Expecting a Baby, Facing a Bacterial Infection: What the Evidence Says About Azithromycin During Pregnancy

A bacterial infection during pregnancy places expecting mothers in an uncomfortable position: the infection itself may pose risks to the developing fetus, yet so might the medications used to treat it. Azithromycin, one of the most widely prescribed antibiotics in the United States, frequently enters this conversation. Whether a pregnant patient is being treated for a respiratory tract infection, a sexually transmitted infection such as chlamydia, or another bacterial condition, understanding the safety profile of this drug is not merely academic — it is essential.

This article draws on available clinical data, regulatory guidance, and established medical practice to help expecting mothers and their caregivers navigate this nuanced terrain.

The Old Framework: What FDA Pregnancy Categories Used to Tell Us

For decades, the U.S. Food and Drug Administration classified drugs according to pregnancy categories — letters ranging from A to X that summarized fetal risk based on available evidence. Azithromycin was historically assigned to Category B, a designation indicating that animal reproduction studies had not demonstrated fetal risk and that no adequate, well-controlled studies in pregnant women had confirmed harm.

It is important to note that the FDA formally retired this letter-based system in 2015, replacing it with the Pregnancy and Lactation Labeling Rule (PLLR). Under the updated framework, drug labels now include narrative summaries of human and animal data, clinical considerations, and risk-benefit context. For patients accustomed to the old letter grades, this shift can feel disorienting — but the new system actually provides richer, more actionable information.

For azithromycin specifically, the contemporary label language acknowledges limited human data while noting that available studies have not established a clear pattern of birth defects or consistent fetal harm. That said, absence of definitive evidence of harm is not the same as a confirmed safety record, and this distinction matters enormously in clinical decision-making.

What the Research Actually Shows

The body of human evidence on azithromycin in pregnancy is imperfect but informative. Several large observational studies and pharmacovigilance databases have examined outcomes in pregnant women who received azithromycin, particularly during the first trimester when organogenesis — the formation of fetal organs — is most active.

A frequently cited concern involves a 2021 Danish registry study published in JAMA Internal Medicine, which identified associations between first-trimester macrolide antibiotic use (including azithromycin) and a modestly elevated risk of certain birth defects, as well as spontaneous abortion. The findings generated considerable attention in both medical and lay media. However, subsequent analyses and reviews have urged caution in interpreting these results, pointing to methodological limitations including confounding by indication — the underlying infections for which antibiotics were prescribed may themselves contribute to adverse outcomes, making it difficult to isolate the drug's effect.

Conversely, azithromycin has an established and guideline-supported role in treating chlamydia during pregnancy, where the consequences of untreated infection — including preterm labor, low birth weight, and neonatal eye and lung infections — are well-documented. In these contexts, the calculus often favors treatment.

Trimester-Specific Considerations

The timing of antibiotic exposure during pregnancy is not a trivial detail. Each trimester carries its own biological landscape and corresponding risk profile.

First Trimester The first twelve weeks represent the period of greatest fetal vulnerability, as the foundational structures of organs, limbs, and the central nervous system are being established. The contested observational data mentioned above applies primarily to this window. Most clinicians approach first-trimester antibiotic prescribing with heightened caution, reserving treatment for infections where the risk of non-treatment clearly outweighs uncertainty about drug exposure.

Second Trimester Organogenesis is largely complete by the second trimester, which generally reduces — though does not eliminate — concerns about structural birth defects from drug exposure. Many providers consider the second trimester a somewhat safer window for treating bacterial infections when necessary. Azithromycin prescribed during this period for indicated conditions is generally considered a reasonable option in clinical practice.

Third Trimester The final trimester introduces different considerations, including the potential for drug transfer to the fetus through the placenta and implications for the newborn's own physiological systems. Azithromycin does cross the placenta, and while neonatal exposure has not been associated with a consistent pattern of harm, the question remains an active area of inquiry. Preterm labor risk from untreated infections also becomes a pressing concern during this period.

Azithromycin and Breastfeeding

For mothers who continue or initiate antibiotic therapy postpartum, azithromycin does pass into breast milk, though concentrations are relatively low. Available data suggest that the drug is unlikely to cause significant adverse effects in healthy, full-term nursing infants. The American Academy of Pediatrics has historically regarded azithromycin as compatible with breastfeeding, though clinicians should be consulted for individualized guidance, particularly when nursing premature or immunocompromised infants.

The Conversation Every Pregnant Patient Should Have

No article — regardless of how thoroughly it reviews the literature — can substitute for a direct conversation with a qualified healthcare provider. Pregnant patients who are prescribed or considering azithromycin should feel empowered to ask specific questions, including:

• Why is azithromycin being recommended over alternative antibiotics? In some cases, other agents with longer safety records in pregnancy, such as amoxicillin or cephalexin, may be appropriate alternatives depending on the infection type and the patient's allergy history.
• What are the risks of leaving this infection untreated? Understanding the comparative risk of the infection itself often reframes the antibiotic conversation entirely.
• Are there any monitoring steps recommended during or after treatment? Some providers recommend follow-up testing or fetal monitoring depending on the clinical context.
• How does my gestational age affect this decision? Trimester matters, and a provider should be able to explain how timing factors into their recommendation.

Patients should also disclose any other medications they are taking, including supplements and over-the-counter products, as azithromycin can interact with certain cardiac medications and other drugs that affect heart rhythm — a consideration that does not disappear during pregnancy.

Balancing Caution With Clinical Reality

It would be a disservice to pregnant patients to present azithromycin as categorically dangerous, just as it would be irresponsible to dismiss the genuine uncertainties in the literature. The honest answer — the one that most accurately reflects current medical science — is that azithromycin occupies a middle ground: a drug with a generally acceptable safety profile that nonetheless warrants individualized, context-specific evaluation in pregnancy.

For many conditions, particularly sexually transmitted bacterial infections, the evidence supporting treatment during pregnancy is robust and the guidelines are clear. For other applications, particularly during the first trimester, the picture is less settled, and shared decision-making between patient and provider becomes even more critical.

At ZithromaxAll, our commitment is to provide expecting mothers with accurate, evidence-grounded information that supports — rather than replaces — the clinical relationships that are central to safe pregnancy care. If you are pregnant and have been prescribed azithromycin, or if you are considering seeking treatment for a bacterial infection, bring this information to your next prenatal appointment and engage your provider in a candid, informed discussion. The evidence is complex, but the conversation does not have to be.

This article is intended for informational purposes only and does not constitute medical advice. Pregnant individuals should always consult a licensed healthcare provider before starting, stopping, or modifying any medication regimen.