Metronidazole and Pregnancy
Although animal studies on pregnancy and metronidazole have failed to show that the drug causes problems, there is some concern that exposure to the antibiotic might increase the risk of childhood cancers. If you become pregnant while taking the medication, your healthcare provider will weigh the benefits and potential risks in your situation before making a recommendation.
Metronidazole (Flagyl®, MetroCream®, MetroGel®, MetroGel-Vaginal®, MetroLotion®, Noritate®, Vandazole®) is a prescription antibiotic. Even though it is a pregnancy Category B medication, it is not clear if it is safe for use during pregnancy. There is some concern about the carcinogenic (cancer-causing) potential of metronidazole when used by pregnant women.
The U.S. Food and Drug Administration (FDA) uses a category system to classify the possible risks to a fetus when a specific medicine is taken during pregnancy. Pregnancy Category B is given to medicines that have not been adequately studied in pregnant humans but that do not appear to cause harm to the fetus in animal studies.
Metronidazole crosses the placenta. In general, animal studies have failed to show that the drug causes problems during pregnancy, although one study suggested that when injected into the abdominal cavity, the medication might cause miscarriages. Surveys and other similar types of studies in humans seem to suggest that metronidazole probably does not cause birth defects.
There is some concern that exposure to metronidazole during pregnancy might increase the risk of childhood (or even adult) cancers. Metronidazole increases the risk of certain cancers in mice and rats; it is unknown if the same is true for humans. Studies have failed to consistently show that exposure does or does not increase the risk of childhood cancers.