery 7 (1): 76–92. doi:10.2174/156720110790396508. PMID 19863482.
- Nakhai-Pour HR, Broy P, Bérard A (2010). "Use of antidepressants during pregnancy and the risk of spontaneous abortion". Canadian Medical Association Journal 182 (10): 1031–7. doi:10.1503/cmaj.091208. PMC 2900326. PMID 20513781.
- Royal College of Obstetricians and Gynaecologists (RCOG) (April 2011). "The investigation and treatment of couples with recurrent first-trimester and second-trimester miscarriage". Green-top Guideline No. 17. Royal College of Obstetricians and Gynaecologists (RCOG). Retrieved 2 July 2013.
- Doubilet PM, Benson CB, Bourne T, Blaivas M, Barnhart KT, Benacerraf BR, Brown DL, Filly RA, Fox JC, Goldstein SR, Kendall JL, Lyons EA, Porter MB, Pretorius DH, Timor-Tritsch IE (2013). "Diagnostic Criteria for Nonviable Pregnancy Early in the First Trimester". New England Journal of Medicine 369 (15): 1443–1451. doi:10.1056/NEJMra1302417. PMID 24106937.
- Stead, Latha; Stead, S. Matthew; Kaufman, Matthew; Suarez, Luis (2006). First Aid for The Obstetrics and Gynecology Clerkship. New York: McGraw-Hill. p. 138. ISBN 978-0-07-144874-1.
- MedlinePlus (October 25, 2004). "Abortion – incomplete". Medical Encyclopedia. Archived from the original on April 25, 2006. Retrieved May 24, 2006.
- Kirk E, Bottomley C, Bourne T (2013). "Diagnosing ectopic pregnancy and current concepts in the management of pregnancy of unknown location". Human Reproduction Update 20 (2): 250. doi:10.1093/humupd/dmt047. PMID 24101604.
- Farquharson RG, Jauniaux E, Exalto N (2005). "Updated and revised nomenclature for description of early pregnancy events". Human Reproduction 20 (11): 3008–11. doi:10.1093/humrep/dei167. PMID 16006453.
- Hutchon DJ (June 1997). "Missed abortion versus delayed miscarriage.". British journal of obstetrics and gynaecology 104 (6): 753. doi:10.1111/j.1471-0528.1997.tb11994.x. PMID 9197887.
- Royal College of Obstetricians and Gynaecologists (May 2003). "The investigation and treatment of couples with recurrent miscarriage". Green-top Guideline No. 17. Retrieved October 20, 2010.
- www.birth.com.au (October 2004). "miscarriage". Retrieved 0 March 2009. [dead link]
- Rumbold A, Middleton P, Pan N, Crowther CA (Jan 19, 2011). "Vitamin supplementation for preventing miscarriage.". Cochrane database of systematic reviews (Online) (1): CD004073. doi:10.1002/14651858.CD004073.pub3. PMID 21249660.
- Yip SK, Sahota D, Cheung LP, Lam P, Haines CJ, Chung TK (2003). "Accuracy of Clinical Diagnostic Methods of Threatened Abortion". Gynecologic and Obstetric Investigation 56 (1): 38–42. doi:10.1159/000072482. PMID 12876423.
- Condous G, Okaro E, Khalid A, Bourne T (2005). "Do we need to follow up complete miscarriages with serum human chorionic gonadotrophin levels?". BJOG 112 (6): 827–9. doi:10.1111/j.1471-0528.2004.00542.x. PMID 15924545.
- Ben-Haroush A, Yogev Y, Mashiach R, Meizner I (2003). "Pregnancy outcome of threatened abortion with subchorionic hematoma: Possible benefit of bed-rest?". The Israel Medical Association journal 5 (6): 422–4. PMID 12841015.
- Tien JC, Tan TY (2007). "Non-surgical interventions for threatened and recurrent miscarriages". Singapore medical journal 48 (12): 1074–90; quiz 1090. PMID 18043834.
- Kripke C (2006). "Expectant management vs. surgical treatment for miscarriage". American Family Physician 74 (7): 1125–6. PMID 17039747.
- Tang OS, Ho PC (2006). "The use of misoprostol for early pregnancy failure". Current Opinion in Obstetrics and Gynecology 18 (6): 581–6. doi:10.1097/GCO.0b013e32800feedb. PMID 17099326.
- Clinical Practice Guideline: Miscarriage: Management from Royal Women's Hospital. Publication date: 7 October 2010.
- Ammon Avalos L, Galindo C, Li DK (June 2012). "A systematic review to calculate background miscarriage rates using life table analysis.". Birth defects research. Part A, Clinical and molecular teratology 94 (6): 417–23. doi:10.1002/bdra.23014. PMID 22511535.
- Nybo Andersen AM, Wohlfahrt J, Christens P, Olsen J, Melbye M (2000). "Maternal age and fetal loss: Population based register linkage study". BMJ 320 (7251): 1708–12. doi:10.1136/bmj.320.7251.1708. PMC 27416. PMID 10864550.
- Kleinhaus K, Perrin M, Friedlander Y, Paltiel O, Malaspina D, Harlap S (2006). "Paternal Age and Spontaneous Abortion". Obstetrics & Gynecology 108 (2): 369–77. doi:10.1097/01.AOG.0000224606.26514.3a. PMID 16880308.
- Slama R, Bouyer J, Windham G, Fenster L, Werwatz A, Swan SH (2005). "Influence of Paternal Age on the Risk of Spontaneous Abortion". American Journal of Epidemiology 161 (9): 816–23. doi:10.1093/aje/kwi097. PMID 15840613.
- Farquharson RG, Jauniaux E, Exalto N (November 2005). "Updated and revised nomenclature for description of early pregnancy events.". Human reproduction (Oxford, England) 20 (11): 3008–11. doi:10.1093/humrep/dei167. PMID 16006453.
- Mohangoo AD, Blondel B, Gissler M, Velebil P, Macfarlane A, Zeitlin J (2013). "International comparisons of fetal and neonatal mortality rates in high-income countries: should exclusion thresholds be based on birth weight or gestational age?". PLoS ONE 8 (5): e64869. doi:10.1371/journal.pone.0064869. PMC 3658983. PMID 23700489.
- Li, Z; Zeki, R; Hilder, L; Sullivan, EA (2012). "Australia's Mothers and Babies 2010". Perinatal statistics series no. 27. Cat. no. PER 57. Australian Institute of Health and Welfare National Perinatal Statistics Unit, Australian Government. Retrieved 4 July 2013.
- Royal College of Obstetricians and Gynaecologists UK (April 2001). "Further Issues Relating to Late Abortion, Fetal Viability and Registration of Births and Deaths". Royal College of Obstetricians and Gynaecologists UK. Retrieved 4 July 2013.
- https://www.gov.uk/register-stillbirth | date=May 2013
- Moscrop A (2013). "'Miscarriage or abortion?' Understanding the medical language of pregnancy loss in Britain; a historical perspective". Medical Humanities 39 (2): 98–104. doi:10.1136/medhum-2012-010284. PMID 23429567.
- "Standard terminology for reporting of reproductive health statistics in the United States.". Public Health Report 103 (5): 464–71. 1988. PMC 1478116. PMID 3140271.
- Gardner RF (Jul 1, 1972). "Abortion and miscarriage.". British Medical Journal 3 (5817): 51. doi:10.1136/bmj.3.5817.51. PMID 5039574.
- Chalmers B (May 1992). "Terminology used in early pregnancy loss.". British journal of obstetrics and gynaecology 99 (5): 357–8. doi:10.1111/j.1471-0528.1992.tb13746.x. PMID 1622902.
- Beard RW, Mowbray JF, Pinker GD (1985). "Miscarriage or abortion". Lancet 2 (8464): 1122–3. doi:10.1016/S0140-6736(85)90709-3. PMID 2865589.
- Hutchon DJ, Cooper S (1998). "Terminology for early pregnancy loss must be changed". BMJ 317 (7165): 1081. doi:10.1136/bmj.317.7165.1081. PMC 1114078. PMID 9774309.
- Hutchon DJ (1998). "Understanding miscarriage or insensitive abortion: Time for more defined terminology?". American Journal of Obstetrics and Gynecology 179 (2): 397–8. doi:10.1016/S0002-9378(98)70370-9. PMID 9731844.
- Hutchon DJ, Cooper S (Oct 17, 1998). "Terminology for early pregnancy loss must be changed.". BMJ (Clinical research ed.) 317 (7165): 1081. doi:10.1136/bmj.317.7165.1081. PMC 1114078. PMID 9774309.
- Gold KJ, Boggs ME, Mugisha E, Palladino CL (Jan–Feb 2012). "Internet message boards for pregnancy loss: who's on-line and why?". Women's health issues : official publication of the Jacobs Institute of Women's Health 22 (1): e67–72. doi:10.1016/j.whi.2011.07.006. PMID 21907592.
- Lok IH, Yip AS, Lee DT, Sahota D, Chung TK (2010). "A 1-year longitudinal study of psychological morbidity after miscarriage". Fertility and Sterility 93 (6): 1966–75. doi:10.1016/j.fertnstert.2008.12.048. PMID 19185858.
- Miscarriage Standard Code of Practice
- David Vernon (2005). "Having a Great Birth in Australia".[dead link][self-published source?]
- Oliver-Williams CT, Heydon EE, Smith GC, Wood AM (2013). "Miscarriage and future maternal cardiovascular disease: A systematic review and meta-analysis". Heart 99 (22): 1636–1644. doi:10.1136/heartjnl-2012-303237. PMC 3812894. PMID 23539554.
- Spencer, James. Sheep Husbandry in Canada, page 124 (1911).
- "Beef cattle and Beef production: Management and Husbandry of Beef Cattle", Encyclopaedia of New Zealand (1966).
- Fraser-Smith AC (1975). "Male-induced pregnancy termination in the prairie vole, Microtus ochrogaster". Science 187 (4182): 1211–3. doi:10.1126/science.1114340. PMID 1114340.
- Mahady, Scott; Wolff, Jerry (2002). "A field test of the Bruce effect in the monogamous prairie vole (Microtus ochrogaster)". Behavioral Ecology and Sociobiology 52 (1): 31–7. doi:10.1007/s00265-002-0484-0. JSTOR 4602102.
- Becker SD, Hurst JL (2009). "Female behaviour plays a critical role in controlling murine pregnancy block". Proceedings of the Royal Society B 276 (1662): 1723–9. doi:10.1098/rspb.2008.1780. JSTOR 30245000. PMC 2660991. PMID 19324836.
- Miscarriage Association (http://www.miscarriageassociation.org.uk). Provides information and support for women experiencing miscarriage and other early pregnancy problems.
- Pregnancy loss support groups at DMOZ
- UnspokenGrief ™.com | understanding & support for miscarriage survivors. support network
- The causes of recurrent miscarriages in detail