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Common Drugs That Treat UTIs Linked to Increased Risk for Miscarriages

A new study found that use of certain antibiotics, including those commonly used to treat vaginal or urinary tract infections, during early pregnancy was associated with an increased risk of spontaneous abortion.
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As if the idea of growing a tiny human inside your body isn't daunting enough, a new study released today from the Canadian Medical Association Journal found that some common antibiotics actually increase the risk of having a miscarriage.

Researchers from the Université de Montréal in Canada analyzed data from the Quebec Pregnancy Cohort, a collection of data on all pregnancies of women covered by the Quebec Public Prescription Drug Insurance Plan, from 1998 to 2009. The cases in the study, totaling more than 95,000, featured women who were between the ages of 15 and 45; of the sample, 8,702 pregnancies were determined to have ended in miscarriage before the 20th week of gestation.


Researchers considered antibiotic exposure as having at least one prescription during the gestation period, and they focused on several common classes: cephalosporins, macrolides, penicillins, quinolones, sulfonamides, tetracyclines, other antibacterials, antiprotozoals and urinary anti-infectives.

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A total of 1,428 cases (16 percent) were exposed to antibiotics in early pregnancy. A large number of those women (560) were prescribed penicillin and cephalosporins, both of which have a long history of research proving its safety. Additionally, researchers noted that "women with spontaneous abortion were more likely to be older, to be living alone, and to have comorbidities and infections," the study states.

After adjusting for a number of factors, the study found that the "use of macrolides (excluding erythromycin), quinolones, tetracyclines, sulfonamides and metronidazole during early pregnancy was associated with an increased risk of spontaneous abortion," the study states. In the cases of azithromycin and clarithromycin (both macrolides), the risk of spontaneous abortion increased by 65 percent and twofold, respectively, which was consistent with findings in previous studies.

According to the US National Library of Medicine, azithromycin and clarithromycin are both used to treat certain bacterial infections, such as bronchitis, as well as infections in the ears, throat and sinuses. Metronidazole, in its topical form, is commonly used for adult acne and some vaginal infections, while sulfamethoxazole and trimethoprim, two medications in the sulfonamide family, are used for urinary tract infections.


The study states that doctors already have obstetric guidelines to avoid prescribing tetracyclines and quinolones during early pregnancy. According to the UK Teratology Information Service, tetracycline, which is often used to treat acne, is known to discolor an unborn baby's milk teeth when taken in the second and third trimester and could possibly impact bone growth. Quinolones, used to treat a range of infections including in the respiratory tract and gastro-intestinal system, have been shown to cause arthropathy in animal studies.

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Anick Bérard is a professor at the Faculty of Pharmacy at the Université de Montréal and lead author on the study. She says despite how alarming these results appear, the risk of a miscarriage remains small. "The risk of clinically detected miscarriages has a baseline risk of approximately 6-7 percent," she explains. "Hence a 60 percent increased risk would mean going from a 6-7 percent baseline risk (with no antibiotics exposure) to 9-10 percent (among those using antibiotics)."

What is even more reassuring, Bérard points out, is that "we found that penicillin, cephalosporin, erythromycin—the most frequently used antibiotics—are not associated with an increased risk of miscarriage. We also found that nitrofurantoin, mostly used to treat urinary tract infections, are actually decreasing the risk of miscarriage. This needs to be replicated given that we are the first team to show that."

"The take home message is that infections need to be treated during pregnancy," Bérard says. "Women should seek medical counsel to identify the best treatment option."