Antibiotic Use During Early Pregnancy Linked to Miscarriage

A recent study finds a link between antibiotic use early on in pregnancy and miscarriage risk—but not all antibiotic classes carry the same risk.

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Could the medicines that help you feel better do harm to your baby? That's what a new study published in the Canadian Medical Association Journal theorizes: Antibiotic use during the early part of pregnancy can double a woman's risk of miscarrying.

Researchers from Canada studied data from the Quebec Pregnancy Cohort, including 8,702 spontaneous abortion cases, and found that 16.8 percent of the miscarriages involved antibiotic use. They contrasted this to the study's control group, which was composed of 87,020 women who did not miscarry—this group only had a 12.6 percent rate of antibiotic exposure. These findings led researchers to believe this exposure could cause as much as a two-fold increase in miscarriage risk

But not all antibiotics showed this same risk: Certain antibiotic classes (including macrolides, quinolones, tetracyclines, sulfonamides and metronidazole) were associated with an increased risk of miscarraige. Erythromycin and nitrofurantoin (which is commonly used to treat urinary tract infections in pregnant patients) were not. 

Before you panic, keep this in mind: Treating infections with antibiotics is sometimes necessary—and leaving the infection without treatment can also present dangers for your baby. Some of these antibiotic classes are already not prescribed for pregnant women—but in at least some of these miscarriage cases, it's likely that women took the antibiotics not realizing that they're pregnant. 

"Infections are prevalent during pregnancy," study author Dr. Anick Bérard, PhD, said in a release for the news.  "Although antibiotic use to treat infections has been linked to a decreased risk of prematurity and low birth weight in other studies, our investigation shows that certain types of antibiotics are increasing the risk of spontaneous abortion, with a 60% to two-fold increased risk...Given that the baseline risk of spontaneous abortion can go as high as 30%, this is significant. Nevertheless, the increased risk was not seen for all antibiotics, which is reassuring for users, prescribers and policy-makers."

This study was based on association and doesn't necessarily prove cause-and-effect. Still, if there's a chance you could be pregnant, let your doctor know, so you can err side of caution and take an antibiotic class that doesn't carry this risk.