An analysis by the US National Institutes of Health has provided the strongest evidence to date that nausea and vomiting during pregnancy is associated with a lower risk of miscarriage.
The study was conducted by researchers at NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and other institutions.
Nausea and vomiting that occurs in pregnancy is often called “morning sickness,” as these symptoms typically begin in the morning and usually resolve as the day progresses. For most women, nausea and vomiting subside by the 4th month of pregnancy. Others may have these symptoms for the duration of their pregnancies. The cause of morning sickness is not known, but researchers have proposed that it protects the foetus against toxins and disease-causing organisms in foods and beverages.
“It’s a common thought that nausea indicates a healthy pregnancy, but there wasn’t a lot of high-quality evidence to support this belief,” said the study’s first author, Dr Stefanie N Hinkle, a staff scientist in NICHD’s epidemiology branch. “Our study evaluates symptoms from the earliest weeks of pregnancy, immediately after conception, and confirms that there is a protective association between nausea and vomiting and a lower risk of pregnancy loss.”
For their study, Hinkle and her colleagues analysed data from the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial, in which researchers tested whether taking daily low-dose aspirin prevents women who experienced one or two prior pregnancy losses from experiencing a future loss.
The authors looked at data from all the women in the study who had a positive pregnancy test. The women kept daily diaries of whether they experienced nausea and vomiting in the 2nd through the 8th week of their pregnancies and then responded to a monthly questionnaire on their symptoms through the 36th week of pregnancy. The study authors noted that most previous studies on nausea and pregnancy loss were not able to obtain such detailed information on symptoms in these early weeks of pregnancy. Instead, most of studies had relied on the women’s recollection of symptoms much later in pregnancy or after they had experienced a pregnancy loss.
In the EAGeR trial, a total of 797 women had positive pregnancy tests, with 188 pregnancies ending in loss. By the 8th week of pregnancy, 57.3% of the women reported experiencing nausea and 26.6% reported nausea with vomiting. The researchers found that these women were 50% to 75% less likely to experience a pregnancy loss, compared to those who had not experienced nausea alone or nausea accompanied by vomiting.
Importance: Nausea and vomiting during pregnancy have been associated with a reduced risk for pregnancy loss. However, most prior studies enrolled women with clinically recognized pregnancies, thereby missing early losses.
Objective: To examine the association of nausea and vomiting during pregnancy with pregnancy loss.
Design, Setting, and Participants: A randomized clinical trial, Effects of Aspirin in Gestation and Reproduction, enrolled women with 1 or 2 prior pregnancy losses at 4 US clinical centers from June 15, 2007, to July 15, 2011. This secondary analysis was limited to women with a pregnancy confirmed by positive results of a human chorionic gonadotropin (hCG) test. Nausea symptoms were ascertained from daily preconception and pregnancy diaries for gestational weeks 2 to 8. From weeks 12 to 36, participants completed monthly questionnaires summarizing symptoms for the preceding 4 weeks. A week-level variable included nausea only, nausea with vomiting, or neither.
Main Outcomes and Measures: Peri-implantation (hCG-detected pregnancy without ultrasonographic evidence) and clinically recognized pregnancy losses.
Results: A total of 797 women (mean [SD] age, 28.7 [4.6] years) had an hCG-confirmed pregnancy. Of these, 188 pregnancies (23.6%) ended in loss. At gestational week 2, 73 of 409 women (17.8%) reported nausea without vomiting and 11 of 409 women (2.7%), nausea with vomiting. By week 8, the proportions increased to 254 of 443 women (57.3%) and 118 of 443 women (26.6%), respectively. Hazard ratios (HRs) for nausea (0.50; 95% CI, 0.32-0.80) and nausea with vomiting (0.25; 95% CI, 0.12-0.51) were inversely associated with pregnancy loss. The associations of nausea (HR, 0.59; 95% CI, 0.29-1.20) and nausea with vomiting (HR, 0.51; 95% CI, 0.11-2.25) were similar for peri-implantation losses but were not statistically significant. Nausea (HR, 0.44; 95% CI, 0.26-0.74) and nausea with vomiting (HR, 0.20; 95% CI, 0.09-0.44) were associated with a reduced risk for clinical pregnancy loss.
Conclusions and Relevance: Among women with 1 or 2 prior pregnancy losses, nausea and vomiting were common very early in pregnancy and were associated with a reduced risk for pregnancy loss. These findings overcome prior analytic and design limitations and represent the most definitive data available to date indicating the protective association of nausea and vomiting in early pregnancy and the risk for pregnancy loss.
Stefanie N Hinkle; Sunni L Mumford; Katherine L Grantz; Robert M Silve; Emily M Mitchell; Lindsey A Sjaarda; Rose G Radin; Neil J Perkins; Noya Galai; Enrique F Schisterman