Background:
Metronidazole is used to treat Trichomonas vaginalis and bacterial vaginosis (BV) during pregnancy. Prior studies and meta-analyses of metronidazole have not shown it to be teratogenic or mutagenic in humans, yet there may still be some concerns about its use during pregnancy.

Objective:
We evaluated whether there is an association between metronidazole use during pregnancy and major congenital anomalies.

Method:
A retrospective cohort study was conducted using records from the major Syracuse birth hospital, prenatal visits, and birth certificates. Congenital anomalies were identified at birth or in birth certificates.

Result:
2827 singleton/mother pairs had complete information and were included in this analysis; 894 were exposed to metronidazole during any trimester of pregnancy. Compared to unexposed women, exposed women were more likely to be black (67% vs 40%), under 26 years old (69% vs 51%), smokers (40% vs 30%), and less likely to have had genetic amniocentesis (2% vs 5%) or gestational diabetes (3% vs 6%). The total number of congenital anomalies was 49. Twelve babies (1.3%) exposed during any trimester had anomalies, while 37 unexposed (1.9%) had anomalies. The relative risk of any congenital anomaly with metronidazole exposure in any trimester was 0.70 (95% CI 0.37-1.34). In the group exposed in the first trimester, 4 babies (1.2%) of 329 had anomalies, and the relative risk of anomalies was 0.64 (95% CI 0.23-1.77).

Conclusion:
We found no association between metronidazole use during the first or later trimesters of pregnancy and congenital anomalies.

Implications:
These results support other studies suggesting that metronidazole may be used during pregnancy.