The Real Reason You Get Morning Sickness When You're Pregnant

Morning sickness during pregnancy is something that most people have heard of, but many underestimate it until it happens to them. According to the Cleveland Clinic, nausea and vomiting take place in roughly 70% of pregnancies. It often starts around the sixth week of pregnancy and fades during the second trimester, but it can last longer for some people. Although it is called "morning sickness," it can flare up at any time of day, potentially interfering with almost every aspect of a person's life, including work (per Women and Birth).

For many people with morning sickness, the condition can be a major deterrent to becoming pregnant again. Some people even consider terminating their pregnancies because of how much distress it causes (per BMC Pregnancy and Childbirth). It is hard to imagine that something so difficult can actually have a positive purpose, but when it comes to morning sickness, that may be just the case — as long as it is not too severe.

A 2016 study published in JAMA Internal Medicine found that among pregnant women with a history of miscarriage, those who experienced nausea and vomiting were 50-75% less likely to miscarry. A 2009 study published in The Journal of Pediatrics also suggests that children of mothers with morning sickness score higher on cognitive tests, including performance IQ and verbal fluency.

Nobody is totally sure why people have morning sickness during pregnancy, but the fact that it is associated with positive outcomes lends credence to the idea that it serves an adaptive function. Neurobiology professor Paul Sherman told the Cornell Chronicle that morning sickness may serve to discourage women from eating foods that could be harmful to their baby. This is supported by data that show morning sickness is more prevalent in societies that consume more alcohol and meat.

On the other hand, for the 3% of people with extreme morning sickness known as hyperemesis gravidarum, any benefits of nausea and vomiting are outweighed by the costs to the mother's health (via the Cleveland Clinic). Hyperemesis gravidarum can lead to dehydration as well as deficiency in electrolytes and nutrition (per BMC Pregnancy and Childbirth). For this reason, the Cleveland Clinic recommends calling your doctor if you lose weight, vomit three or more times a day, or show signs of severe dehydration. Other symptoms that warrant a call to the doctor include dizziness, fainting, extreme tiredness, and a fast heartbeat.