The protective effects of nausea and vomiting of pregnancy against adverse fetal outcome--a systematic review.

Unlabelled: Studies have suggested that nausea and vomiting of pregnancy (NVP) may confer favorable pregnancy outcome, when compared to women not experiencing NVP. However, this was never examined systematically.

Methods: We systematically reviewed all human studies examining potential effects of NVP on rates of miscarriage, intrauterine growth restriction, congenital malformations, prematurity and developmental achievements.

Results: Our analysis reveals a consistent favorable effect of NVP on rates of miscarriages, congenital malformations, prematurity, and developmental achievements. The effect size was clinically important for miscarriage, malformations and prematurity. In a few studies the protective effects were more prominent in women with moderate-severe NVP than among those with mild or no NVP.

Conclusions: NVP is associated with favorable fetal outcome, and therefore studies of drug exposure in pregnancy should either match their exposed and control cases for existence and severity of NVP, or adjust for these confounders in their multivariate analysis.