The use of certain antibiotics during early pregnancy may increase the risk of spontaneous abortion, according to a new study published in the Canadian Medical Association Journal (CMAJ).

Antibiotics are commonly used among pregnant women but data regarding fetal safety “remains limited.” Flory T. Muanda, MD, and colleagues from Université de Montréal, Montréal, Quebec, searched the Quebec Pregnancy Cohort (1998–2009) database, excluding planned abortions and pregnancies with exposure to fetotoxic medications. Women aged 15–45 years on the first day of gestation who were insured for at least 12 months pre- and post-pregnancy were included. Study authors selected 10 controls per case and matched them based on gestational age (within 3 days) and year of pregnancy. 

Antibiotic use was defined as filled prescriptions between the first day of gestation and the index date and was compared with non-exposure vs. exposure to penicillins or cephalosporins.  

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The study data showed that the use of azithromycin (adjusted odds ratio [OR] 1.65, 95% CI: 1.34–2.02), clarithromycin (adjusted OR 2.35, 95% CI: 1.90–2.91), metronidazole (adjusted OR 1.70, 95% CI: 1.27–2.26), sulfonamides (adjusted OR 2.01, 95% CI: 1.36–2.97), tetracyclines (adjusted OR 2.59, 95% CI: 1.97–3.41), and quinolones (adjusted OR 2.72, 95% CI: 2.27–3.27) was associated with a higher risk of spontaneous abortion. Study authors observed similar results when penicillins or cephalosporins were used as the comparator group.

In general, an increased risk of spontaneous abortion was seen with the use of macrolides (except erythromycin), quinolones, tetracyclines, sulfonamides, and metronidazole during early pregnancy. “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,” states Dr. Bérard. 

The authors note that infection severity could be a confounder, although they did adjust for this variable in the analysis. Findings from the study may be useful for policymakers in updating treatment guidelines for infections during pregnancy. 

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