Aim In order to assess whether the use of metronidazole during pregnancy is associated with a higher risk of congenital malformations, a meta-analysis was conducted. Methods All epidemiological studies (cohort and case-control) which estimate risk of congenital malformations after exposure to metronidazole during early pregnancy were included in the meta-analysis. To obtain a summary odds ratio, the MantelHaenszel method was used. A test to verify absence of heterogeneity was also performed. Results One unpublished case-control and four published cohort studies fulfilled the inclusion criteria and were not statistically heterogeneous. A summary odds ratio was calculated for metronidazole exposure during the first trimester: OR=1.08, 95% CI: 0.90-1.29, heterogeneity test x 2 =4.72, P=0.32. ConclusionsThis meta-analysis did not find any relationship between metronidazole exposure during the first trimester of pregnancy and birth defects.