Weighing the risks of antibiotics in early pregnancy

Study looked at women with miscarriages and antibiotics they took for sickness.

To better understand whether antibiotics might present risk, researchers at the University of Montreal published a new study looking at a group of women who had miscarriages and the different types of antibiotics they were prescribed for sickness during their pregnancies.

Antibiotics are an essential mainstay in treating pregnant women, who are often vulnerable to infections due to weakened immune systems. Left untreated, bacterial infections can lead to complications that threaten both the life of the mother and the child.

Researchers found that some common antibiotics increased the risk of a woman miscarrying, however the overall risk was extremely low.

"Taking one of those drugs, the increase in the risk of spontaneous abortion, it’s incremental," Bérard told ABC News. "It’s a rare event to begin with, so no one should panic."

Bérard, along with her co-authors at the University of Montreal, found that certain classes of antibiotics -- macrolides, tetracyclines, fluoroquinolones, sulfonamides and metronidazole -— were associated with an increased likelihood of clinically-detected miscarriage before 20 weeks of pregnancy.

Antibiotics routinely used to treat infections ranging from respiratory illnesses to urinary tract infections —- such as Z-Paks (azithromycin, a macrolide), Flagyl (metronidazole), Bactrim (sulfamethoxazole / trimethoprim, sulfonamides) — were all associated with an increased risk for miscarriage.

Only erythromycin, a type of macrolide often used to treat bronchitis, and nitrofurantoin, a type of antibiotic often used to treat urinary tract infections, were not associated with miscarriage.

"Infections should be treated during pregnancy, but it's a question of what we’re treating with," Bérard said. "We have to remember that antibiotics are taken for short period of time, for five to ten, max 15 days."

She said the study can help doctors make informed decisions if they are treating common infections during pregnancy such as urinary tract infections (UTIs).

"The question is, how should they be treated? Our study found that penicillins and cephalosporins are not associated with risk of spontaneous abortion," Bérard said. "Similarly, we found no risk with erythromycin and nitrofurantoin, these are some of the most-used drugs used to treat UTIs, so our study shows that they are real treatment options."

The methods used in the study could have affected the findings, according to Heine, which are a limitation. For example, the doctors may not have been aware of the pregnancies before they prescribed the medication. Additionally, some of the miscarriages may have been misdiagnosed as infections.

The study joins a growing body of studies that have offered conflicting information about the risks of taking certain antibiotics during pregnancy.

"Pregnant women are not included in randomized control trials before a drug becomes available in market," Bérard said. "But, infections are very prevalent during pregnancy, and antibiotics will be prescribed. Studies like ours give treatment options."