Objective: Our purpose was to determine from published experience in humans whether metronidazole exposure during the first trimester of pregnancy is associated with an increased teratogenic risk.
Study design: All published articles reporting on metronidazole use during pregnancy were screened by two independent reviewers to select those including pregnant patients exposed during the first trimester and comparing the outcomes of their pregnancies with that of patients either not exposed to metronidazole or exposed only during the third trimester. The outcome under consideration was the occurrence of birth defects in live-born infants. The overall odds ratios of first-trimester exposure versus no first-trimester exposure was calculated by combining the selected studies in a meta-analysis according to the procedure of Mantel and Haenszel.
Results: From 32 identified studies, 7 met the inclusion criteria for meta-analysis. Six were prospective and included 253 women exposed to the drug in the first trimester of pregnancy; one was retrospective and reported on 1083 exposed women. The overall weighted odds ratio of exposure versus no exposure during the first trimester calculated by meta-analysis of the 7 studies was 0.93 (95% confidence interval 0.73 to 1.18). The odds ratio calculated from the 6 prospective studies was 1.02 (95% confidence interval 0.48 to 2.18).
Conclusion: Metronidazole does not appear to be associated with an increased teratogenic risk.