Azithromycin and Pregnancy: What Expectant Mothers Need to Know

When you're pregnant, every pill, every dose, every medication feels like a big decision. You don’t want to risk your baby’s health, but you also don’t want to suffer through an infection that won’t go away. That’s where azithromycin comes in - a common antibiotic many doctors turn to when treating infections during pregnancy. But is it truly safe? What does the science say? And when should you say yes - or no?

What is azithromycin?

Azithromycin is a macrolide antibiotic. It’s sold under brand names like Zithromax and Zmax, and it’s used to treat bacterial infections like chlamydia, sinus infections, bronchitis, and some types of pneumonia. It works by stopping bacteria from making proteins they need to grow and multiply. Unlike some antibiotics that kill bacteria outright, azithromycin slows them down, letting your immune system finish the job.

One big reason doctors like it is that it’s often taken as a single dose or just for a few days. That’s easier than a 7- to 10-day course of pills - especially when you’re tired, nauseous, or just overwhelmed by pregnancy. It’s also less likely to upset your stomach compared to other antibiotics like amoxicillin or clindamycin.

Is azithromycin safe during pregnancy?

The short answer: yes, it’s generally considered safe. Multiple large studies, including ones from the U.S. Centers for Disease Control and Prevention (CDC) and the MotherToBaby program, have looked at thousands of pregnant women who took azithromycin. None found a clear link between azithromycin and birth defects, miscarriage, or preterm birth.

A 2020 study published in the British Medical Journal followed over 1.4 million pregnancies. Of those, about 15,000 women took azithromycin in the first trimester. The risk of major birth defects was no higher than in women who didn’t take it. Another study from 2022 in Obstetrics & Gynecology looked at 12,000 pregnant women with chlamydia. Those treated with azithromycin had lower rates of preterm delivery and low birth weight than those left untreated.

That’s important. Sometimes, the infection itself is more dangerous than the medicine. Untreated chlamydia, for example, can lead to miscarriage, early labor, or infections in the newborn. So treating it isn’t just about feeling better - it’s about protecting your baby.

When is azithromycin prescribed during pregnancy?

Doctors don’t hand out antibiotics like candy. They prescribe azithromycin only when there’s a clear bacterial infection. Common reasons include:

• Chlamydia - one of the most common STIs in pregnant women. Left untreated, it can cause eye and lung infections in newborns.
• Group B strep (GBS) - sometimes used as a backup if penicillin isn’t an option.
• Respiratory infections - like bacterial bronchitis or sinusitis that don’t improve with rest and fluids.
• Skin or soft tissue infections - such as cellulitis or abscesses.

It’s not used for viral infections like the flu or common cold. Antibiotics don’t work on viruses. Taking them anyway doesn’t help - and might even cause harm by disrupting your gut bacteria or encouraging antibiotic resistance.

How does azithromycin affect the baby?

Azithromycin crosses the placenta, which means some of it reaches your baby. That sounds scary, but it’s not unusual. Many medications do. The key question is: does it cause harm?

Studies show that azithromycin doesn’t accumulate in fetal tissue at dangerous levels. It’s also not known to damage developing organs like the heart, brain, or limbs. The FDA classifies it as Category B - meaning animal studies showed no risk, and human studies haven’t shown harm.

Some parents worry about hearing loss or liver problems in babies. There’s a single 2019 case report that linked high-dose azithromycin to infant liver issues, but that was in a baby born to a mother with severe liver disease and multiple other risk factors. No large study has repeated this finding.

One thing to watch: azithromycin can cause mild diarrhea or upset stomach in the mother. That’s usually temporary. If your baby has loose stools after birth, it’s more likely from changes in your gut bacteria than from the antibiotic itself.

What about the first trimester?

The first trimester is when your baby’s organs are forming - so it’s natural to worry. But azithromycin doesn’t appear to interfere with that process. The largest studies include women who took it as early as week 5 of pregnancy, and no pattern of birth defects emerged.

One myth: azithromycin causes heart defects. That idea came from a 2017 study that suggested a possible link between macrolides and heart problems. But that study didn’t separate azithromycin from other macrolides like erythromycin, which is known to carry a slightly higher risk. When researchers looked at azithromycin alone, the risk disappeared.

So if you’re prescribed azithromycin at 8 weeks pregnant, don’t panic. Talk to your doctor, yes - but don’t refuse treatment out of fear. The benefits almost always outweigh the risks.

Side effects and what to watch for

Most women tolerate azithromycin well. But like any medicine, it can cause side effects:

• Upset stomach or nausea
• Diarrhea
• Headache
• Mild rash

These are usually mild and go away on their own. If you get severe diarrhea (watery or bloody), abdominal cramps, or signs of an allergic reaction - like swelling, hives, or trouble breathing - stop the medicine and call your doctor right away.

There’s also a rare risk of irregular heartbeat, especially if you already have heart problems or take other drugs that affect your heart rhythm. If you’ve ever had QT prolongation or arrhythmia, tell your doctor before taking azithromycin.

What if I’m allergic to penicillin?

Many pregnant women are allergic to penicillin - and that’s where azithromycin shines. It’s a common alternative for treating infections like chlamydia, syphilis (in combination with other drugs), or certain respiratory infections when penicillin isn’t safe.

It’s not the only option - clindamycin and erythromycin are others - but azithromycin is often preferred because it’s easier to take (fewer doses) and has fewer stomach side effects than erythromycin.

Can I breastfeed while taking azithromycin?

Yes. Azithromycin passes into breast milk in very small amounts. Studies show babies get less than 1% of the mother’s dose. No serious side effects have been reported in nursing infants. Some babies might have looser stools or mild fussiness, but that’s rare.

If you’re breastfeeding and your baby develops diarrhea, vomiting, or a rash after you start the medicine, mention it to your pediatrician. But don’t stop breastfeeding unless advised. The benefits of breast milk far outweigh the tiny risk.

What if I took azithromycin before knowing I was pregnant?

This happens more often than you think. Many women get sick with a sinus infection or UTI and take antibiotics without realizing they’re pregnant.

If you took azithromycin in early pregnancy and didn’t know you were pregnant, don’t panic. There’s no evidence it causes harm. Your doctor may suggest a detailed anatomy scan around week 20 to check your baby’s development - but that’s routine for all pregnancies, not because of the antibiotic.

Many women have taken azithromycin before realizing they were pregnant - and gone on to have perfectly healthy babies.

What are the alternatives?

Not every infection needs azithromycin. Here are other antibiotics commonly used in pregnancy:

Penicillin and amoxicillin are usually the first choice because they’ve been used safely for decades. But if you’re allergic, azithromycin is a top-tier alternative.

What should I do if I’m prescribed azithromycin?

Here’s what to do:

1. Confirm the diagnosis. Ask: Is this a bacterial infection? Antibiotics don’t work on viruses.
2. Ask why azithromycin was chosen. Is it because you’re allergic to penicillin? Or because it’s easier to take?
3. Follow the dosage exactly. Don’t skip doses. Don’t stop early, even if you feel better.
4. Take it with food if it upsets your stomach.
5. Keep track of any side effects. Write them down so you can report them at your next visit.
6. Don’t take any other meds - including herbal supplements - without checking with your doctor.

And remember: you’re not alone. Thousands of pregnant women take azithromycin every year. Most have no problems. The goal isn’t to avoid all medication - it’s to treat infections safely so both you and your baby stay healthy.

Frequently Asked Questions