Taking certain antibiotics during pregnancy may increase your risk of miscarriage

When you’re pregnant and come down with an illness, you’re likely worrying about how the infection could affect your baby. As if that’s not enough, a large study out of the Université de Montréal warns that there are concerns around some of the antibiotics you may need to get better. Researchers found that many antibiotics used to treat infections are associated with an increased risk of miscarriage when taken in early pregnancy.

The study, which was published in the Canadian Medical Association Journal, showed the antibiotics azithromycin, clarithromycin, metronidazole as well as whole classes of antibiotics (sulfonamides, tetracyclines and quinolines) increased the risk of miscarriage when taken before the 20th week of pregnancy. Depending on the drug, the miscarriage risk increased by 65 percent to more than double. The problematic antibiotics are used to treat STIs, skin infections, respiratory infections and more.

But not all antibiotics caused harm. In fact, those that are most often prescribed to treat infections in pregnant women—penicillins and cephalosporins—were not associated with a higher miscarriage rate.

This is not the first study to link antibiotics during pregnancy to miscarriage, but the evidence so far has been mixed. This study, which compared 8,702 women who had clinically diagnosed miscarriages before the 20th week of pregnancy to the medical charts of more than 87,020 women who gave birth, is one the first large studies to offer meaningful results on many of the drugs tested. Researchers found higher numbers of the miscarriage group had taken antibiotics in the first 19 weeks of pregnancy compared to the control group. For example, three percent of women who miscarried were exposed to macrolide antibiotics (including azithromycin and clarithromycin) compared to 1.75 percent of women who gave birth.

Though most antibiotics in the study aren’t typically prescribed during pregnancy (with the exception of penicillins and cephalosporins) because of a lack of research or because smaller studies showed potential connections with miscarriage or birth defects, they are still prescribed from time to time. For example, doctors might recommend them when a safer antibiotic fails to work, or when a woman has an infection that is dangerous to her fetus and the drug is the most effective treatment. In some cases, the antibiotics may be accidentally prescribed to pregnant women before they realize they’re pregnant.

Many factors can contribute to miscarriage, including age, stress and diet, so it’s likely that antibiotics alone are not to blame. And doctors stress that it’s still vitally important to treat infections that develop during pregnancy. “They’re not good for you or the baby,” says study author Anick Bérard, a professor of pharmacy at the Université de Montréal. Many infections, especially ones that aren’t treated early, have been associated with preterm birth and other adverse affects, so it’s important to nip them in the bud.

If your doctor recommends antibiotics in the first half of your pregnancy, ask about the risks. It’s likely the drug you are prescribed will be a penicillin or cephalosporin, which have been shown to be safe. If not, Bérard says this study can offer “one additional piece of information with regards to how to treat infection.”

Read more:
Important precautions for a healthy pregnancy
New study: Antibiotic use during pregnancy may affect baby's gut health
How to treat your cold and flu while pregnant