MAY 02, 2017 7:52 AM PDT

Early Pregnancy Antibiotic Use Tied to Miscarriage


Women may have an increased risk of a miscarriage if they’ve been exposed to some antibiotics in the early pregnancy.

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Given the extraordinary changes in a wide range of physiological processes during pregnancy, infections in mothers-to-be are not uncommon. In particular, pregnant women are most prone to getting yeast infections during their second trimester. But women who are treated with certain antibiotics may have a near two-fold increased risk of miscarriage, researchers report in the Canadian Medical Association Journal.

For the study, researchers led by Anick Bérard, combed through medical records of women in the  Quebec Pregnancy Cohort between 1998 and 2009. The women were from 15 to 45 years of age. Berard’s team identified around 8,700 cases of spontaneous abortions occurring on average at 14 weeks of pregnancy, and compared them to the over 87,000 healthy pregnancies. They found that over 16 percent of women who miscarried had taken antibiotics during the early 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,” said Berard.

However, not all antibiotics carry the same risks, and penicillin, the most commonly prescribed antibiotic, was not associated with increased miscarriage. "It is reassuring to see that first-line treatments and antibiotics that are the most used in the population (penicillin, cephalosporin) were not associated with an increased risk of miscarriage," said Berard.

The drugs with the highest risks include macrolides (excluding erythromycin), quinolones, tetracyclines, sulfonamides, and metronidazole. And of this, doctors already avoid tetracyclines and quinolones during pregnancy due to concerns over birth defects. The remaining classes of antibiotics are commonly used to treat infections of the urinary tract, ear, eye, vagina, and respiratory tract.

The findings are consistent with some previous studies linking antibiotic exposure and risk to the fetus. In addition, the results confirm existing practices of avoiding quinolones and tetracyclines for pregnant women.

Although the authors conclude an increased risk with these antibiotics, they maintain that “The risk remains small," Bérard said. A pregnant woman’s ordinary risk of miscarriage is estimated to be around 6 to 7 percent. With antibiotic exposure, the risk of miscarriage increases to 9 to 10 percent. "The take-home message is that infections need to be treated during pregnancy," said Berard, reiterating that women should consult with their doctors for the best treatment plans.  

Additional sources: CNN

About the Author
  • I am a human geneticist, passionate about telling stories to make science more engaging and approachable. Find more of my writing at the Hopkins BioMedical Odyssey blog and at
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