Morning sickness

Morning sickness

Morning sickness
Classification and external resources
Specialty Obstetrics
ICD-10 O21.0
ICD-9-CM 643.0
MedlinePlus 003119

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).


  • Causes 1
    • Defense mechanism 1.1
  • Treatments 2
    • Medications 2.1
    • Alternative medicine 2.2
  • History 3
    • Thalidomide 3.1
  • References 4


Morning sickness

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.[1] 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.[2]
  • 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.[3][4]
  • 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.[5]
  • 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.

Defense mechanism

Morning sickness is understood as an

  1. ^ 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.  
  2. ^ Elizabeth Bauchner; Wendy Marquez. "Morning Sickness: Coping With The Worst". NY Metro Parents Magazine. Retrieved 2008-07-06. 
  3. ^ Erick, Miriam (2004). Managing Morning Sickness: A Survival Guide for Pregnant Women. Bull Publishing Company.  
  4. ^ "Hypoglycemia in Type 1 Diabetic Pregnancy". Diabetes Care. March 2010. Retrieved 2013-10-02. 
  5. ^ Niebyl, Jennifer R. (2010). "Nausea and Vomiting in Pregnancy". New England Journal of Medicine 363 (16): 1544–1550.  
  6. ^ 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. 
  7. ^ 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. 
  8. ^ Beck, F. (1973). Human Embryology and Genetics. Blackwell Scientific. 
  9. ^ a b  
  10. ^ 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.  
  11. ^ 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.  
  12. ^ Sherman, Paul W.; Flaxman, Samuel M. (2002). "Nausea and vomiting of pregnancy in an evolutionary perspective". Am J Obstet Gynecol 186 (5): S190–S197.  
  13. ^  
  14. ^ 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.  
  15. ^ 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.  
  16. ^ a b c Jarvis, S; Nelson-Piercy, C (Jun 17, 2011). "Management of nausea and vomiting in pregnancy.". BMJ (Clinical research ed.) 342: d3606.  
  17. ^ a b 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.  
  18. ^ Koren, G (October 2012). "Motherisk update. Is ondansetron safe for use during pregnancy?". Canadian family physician Medecin de famille canadien 58 (10): 1092–3.  
  19. ^ Tan, PC; Omar, SZ (April 2011). "Contemporary approaches to hyperemesis during pregnancy.". Current opinion in obstetrics & gynecology 23 (2): 87–93.  
  20. ^ 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.  
  21. ^ 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.  
  22. ^ 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.  
  23. ^ 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.  


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.



There is tentative evidence that ginger may be useful; however, it is not clear.[21] Safety concerns have been raised regarding its anticoagulant properties.[22][23]

Alternative medicine

Ondansetron may be beneficial, but there are some concerns regarding an association with cleft palate,[18] and there is little high quality data.[16] Metoclopramide is also used and relatively well tolerated.[19] Evidence for the use of corticosteroids is weak.[20]

A number of antiemetics are effective and safe in pregnancy including: pyridoxine/doxylamine, antihistamines (such as diphenhydramine), metoclopramide, and phenothiazines (such as promethazine).[16][17] With respect to effectiveness it is unknown if one is superior to another.[16] 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.[17]


There is unclear evidence about the effectiveness of home treatments for morning sickness.[15]


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.[9]

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.[13] 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.[14]

Women who have no morning sickness are more likely to miscarry.[11] This may be because such women are more likely to ingest substances that are harmful to the fetus.[12]

  • 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.

There is considerable evidence in support of this theory, including:[9][10]

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. [8]