|Classification and external resources|
Morning sickness, also called nausea and vomiting of pregnancy (NVP), nausea gravidarum, emesis gravidarum, and pregnancy sickness, is a pregnancy discomfort that affects more than half of all pregnant women. Symptoms may be present early in the morning and reduce as the day progresses. However, in spite of its common name, nausea and vomiting of pregnancy can occur at any time during the day. For most women the sickness ends around the 12th week of pregnancy.
Related to increased estrogen levels, a similar form of nausea is also seen in some women who use hormonal contraception or hormone replacement therapy. The nausea can be mild or induce actual vomiting, but not severe enough to cause metabolic derangement. In more severe cases, vomiting may cause dehydration, weight loss, high blood pH, and a low level of potassium in the blood. This condition is known as hyperemesis gravidarum and occurs in about 1% of all pregnancies. Nausea and vomiting can be one of the first signs of pregnancy and usually begin around the 6th week of pregnancy (counting gestational age from 14 days before conception).
Proximate causes of pregnancy sickness include:
- Excess salivation during the first trimester, that is often bitter tasting (ptyalism), is then ingested during the mother's sleep.
- An increase in the circulating level of the hormone estrogen. However, there is no consistent evidence of differences in estrogen levels and levels of bilirubin between women that experience sickness and those that do not.
- Low blood sugar due to the placenta's draining energy from the mother, though studies have not confirmed this except for in Type I diabetic expectant mothers.
- An increase in progesterone relaxes the muscles in the uterus, which prevents early childbirth, but may also relax the stomach and intestines, leading to excess stomach acids and gastroesophageal reflux disease.
- An increase in human chorionic gonadotropin. It is probably not the human chorionic gonadotropin itself that causes the nausea. More likely, it is the human chorionic gonadotropin stimulating the maternal ovaries to secrete estrogen, which in turn causes the nausea.
- An increase in sensitivity to odors, which overstimulates normal nausea triggers.
- An increase in bilirubin levels due to increased liver enzymes.
Note that gastroesophageal reflux disease can also be caused by pregnancy, and may result in nausea and vomiting.
Morning sickness is understood as an evolved trait that protects the fetus against toxins ingested by the mother.  Many plants contain chemical toxins that serve as a deterrent to being eaten. Adult humans, like other animals, have defenses against plant toxins, including extensive arrays of detoxification enzymes manufactured by the liver and the surface tissues of various other organs. In the fetus, these defenses are not yet fully developed, and even small doses of plant toxins that have negligible effects on the adult can be harmful or lethal to the embryo. Pregnancy sickness causes women to experience nausea when exposed to the smell or taste of foods that are likely to contain toxins injurious to the fetus, even though they may be harmless to her.
- Morning sickness is very common among pregnant women, which argues in favor of its being a functional adaptation and against the idea that it is a pathology.
- Fetal vulnerability to toxins peaks at around 3 months, which is also the time of peak susceptibility to morning sickness.
- There is a good correlation between toxin concentrations in foods, and the tastes and odors that cause revulsion.
In addition to protecting the fetus, morning sickness may also protect the mother. A pregnant woman's immune system is suppressed during pregnancy, presumably to reduce the chances of rejecting tissues of her own offspring. Because of this, animal products containing parasites and harmful bacteria can be especially dangerous to pregnant women. There is evidence that morning sickness is often triggered by animal products including meat and fish.
If morning sickness is a defense mechanism against the ingestion of toxins, the prescribing of anti-nausea medication to pregnant women may have the undesired side effect of causing birth defects or miscarriages by encouraging harmful dietary choices.
There is unclear evidence about the effectiveness of home treatments for morning sickness.
A number of antiemetics are effective and safe in pregnancy including: pyridoxine/doxylamine, antihistamines (such as diphenhydramine), metoclopramide, and phenothiazines (such as promethazine). With respect to effectiveness it is unknown if one is superior to another. In the United States and Canada, the doxylamine-pyridoxine combination (as Diclegis in US and Diclectin in Canada) is the only approved pregnancy category "A" prescription treatment for nausea and vomiting of pregnancy.
Ondansetron may be beneficial, but there are some concerns regarding an association with cleft palate, and there is little high quality data. Metoclopramide is also used and relatively well tolerated. Evidence for the use of corticosteroids is weak.
Thalidomide was originally developed and prescribed as a cure for morning sickness in West Germany, but its use was discontinued when it was found to cause birth defects. The United States Food and Drug Administration never approved thalidomide for use as a cure for morning sickness.
- Lagiou, P; Tamimi, R; Mucci, LA; Trichopoulos, D; Adami, HO; Hsieh, CC (April 2003). "Nausea and vomiting in pregnancy in relation to prolactin, estrogens, and progesterone: a prospective study". Obstetrics and gynecology 101 (4): 639–44. doi:10.1016/s0029-7844(02)02730-8. PMID 12681864. Retrieved 27 February 2014.
- Elizabeth Bauchner; Wendy Marquez. "Morning Sickness: Coping With The Worst". NY Metro Parents Magazine. Retrieved 2008-07-06.
- Erick, Miriam (2004). Managing Morning Sickness: A Survival Guide for Pregnant Women. Bull Publishing Company. ISBN 0-923521-82-8. Retrieved 2008-07-06.
- "Hypoglycemia in Type 1 Diabetic Pregnancy". Diabetes Care. March 2010. Retrieved 2013-10-02.
- Niebyl, Jennifer R. (2010). "Nausea and Vomiting in Pregnancy". New England Journal of Medicine 363 (16): 1544–1550. doi:10.1056/NEJMcp1003896. PMID 20942670.
- Hook, E. B. (1976). "Changes in tobacco smoking and ingestion of alcohol and caffeinated beverages during early pregnancy: are these consequences, in part, of feto-protective mechanisms diminishing maternal exposure to embryotoxins?". In Kelly, S. Birth Defects: Risks and Consequences. Academic Press. pp. 173–181.
- Profet, Margie (1992). "Pregnancy Sickness as Adaptation: A Deterrent to Maternal Ingestion of Teratogens". In Barkow, John; Cosmides, Jerome; Tooby, Leda. The Adapted Mind: Evolutionary Psychology and the Generation of Culture. Oxford University Press. pp. 327–365.
- Beck, F. (1973). Human Embryology and Genetics. Blackwell Scientific.
- Nesse, Randolphe M; Williams, George C (1996). Why We Get Sick (First ed.). New York: Vintage Books. p. 290.
- Pepper GV, Craig Roberts S (October 2006). "Rates of nausea and vomiting in pregnancy and dietary characteristics across populations". Proceedings of the Royal Society B 273 (1601): 2675–2679. doi:10.1098/rsbp.2006.3633. PMC 1635459. PMID 17002954.
- Chan, Ronna L.; Olshan, A. F.; Savitz, D. A.; Herring, A. H.; Daniels, J. L.; Peterson, H. B.; Martin, S. L. et al. (Sep 22, 2010). "Severity and duration of nausea and vomiting symptoms in pregnancy and spontaneous abortion". Human Reproduction 25 (11): 2907–12. doi:10.1093/humrep/deq260. PMC 3140259. PMID 20861299.
- Sherman, Paul W.; Flaxman, Samuel M. (2002). "Nausea and vomiting of pregnancy in an evolutionary perspective". Am J Obstet Gynecol 186 (5): S190–S197. doi:10.1067/mob.2002.122593. PMID 12011885.
- Haig, David (October 1993). "Genetic conflicts in human pregnancy". Quarterly Review of Biology 68 (4): 495–532. doi:10.1086/418300. PMID 8115596.
- Flaxman, Samuel M.; Sherman, Paul W. (June 2000). "Morning sickness: a mechanism for protecting mother and embryo". Quarterly Review of Biology 75 (2): 113–148. doi:10.1086/393377. PMID 10858967.
- Matthews, A.; Haas, D. M.; O'Mathúna, D. N. P.; Dowswell, T.; Doyle, M. (2014). "Interventions for nausea and vomiting in early pregnancy". The Cochrane Library. doi:10.1002/14651858.CD007575.pub3.
- Jarvis, S; Nelson-Piercy, C (Jun 17, 2011). "Management of nausea and vomiting in pregnancy.". BMJ (Clinical research ed.) 342: d3606. doi:10.1136/bmj.d3606. PMID 21685438.
- Clark SM, Dutta E, Hankins GD (September 2014). "The outpatient management and special considerations of nausea and vomiting in pregnancy". Semin Perinatol. S0146-0005 (14): 00102–5. doi:10.1053/j.semperi.2014.08.014. PMID 25267280.
- Koren, G (October 2012). "Motherisk update. Is ondansetron safe for use during pregnancy?". Canadian family physician Medecin de famille canadien 58 (10): 1092–3. PMC 3470505. PMID 23064917.
- Tan, PC; Omar, SZ (April 2011). "Contemporary approaches to hyperemesis during pregnancy.". Current opinion in obstetrics & gynecology 23 (2): 87–93. doi:10.1097/GCO.0b013e328342d208. PMID 21297474.
- Poon, SL (October 2011). "Towards evidence-based emergency medicine: Best BETs from the Manchester Royal Infirmary. BET 2: Steroid therapy in the treatment of intractable hyperemesis gravidarum.". Emergency medicine journal : EMJ 28 (10): 898–900. doi:10.1136/emermed-2011-200636. PMID 21918097.
- Matthews, A; Dowswell, T; Haas, DM; Doyle, M; O'Mathúna, DP (September 2010). "Interventions for nausea and vomiting in early pregnancy.". The Cochrane database of systematic reviews (9): CD007575. doi:10.1002/14651858.CD007575.pub2. PMID 20824863.
- Borrelli F, Capasso R, Aviello G, Pittler MH, Izzo AA (2005). "Effectiveness and safety of ginger in the treatment of pregnancy-induced nausea and vomiting". Obstetrics and gynecology 105 (4): 849–56. doi:10.1097/01.AOG.0000154890.47642.23. PMID 15802416.
- Tiran, Denise (Feb 2012). "Ginger to reduce nausea and vomiting during pregnancy: Evidence of effectiveness is not the same as proof of safety". Complementary Therapies in Clinical Practice 18 (1): 22–25. doi:10.1016/j.ctcp.2011.08.007. ISSN 1744-3881.