Objective: To study human teratogenic risk of metronidazole.
Design: A case-control analysis of congenital abnormalities after oral metronidazole treatment during pregnancy grouped by months of gestation. The source of information concerning the use of drugs during pregnancy was the prospective data of the women's prenatal logbook and the retrospective data of a questionnaire filled in by mothers.
Setting: The large population-based dataset of the Hungarian Case-Control Surveillance of Congenital Abnormalities, 1980-1991.
Participants: The control group involved 30,663 pregnant women who had healthy babies; the response rate was 65%. The index group consisted of 17,300 pregnant women who had offspring with congenital abnormalities from the study pregnancy; data were available for 82% of these women.
Results: Of 30,663 pregnant women in the control group, 1041 (3.4%) were treated with metronidazole, 162 (0.53%) in the second to third month of gestation. Of 17,300 pregnant women in the index group, 665 (3.8%) were treated with metronidazole, 104 (0.66%) in the second to third months. McNemar analysis for case-matched control pairs indicated a somewhat higher maternal metronidazole treatment in the second-third months of gestation in nine cases with cleft lip with or without cleft palate, but it was not possible to exclude the recall bias. In addition, this finding was not confirmed by the comparison of cases with cleft lip with or without cleft palate and the total control group.
Conclusion: Treatment with oral metronidazole during pregnancy presents no clinically important association with congenital abnormalities.