Part two: Can taking antibiotics during pregnancy increase risk of miscarriage?

In last week’s post, I explained how miscarriage is the most common complication of pregnancy and how it can happen for a variety of reasons. In addition to those common causes, however, there may be other factors that also increase the risk of miscarriage.

A recent study found one of those factors might be taking certain antibiotics during the first half of pregnancy.

In general, we think of antibiotics as being relatively safe to prescribe during pregnancy. This new research suggests that there may be greater risk to the pregnancy than previously thought, depending on the type of antibiotic.

Studying antibiotics and miscarriage risk

The study was conducted in Canada using the Quebec Pregnancy Cohort, which collected data on all pregnancies of women covered by the Quebec Public Prescription Drug Insurance Plan for 11 years. It specifically examined the risk of miscarriage prior to 20 weeks and its association with antibiotic prescriptions. The study included more than 95,000 patients, which is one of its strengths.

Researchers compared the data of women who were prescribed antibiotics to those who were not exposed to the medications. They also knew what type of antibiotic a woman was prescribed. About 9,000 women in the study miscarried before 20 weeks of gestation; investigators evaluated if being prescribed an antibiotic was associated with an increased risk of miscarriage and if the type of antibiotic made a difference.

After controlling for factors that might impact the results – such as hospitalizations with a diagnosis of infection or prior exposure to antibiotics – the study found about 16 percent of patients who had miscarriages had also been prescribed antibiotics. Significantly fewer women, only 12.6 percent, who were not prescribed antibiotics miscarried.

Different antibiotics, different risks

The study’s results do suggest certain types of antibiotics are associated with a higher risk of miscarriage.

One of the most common antibiotics in the U.S. market is azithromycin, commonly referred to as a Z-Pak®. When azithromycin was prescribed during pregnancy, researchers saw a 65 percent increase in the risk of miscarriage. Other types of antibiotics, such as tetracyclines and quinolones, had a two- or three-fold increase in the risk of spontaneous miscarriage.

Not all antibiotics showed an increased risk, however. Cephalosporins and penicillins did not show increased risk of pregnancy loss, confirming their long history of safe utilization in pregnancy.

Recommendations

This information does not suggest you should avoid antibiotics during early pregnancy. Studies like these aren’t perfect – for example, the researchers looked at women who were prescribed antibiotics, but have no way to know that the women actually took the medication. And treating some infections is extremely important, because infections too can lead to increased risk of miscarriage.

What do I recommend? First, have an open discussion with your doctor about the need to treat all symptoms. Many sore throats and respiratory illnesses are viral and symptomatic relief is all that is necessary. Second, if you do need antibiotics, then careful selection of the right drug is important. And finally, there may be times when an antibiotic that this study suggests is associated with a higher risk for miscarriage is indicated and appropriate because of the type of infection. You should be reassured that while increased, the overall risk for miscarriage is still low.

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