Prenatal use of metronidazole and birth defects: no association

To determine whether the use of metronidazole by pregnant women increases the risk of birth defects in the offspring.

Two cohorts of pregnant women who delivered live-born or stillborn infants between January 1, 1983 and December 31, 1988 were identified from the Tennessee Medicaid enrollment files. The exposed cohort consisted of 1387 women who filled a prescription for metronidazole between 30 days before and 120 days after the onset of their last normal menstrual period. The unexposed cohort consisted of 1387 comparable women who did not fill a prescription for metronidazole during the same time. Medical records for 94% of the offspring of both study cohorts were then reviewed to ascertain the occurrence of birth defects.

Pregnancy outcomes were similar for the exposed and unexposed cohort members. There was no excess of overall birth defect occurrence in the offspring of exposed women (risk ratio 1.2, 95% confidence interval 0.9-1.6), nor could an excess risk be detected for any category of birth defects.

This study provides no evidence that prenatal use of metronidazole increases the risk of overall birth defect occurrence.