Use of ondansetron during pregnancy and congenital malformations in the infant

•There are conflicting results on ondansetron and cardiovascular terarotogenicity.•This register based study investigated malformations after use in early pregnancy.•An increased risk for cardiovascular defects, notably septum defects, was observed.•Ondansetron should not be used off label for nausea and vomiting in early pregnancy.•Further prospective studies are needed to clarify possible teratogenicity.

The study investigates teratogenic risks with ondansetron (Zofran®). Data from the Swedish Medical Birth Register combined with the Swedish Register of Prescribed Drugs were used to identify 1349 infants born of women who had taken ondansetron in early pregnancy, 1998–2012. Presence of congenital malformations in the offspring was identified with three national health registers. In a Mantel–Haenszel analysis adjustment was made for year of delivery, maternal age, parity, smoking in early pregnancy and pre-pregnancy body mass index. Risks were expressed as odds or risk ratios with 95% confidence intervals.No statistically significantly increased risk for a major malformation was found. The risks for a cardiovascular defect and notably a cardiac septum defect were increased and statistically significant (OR = 1.62, 95% CI 1.04–2.14, and RR 2.05, 95% CI 1.19–3.28, respective). The teratogenic risk with ondansetron is low but an increased risk for a cardiac septum defect is likely.