Taking these commonly prescribed antibiotics while pregnant may increase the risk of miscarriage, Canadian study says

Several commonly prescribed antibiotics are associated with a higher risk of miscarriage in early pregnancy, a new study published Monday in the Canadian Medical Association Journal (CMAJ) has found.

However, while antibiotics like macrolides, quinolones, tetracyclines, sulfonamides and metronidazole were among those linked to a 60 per cent to two-fold increased risk of miscarriages, others like erythromycin and nitrofurantoin were not.

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“We’re not the first study to look into this, but this is a bigger study with a larger sample group, and our results were pretty concordant with what existing research has found,” says Dr. Anick Bérard, of the faculty of pharmacy at the Université de Montréal and author of the study. “But I think the highlight is not so much that some antibiotics are increasing the risk of miscarriage, but that some of the most used antibiotics are not linked to miscarriage.”

The team looked at data from the Quebec Pregnancy Cohort between 1998 and 2009 which included participants between the ages of 15 and 45. For this study, 8,702 cases that were classified as detected spontaneous abortions were matched with 87,020 controls (which means gestational age at the time of miscarriage was 14 weeks of pregnancy).

Of those, just over 16 per cent of cases were exposed to antibiotics during early pregnancy – that’s compared to almost 13 per cent in controls.

The study also found that women who miscarried were more likely to be older, living alone, and to have multiple health issues and infections. This was taken into account when the research team looked over the data.

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Bérard explains that women in early pregnancy are susceptible to infections – more specifically, urinary tract infections, which are treated by antibiotics.

But current guidelines recommend that physicians don’t prescribe antibiotics to women who are pregnant. With these findings, however, Bérard says that may change.

“The take-home message is that infections should be treated,” Bérard says. “It’s not a question of treating versus not treating. Infections themselves have been associated with an increased risk of prematurity and low birth weight.”

Bérard adds, “The bottom line is to treat infections, but our study has shown that some the most used antibiotics like erythromicine and nitrofurantoin are not associated with miscarriage. So, yes treat the infection, and we are giving treatment options.”

The research team hopes that this new information will be useful for policy-makers to update guidelines when it comes to treating infections during pregnancy.

However, a previous study by Columbia University’s Mailman School of Public Health found in 2014, that taking antibiotics during the second or third trimester of pregnancy increases the risk for childhood obesity.