5 Commonly Used Antibiotics Linked To Higher Miscarriage Risk


A new study links the use of certain classes of antibiotics to an raised risk of miscarriage in early pregnancy. Not associated with increased miscarriage risk was erythromycin and nitrofurantoin, often used to treat urinary tract infections in pregnant women.

Dr. Anick Bérard, Faculty of Pharmacy, Université de Montréal, said:

“Infections are prevalent during pregnancy. 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."

The 5 classes of antibiotics showing higher risk were:

  • macrolides

  • quinolones

  • tetracyclines

  • sulfonamides

  • metronidazole

In this case–control study, Bérard and colleagues investigated data from the Quebec Pregnancy Cohort between 1998 and 2009. 8,702 cases, defined as clinically detected spontaneous abortions, were matched with 87,020 controls; mean gestational age at the time of miscarriage was 14 weeks of pregnancy.

A total of 1,428 (16.4%) cases were exposed to antibiotics during early pregnancy compared to 11,018 (12.6%) in controls. The paper’s authors anticipate the findings may be useful for policy-makers to update guidelines for the treatment of infections during pregnancy.

Strengths And Weaknesses

Participants were between the ages of 15 and 45 years and covered under Quebec’s drug insurance plan. Women who miscarried were more likely to be older, living alone and to have multiple health issues and infections, all of which were taken into account in the analyses.

“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.

Study strong points include having a large sample, the valid information on filled prescriptions and routinely collected information on diagnosis of spontaneous abortion or related procedures.

The authors do note that infection severity could have contributed to pregnancy loss and explain some of the increased risk, although they did adjust for this variable in the analysis.

Flory T. Muanda, Odile Sheehy, and Anick Bérard
Use of antibiotics during pregnancy and risk of spontaneous abortion
CMAJ May 1, 2017 189:E625-E633; doi:10.1503/cmaj.161020

Last Updated on November 1, 2022