Azithromycin is generally considered safe to take during pregnancy when your doctor determines it’s needed. The FDA classified it as a Category B drug, meaning animal studies showed no risk to the fetus and there’s no evidence of risk in humans. It’s one of the most commonly prescribed antibiotics for pregnant women, particularly for treating chlamydia and certain complications like preterm premature rupture of membranes (PPROM). That said, the safety picture has some nuances worth understanding, especially depending on when during pregnancy you take it.
Why It’s Prescribed During Pregnancy
The most common reason pregnant women receive azithromycin is to treat chlamydia. The CDC recommends a single 1-gram oral dose as the standard treatment for chlamydial infection during pregnancy, noting that clinical experience and published studies support its safety and effectiveness in this context.
Azithromycin also plays a role in managing preterm premature rupture of membranes, a complication where the amniotic sac breaks too early. The American College of Obstetricians and Gynecologists recommends it as an alternative to erythromycin in these cases, and some medical centers have adopted it as their first-choice option. It may also be used as added therapy for cesarean deliveries that occur after labor has started, and for respiratory infections during pregnancy.
Risk of Birth Defects
A large French cohort study published in PLOS Medicine compared first-trimester macrolide antibiotic use (the drug class azithromycin belongs to) against amoxicillin. Overall, macrolide exposure during the first trimester was not associated with an increased risk of major birth defects, with an adjusted risk ratio of 1.00. In plain terms, the overall rate of birth defects was essentially the same as with amoxicillin.
However, two specific findings stood out. Researchers observed a modestly elevated risk of spina bifida (a neural tube defect) and syndactyly (fused fingers or toes) among macrolide-exposed pregnancies as a whole. For azithromycin specifically, one earlier case-control study had flagged a possible link to syndactyly, though it was based on only eight exposed cases. The spina bifida signal for azithromycin alone was weaker and not statistically significant. These are rare conditions to begin with, so even if the association is real, the absolute risk to any individual pregnancy remains very small.
Heart Rhythm Concerns
Azithromycin can affect the heart’s electrical rhythm, a phenomenon called QT prolongation. The FDA issued a boxed warning about the potential risk of fatal heart rhythm problems in people who already have cardiovascular risk factors. For most healthy pregnant women, this isn’t a practical concern, but it’s one reason your provider will consider your full medical history before prescribing it.
Breastfeeding After Delivery
If you’re taking azithromycin around the time of delivery, it does pass into breast milk, but in low amounts. Studies estimate that an infant receives roughly 2 to 3% of the mother’s weight-adjusted dose through nursing. Because azithromycin is also prescribed directly to infants at much higher doses when needed, these trace amounts are not expected to cause problems. In a small study of women who received azithromycin intravenously before cesarean delivery and then breastfed, no adverse events were noted in their infants.
The main things to watch for in a nursing baby are mild digestive effects: loose stools, vomiting, or signs of thrush (a yeast overgrowth that can appear as white patches in the mouth or a persistent diaper rash). These are uncommon and typically mild.
A Specific Risk for Newborns
One concern worth knowing about applies not to taking azithromycin while pregnant, but to giving it directly to a newborn or exposing a very young infant through breast milk in the first weeks of life. Research published through the American Academy of Pediatrics found that infants who received oral azithromycin in the first 14 days of life had an eightfold increase in the odds of developing pyloric stenosis, a condition where the muscle controlling the stomach outlet thickens and blocks food from passing through. The risk dropped but remained elevated (about three times higher than baseline) for infants exposed between 15 and 42 days old. After 42 days, the risk returned to normal.
This finding relates primarily to azithromycin given directly to infants, not to maternal use during pregnancy. A separate study did find that mothers taking a macrolide antibiotic during the first 13 days postpartum while breastfeeding had infants with a 3.5-fold increased risk, though only a small fraction of those prescriptions were for azithromycin. The American Academy of Pediatrics still recommends azithromycin for newborns when it’s truly needed (such as for whooping cough prevention), because the disease risk outweighs the pyloric stenosis risk. But if you’re prescribed azithromycin very close to your due date or shortly after delivery while nursing, it’s worth discussing timing with your provider.
How It Compares to Other Antibiotics
Several antibiotics are considered safe during pregnancy. Penicillin-type drugs like amoxicillin and ampicillin have the longest track record and are often the first choice when they’re effective against the infection being treated. Erythromycin, an older macrolide antibiotic, has also been used extensively in pregnancy, though azithromycin is better tolerated (fewer stomach side effects) and increasingly preferred.
Azithromycin occupies a middle ground: it’s not the most extensively studied antibiotic in pregnancy, but the available evidence is reassuring for most uses. For chlamydia specifically, it’s the recommended treatment because a single dose is effective, which makes it far easier to complete than a multi-day course of an alternative. For other infections, your provider may choose amoxicillin or another penicillin if the bacteria involved are susceptible, reserving azithromycin for situations where it offers a clear advantage.