Metronidazole is generally considered safe in pregnancy when it is clearly needed, especially after the first trimester, and major guidelines allow its use to treat infections such as bacterial vaginosis and trichomoniasis during pregnancy. Decisions about using it should always weigh the benefits of treating the infection against small and uncertain potential risks, particularly in early pregnancy.

What studies show

Most human data do not show an increased risk of birth defects, low birth weight, stillbirth, or preterm delivery with metronidazole use in pregnancy. Reviews of thousands of pregnancies also find no evidence that metronidazole is a teratogen (does not appear to cause structural malformations).

Some studies report a higher rate of miscarriage when metronidazole is used in early pregnancy, but it is unclear whether this is due to the drug itself or to the underlying infection being treated. Because of this uncertainty, many manufacturers and clinicians use extra caution with first‑trimester use unless the infection is significant and alternatives are not suitable.

Guideline and expert recommendations

• Public health and professional bodies (such as the CDC and others) support metronidazole for symptomatic bacterial vaginosis and trichomoniasis in pregnancy, as untreated infection itself can increase risks like preterm birth.

• National health services state that metronidazole can be used in pregnancy and that exposure is not a reason to end a pregnancy or to arrange extra fetal monitoring beyond routine care.

Practical points for you

• If you are in the first trimester, many clinicians prefer to use metronidazole only when the infection is clearly significant and alternatives are not appropriate; discuss urgency and options with your obstetric provider.

• If you are in the second or third trimester, metronidazole is typically regarded as low risk when used at standard doses for a short course under medical supervision.

• If you have already taken metronidazole and then discovered you are pregnant, current evidence indicates this alone is not considered a reason for pregnancy termination or extra scans, but you should inform your clinician so they can review your specific situation.

For personal safety, discuss your exact gestation, dose, route (oral, vaginal, topical), and reason for treatment with your maternity or primary‑care provider before starting or stopping the medicine.