Ondansetron in pregnancy and risk of adverse fetal outcomes.

Ondansetron is frequently used to treat nausea and vomiting during pregnancy, but the safety of this drug for the fetus has not been well studied. We investigated the risk of adverse fetal outcomes associated with ondansetron administered during pregnancy. From a historical cohort of 608,385 pregnancies in Denmark, women who were exposed to ondansetron and those who were not exposed were included, in a 1:4 ratio, in propensity-score-matched analyses of spontaneous abortion (1849 exposed women vs. 7396 unexposed women), stillbirth (1915 vs. 7660), any major birth defect (1233 vs. 4932), preterm delivery (1792 vs. 7168), and birth of infants at low birth weight and small for gestational age (1784 vs. 7136). In addition, estimates were adjusted for hospitalization for nausea and vomiting during pregnancy (as a proxy for severity) and the use of other antiemetics. Receipt of ondansetron was not associated with a significantly increased risk of spontaneous abortion, which occurred in 1.1% of exposed women and 3.7% of unexposed women during gestational weeks 7 to 12 (hazard ratio, 0.49; 95% confidence interval [CI], 0.27 to 0.91) and in 1.0% and 2.1%, respectively, during weeks 13 to 22 (hazard ratio, 0.60; 95% CI, 0.29 to 1.21). Ondansetron also conferred no significantly increased risk of stillbirth (0.3% for exposed women and 0.4% for unexposed women; hazard ratio, 0.42; 95% CI, 0.10 to 1.73), any major birth defect (2.9% and 2.9%, respectively; prevalence odds ratio, 1.12; 95% CI, 0.69 to 1.82), preterm delivery (6.2% and 5.2%; prevalence odds ratio, 0.90; 95% CI, 0.66 to 1.25), delivery of a low-birth-weight infant (4.1% and 3.7%; prevalence odds ratio, 0.76; 95% CI, 0.51 to 1.13), or delivery of a small-for-gestational-age infant (10.4% and 9.2%; prevalence odds ratio, 1.13; 95% CI, 0.89 to 1.44). Ondansetron taken during pregnancy was not associated with a significantly increased risk of adverse fetal outcomes. (Funded by the Danish Medical Research Council.).