Morning sickness

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Morning sickness, also called nausea, vomiting of pregnancy (emesis gravidarum or NVP), or pregnancy sickness, affects between 50 [1] and 95 percent of all pregnant women as well as some women who use hormonal contraception or hormone replacement therapy. The nausea can be mild or induce actual vomiting. In extreme cases, known as hyperemesis gravidarum, hospitalization may be required to treat the resulting dehydration.

Duration of condition

Morning sickness can occur at any time of the day, though it occurs most often upon waking, because blood sugar levels are typically the lowest after a night without food.

Morning sickness usually starts in the first month of the pregnancy, peaking in the fifth to seventh weeks, and continuing until the 14th to 16th week. For half of the sufferers, it ends by the 16th week of pregnancy. It may take the others up to another month to get relief. Some women suffer intermittent episodes throughout their pregnancy.


There is insufficient evidence to pin down a single (or multiple) cause, but the leading theories for proximate causes include:

As for root causes, this issue is still somewhat controversial. A notable current scientific hypothesis is that morning sickness exists as a safeguard for the embryo's health. Biologists Gillian V. Pepper and S. Craig Roberts have done a study that indicates that the intake of alcohol, sugar, oils, and meat can trigger morning sickness. This then acts as a way of discouraging ingestion of less healthy foods.[2] According to Margie Profet, eating vegetables may be a factor as well.[3] Vegetables produce a small amount of toxins to deter insect infestation and while these toxins are normally harmless to adult humans, they are potentially dangerous to embryos.[4] Additionally, morning sickness begins at the point when the embryo's organ systems are being laid down and the embryo is most vulnerable to birth-defect inducing chemicals, but is growing slowly and has only a modest need for nutrients. By the 14th-16th week, when morning sickness typically wanes, the organ systems of the embryo are mostly complete and the most prominent need is now nutrients. Women afflicted by morning sickness typically avoid "bitter, pungent, highly-flavored, and novel foods," foods which are likely to contain toxins. Foraging people are at an unusually high risk of ingesting plant toxins, due to wild plants being a substantially larger part of their diet than agricultural or industrial people's. Thus, morning sickness offers an evolutionary advantage, as studies have shown that women with more severe morning sickness have less chance to miscarry as well as less chance to have children with birth defects (see below), which explains its prevalence among most women and why it is a universal phenomenon across the human race.

Many other non-scientific theories for morning sickness have been proposed in the past. Notably, according to psychologist Sigmund Freud, morning sickness is the result of the mother's loathing of her husband. The subconscious manifestation of this is a desire to abort the fetus through vomiting.[4] In general, such theories are not accepted by modern scientists.


Treatments for morning sickness typically aim to lessen the symptoms of nausea, rather than attacking the root cause(s) of the nausea. Treatments include:

A doctor may prescribe anti-nausea medications if the expectant mother suffers from dehydration or malnutrition as a result of her morning sickness, a condition known as hyperemesis gravidarum. In the US, Zofran (ondansetron) is the usual drug of choice, though the high cost is prohibitive for some women; in the UK, older drugs with which there is a greater experience of use in pregnancy are preferred, with first choice being promethazine otherwise as second choice metoclopramide, or prochlorperazine.[7]

Thalidomide tragedy

Thalidomide was originally developed and prescribed as a cure for morning sickness in Great Britain, but its use was discontinued when the drug's teratogenic properties came to light. The United States Food and Drug Administration never approved thalidomide for use as a cure for morning sickness.


A recent Canadian survey conducted by researchers at the University of British Columbia and the University of Victoria suggested that the use of medical marijuana may be effective in combating morning sickness,[8] although the researchers noted that their survey was not conclusive.[9]

Associations with miscarriage risk

Studies have shown that women who suffer from morning sickness are less likely to have miscarriages as well as less likely to give birth to a baby with birth defects.[4] Other doctors disagree with these links and claim that the mother's sensitivity to the changes in her body is not a variable that indicates risk of miscarriage.[citation needed] It is also mentioned that many women having a molar pregnancy or an ectopic pregnancy suffer strong nausea.


  1. American Pregnancy Association. "Morning Sickness". Retrieved 2007-04-08.
  2. Gillian V. Pepper and S. Craig Roberts "Rates of nausea and vomiting in pregnancy and dietary characteristics across populations" from Proceedings of The Royal Society "Rates of nausea and vomiting in pregnancy were correlated with high intake of macronutrients (kilocalories, protein, fat, carbohydrate), as well as sugars, stimulants, meat, milk and eggs, and with low intake of cereals and pulses... However, factor analysis of dietary components revealed one factor significantly associated with NVP rate, which was characterized by low cereal consumption and high intake of sugars, oilcrops, alcohol and meat. The results provide further evidence for an association between diet and NVP prevalence across populations, and support for the idea that NVP serves an adaptive prophylactic function against potentially harmful foodstuffs."
  3. Profet, Margie. (1992) Pregnancy sickness as adaptation: a deterrent to maternal ingestion of teratogens.
  4. 4.0 4.1 4.2 Pinker, Steven (1997). How the Mind Works. New York: W. W. Norton & Company, Inc. ISBN 0-393-31848-6.
  5. Borrelli, Francesca et al. "Effectiveness and Safety of Ginger in the Treatment of Pregnancy-Induced Nausea and Vomiting," Obstetrics & Gynecology. September 1, 2005; 106(3): 640 - 641.
  6. Warhus, Susan. "Tips to ease pregnancy's morning sickness". Retrieved 2007-03-05.
  7. British National Formulary (2003). "4.6 Drugs used in nausea and vertigo - Vomiting of pregnancy". "BNF" (45 ed.). Unknown parameter |month= ignored (help)
  8. Westfall R, Janssen P, Lucas P, Capler R (2006). "Survey of medicinal cannabis use among childbearing women: patterns of its use in pregnancy and retroactive self-assessment of its efficacy against 'morning sickness'". Complement Ther Clin Pract. 12 (1): 27–33. PMID 16401527.
  9. Tom Blackwell (2006-01-17). "More pregnancy highs than lows". National Post. Retrieved 2006-06-07. Check date values in: |date= (help)

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