Is Penicillin Safe During Pregnancy?

What does the evidence say about penicillin during pregnancy?

1. Across the studies MotherToBaby reviewed, penicillin G hasn't been linked to a chance of birth defects any higher than the 3 to 5 percent baseline every pregnancy carries, and it isn't expected to raise the chance of miscarriage either. 1
2. The rare but serious risk with any penicillin is a severe allergic reaction, which can affect blood flow to the pregnancy, so providers ask about prior reactions before prescribing it and watch closely if you have a known penicillin allergy history. 2
3. Oral penicillin V is the form typically prescribed for strep throat, other upper-respiratory infections, and dental infections like gingivitis, and it carries the older FDA pregnancy category B rating, reflecting a favorable safety profile in available data. 3
4. LactMed data on penicillin V during breastfeeding found only small amounts reach breast milk, roughly 50 micrograms per kilogram of the baby's weight per day, and calls it acceptable for nursing mothers, though a small study noted occasional loose stools or a mild rash in exposed infants. 4
5. A 2025 review of antibiotic safety in pregnancy uses penicillin as a comparison benchmark: one UK study cited in the review found macrolide antibiotics carried a significantly higher chance of major birth defects and heart malformations than penicillin-class antibiotics did. 5

Is penicillin safe in each trimester?

• First trimester. Oral penicillin for a first-trimester infection like strep throat is one of the more reassuring antibiotic choices, since decades of use haven't shown a clear rise in birth defects. Your provider will still confirm you don't have a penicillin allergy history before prescribing it, since a serious allergic reaction is the main risk to watch for at any stage of pregnancy.
• Second trimester. The second trimester is typically the most straightforward window for oral penicillin, and it's a common option for strep throat, dental infections, or other outpatient bacterial infections. Finish the full course your provider prescribes, even once symptoms ease, so the infection has less chance of returning.
• Third trimester. Oral penicillin for a strep throat or dental infection remains a reasonable option in the third trimester too. Note that this page covers outpatient oral use only: the IV penicillin some providers use during labor for Group B strep is a distinct clinical scenario with its own dosing and timing, covered in our separate Group B strep guide.