Miscarriages and antibiotics

An alarming 15 to 20 percent of confirmed pregnancies end in miscarriage. If that statistic isn't worrying enough, researchers have just learned that some common classes of antibiotic can double the risk of miscarriage.

Scientists from the University of Montreal in Canada have discovered a link between the use of tetracyclines, quinolones, macrolides and some other common antibiotics in early pregnancy and an increased risk of miscarriage.

Miscarriage as defined here is the spontaneous loss of a fetus before 20 weeks of pregnancy. Over fifty percent of all miscarriages are caused by abnormalities in the chromosomes of the fetus. Miscarriages are most common among women 35 years of age and older.

The scientists drew upon the 1998-2009 Quebec Pregnancy Cohort for their dataset. These data included 8,702 women aged between 15 and 45 years who had experienced a miscarriage at a mean gestational age of 14 weeks. The women were referenced against 87,020 controls.

Exposure to antibiotics in early pregnancy was identified among 1,428 16.4 percent of the women who had a miscarriage and 12.6 percent of the controls. The data showed how the use of certain antibiotics in early pregnancy increased the risk of miscarriage by as much as 200 percent.

"We aimed to quantify the association between exposure to antibiotics during pregnancy and the risk of spontaneous abortion, taking into account methodologic limitations of previous studies," explained study co-author Dr. Anick Bérard, of the Faculty of Pharmacy at the University of Montreal.

Antibiotics are widely used during pregnancy to help treat infection, but previous studies have yielded conflicting results regarding their value and harm.

In the Canadian study, the use of macrolides – excluding erythromycin – in early pregnancy was associated with increased miscarriage risk, as were quinolones, tetracyclines, sulfonamides, and metronidazole. Nitrofurantoin - an antibiotic commonly used to prevent and treat urinary tract infections - was not linked to a greater miscarriage risk.

The scientists acknowledge that the severity of the infections the antibiotics were prescribed to treat may have contributed to the miscarriages identified.

Still, they believe that their findings question the safety of antibiotic use in early pregnancy, concluding: "Our findings may be of use to policy-makers to update guidelines for the treatment of infections during pregnancy."

The research was published in the Canadian Medical Association Journal.