This sheet is about exposure to metronidazole in pregnancy and while breastfeeding. This information is based on available published literature. It should not take the place of medical care and advice from your healthcare provider.

What is metronidazole?

Metronidazole is an antimicrobial medication that has been used to treat infections, including vaginal infections. Metronidazole is available in oral, rectal, topical, vaginal and intravenous (I.V.) forms. Flagyl®, Metrogel®, Metrolotion®, and Noritate® are some brand names for metronidazole.

Sometimes when women find out they are pregnant, they think about changing how they take their medication, or stopping their medication altogether. However, it is important to talk with your healthcare providers before making any changes to how you take your medication. Your healthcare providers can talk with you about the benefits of treating your condition and the risks of untreated illness during pregnancy.

I take metronidazole. Can it make it harder for me to get pregnant?

It is not known if metronidazole can make it harder to get pregnant.

Does taking metronidazole increase the chance of miscarriage?

Miscarriage is common and can occur in any pregnancy for many different reasons. It is unlikely that metronidazole would increase the chance of a miscarriage. A study that looked at over 4,000 pregnancies with exposure to metronidazole early in pregnancy did not find an increased chance for miscarriage. A smaller study with 53 pregnancy exposures to metronidazole suggested a greater chance for miscarriage. It is not clear if the miscarriage risk in this study was from the medication or related to the underlying infection that was being treated.

Does taking metronidazole increase the chance of birth defects?

Birth defects can happen in any pregnancy for different reasons. Out of all babies born each year, about 3 out of 100 (3%) will have a birth defect. Research involving over 5,000 women who took metronidazole in pregnancy did not find an increased chance for birth defects.

Does taking metronidazole in pregnancy increase the chance of other pregnancy related problems?

Metronidazole is not expected to increase the chance for other pregnancy-related problems, such as preterm delivery (birth before week 37) or low birth weight (weighing less than 5 pounds, 8 ounces [2500 grams] at birth).

Does taking metronidazole in pregnancy affect future behavior or learning for the child?

Studies have not been done to see if metronidazole can cause behavior or learning issues for the child.

Breastfeeding while taking metronidazole:

Metronidazole passes into breastmilk. The amount of metronidazole that passes into breastmilk can depend on the dose and how the medication is taken (by mouth, by IV, vaginally, or topically). With oral or IV use, the amount of metronidazole in breast milk can be similar to the dose given to infants for treatment. The amounts in breastmilk might be lower with vaginal or topical use, but this is not known. Most babies exposed to metronidazole through breast milk have not had any side effects. If your baby shows symptoms like loose stools, diaper rash, or thrush, contact their healthcare provider.

Some metronidazole product labels have suggested to not breastfeed during treatment and for two days after the last dose. But the benefit of using metronidazole may outweigh possible risks. Your healthcare providers can talk with you about using metronidazole and what treatment is best for you. Be sure to talk to your healthcare provider about all of your breastfeeding questions.

If a man takes metronidazole, could it affect fertility or increase the chance of birth defects?

It is not known if metronidazole could affect male fertility (ability to get a woman pregnant) or increase the chance of birth defects in a partner’s pregnancy. In general, exposures that fathers or sperm donors have are unlikely to increase the risks to a pregnancy. For more information, please see the MotherToBaby fact sheet Paternal Exposures at https://mothertobaby.org/fact-sheets/paternal-exposures-pregnancy/.

Selected References:

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• Burtin P, et al. 1995. Safety of metronidazole in pregnancy: a meta-analysis. Am J Obstet Gynecol 172(21):525-529. [PubMed: 7856680]
• Cantu JM & Garcia-Cruz D. 1982. Midline facial defect as a teratogenic effect of metronidazole. Birth Defects 18:85-88. [PubMed: 7126801]
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