Antibiotic use during early pregnancy, including some macrolides, quinolones, tetracyclines, sulfonamides, and metronidazole, is associated with an increased risk of spontaneous abortion, according to a study published in Canadian Medical Association Journal.

Flory T. Muanda, MD, from the Faculty of Pharmacy at the University of Montreal, and colleagues conducted a nested case–control study within the Quebec Pregnancy Cohort (1998–2009) to analyze the association between antibiotic exposure during pregnancy and risk of spontaneous abortion. Spontaneous abortion was defined as having a diagnosis or procedure related to spontaneous abortion before the 20th week of pregnancy. Use of antibiotics was defined by filled prescriptions between the first day of gestation and the date of spontaneous abortion and was compared with both non-exposure and exposure to penicillins or cephalosporins.

Women included were 15 to 45 years of age on the first day of gestation and were continuously insured by the province’s drug plan for at least 12 months before and during their pregnancy. Women who were exposed to teratogenic drugs during pregnancy or had planned abortions were excluded. Ten controls per case were randomly selected and matched by gestational age (within 3 days) and year of pregnancy.

Continue Reading

The following classes of antibiotics were considered, defined according to the American Hospital Formulary Service (AHFS) categories: cephalosporins, macrolides, penicillins, quinolones, sulfonamides, tetracyclines, other antibacterials, antiprotozoals, and urinary anti-infectives.

A total of 182,369 pregnancies met the inclusion criteria, 8702 (4.7%) of which ended with a clinically detected spontaneous abortion. The mean gestational age was 14.1 weeks. For 1068 (12.3%) of the cases, the gestational age was based on ultrasound.

After adjustment for potential confounders, use of azithromycin (odds ratio [OR] 1.65; 110 exposed cases), clarithromycin (OR 2.35; 111 exposed cases), metronidazole (OR 1.70; 53 exposed cases), sulfonamides (OR 2.01; 30 exposed cases), tetracyclines (OR 2.59; 67 exposed cases), and quinolones (OR 2.72; 160 exposed cases) was associated with an increased risk of spontaneous abortion.

An increased risk of spontaneous abortion was not associated with use of nitrofurantoin (OR 0.70; 39 exposed cases) or erythromycin (OR 0.70; 29 exposed cases).

“This finding supports current guidelines used in obstetrics that do not recommend use of these drugs in early pregnancy,” the authors said. “In contrast, previous studies failed to show an association.”


  1. Muanda FT, Sheehy O, Bérard A, et al. Use of antibiotics during pregnancy and risk of spontaneous abortion. CMAJ. 1 May 2017. doi: 10.1503/cmaj.161020