During the first trimester of pregnancy, many women experience what’s commonly known as “morning sickness.” As distressing as this nausea and vomiting can be, a team of NIH researchers has gathered some of the most convincing evidence to date that such symptoms may actually be a sign of something very positive: a lower risk of miscarriage.
In fact, when the researchers studied a group of women who had suffered one or two previous miscarriages, they found that the women who felt nauseous during their subsequent pregnancies were 50 to 75 percent less likely to miscarry than those without nausea. While it’s not yet exactly clear what’s going on, the findings lend support to the notion that morning sickness may arise from key biological factors that reflect an increased likelihood of a successful pregnancy.
The study, reported recently in JAMA Internal Medicine , was led by Enrique Schisterman and Stefanie Hinkle of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development. Their findings are based on a secondary analysis of existing data from the recently completed Effects of Aspirin in Gestation and Reproduction (EAGeR) trial. It found that aspirin might help in select cases but is not generally recommended to prevent pregnancy loss .
While other studies have looked at the effects of morning sickness on the risk of miscarriage, most have been limited to pregnancies lost late in the first trimester or thereafter. That’s one of the ways in which the EAGeR study is noteworthy. It enrolled 1,228 women who had one or two previous miscarriages and followed them for up to six menstrual cycles as they tried to become pregnant again. The women, age 18 to 40, used fertility monitors and took daily urine tests to ensure any pregnancy would be detected as early as possible.
A total of 797 women became pregnant. From weeks 2 to 8, women were asked to keep detailed daily diaries of their pregnancies, including whether they had nausea and vomiting. From weeks 12 to 36, the women who remained pregnant (about a quarter of the women miscarried, usually before the end of the first trimester) completed monthly questionnaires to describe their symptoms.
Based on their analysis of the EAGeR data, the researchers found that about 20 percent of the women had already begun to feel nauseous two weeks into their pregnancies. By week 8, the number had climbed to nearly 84 percent, with about 27 percent of the women battling through bouts involving actual vomiting. For the women who experienced nausea only, they were 50 percent less likely to suffer a pregnancy loss on average. Nausea with vomiting in any given week came with a 75 percent reduction in miscarriage risk.
Why would morning sickness be protective of a new pregnancy? The researchers don’t have the answer, and further study is clearly needed to understand the underlying biological mechanisms that might be responsible. One possibility is nausea and vomiting are a sign of increased pregnancy hormones and/or the presence of a healthy placenta to nourish the developing fetus.
Another possibility the researchers considered is that the results reflect the good or bad effects of lifestyle factors on a pregnancy. But no evidence to support this idea was found. They determined that the link between nausea and successful pregnancies persisted even when they factored in differences for reported stress, smoking, and alcohol use in pregnancy.
They also found no support for the popular notion that nausea and vomiting help healthy pregnancies by encouraging women to avoid consuming potential toxins. For instance, whether or not women forego their morning coffee wasn’t a factor in the relationship between nausea and the lower risk for pregnancy loss.
While morning sickness might be a good sign, it doesn’t guarantee a healthy pregnancy. Each pregnancy is different, and the absence of nausea and vomiting shouldn’t be taken as cause for alarm. If you are pregnant and have concerns about your pregnancy, it’s always best to consult with your doctor.
 Association of Nausea and Vomiting During Pregnancy With Pregnancy Loss: A Secondary Analysis of a Randomized Clinical Trial. Hinkle SN, Mumford SL, Grantz KL, Silver RM, Mitchell EM, Sjaarda LA, Radin RG, Perkins NJ, Galai N, Schisterman EF. JAMA Intern Med. 2016 Sep 26. [Epub ahead of print]
 Preconception low-dose aspirin and pregnancy outcomes: results from the EAGeR randomised trial. Schisterman EF, Silver RM, Lesher LL, Faraggi D, Wactawski-Wende J, Townsend JM, Lynch AM, Perkins NJ, Mumford SL, Galai N. Lancet. 2014 Jul 5;384(9937):29-36.
Pregnancy (Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)/NIH)
EAGeR Trial (NICHD/NIH)
Enrique Schisterman (NICHD/NIH)
NIH Support: Eunice Kennedy Shriver National Institute of Child Health and Human Development