Oseltamivir use in pregnancy: Risk of birth defects, preterm delivery, and small for gestational age infants

Influenza infection during pregnancy increases risks for adverse outcomes for both mother and fetus. For this reason, treatment for infection or postexposure prophylaxis with a neuraminidase inhibitor, such as oseltamivir, may be needed.

Between 2009 and 2017, the Organization of Teratology Information Specialists (OTIS) MotherToBaby Pregnancy Studies enrolled pregnant women in the United States and Canada who were or were not treated with oseltamivir in a prospective cohort study. Data were collected on major birth defects, spontaneous abortion, preterm delivery, and small for gestational age birth size. Crude relative risks (RRs) or hazard ratios (HRs) were estimated together with 95% confidence intervals (CIs) for these outcomes.

There were 716 subjects available for analysis; 112 were exposed to oseltamivir sometime in pregnancy and 604 were unexposed. 2/30 (6.7%) first-trimester-exposed pregnancies resulted in a fetus or infant with one or more major birth defects compared to 48/604 (7.9%) in the unexposed cohort (RR 0.84, 95% CI 0.19, 2.80). There were no spontaneous abortions reported. Risk of preterm delivery was not elevated in exposed versus comparison women (HR 0.65, 95% CI 0.26, 1.63). RRs for small for gestational age infants on weight, length, and head circumference following oseltamivir exposure anytime in pregnancy ranged from 0.70 to 1.30 with all 95% CIs including 1.

We found no evidence of increased risks with oseltamivir for any of the outcomes evaluated. While numbers are small, these data are reassuring for pregnant women who need to be treated for infection or for postexposure prophylaxis.