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Antibiotics in pregnancy could increase miscarriage risk

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Some common antibiotics used during early pregnancy could double the risk of miscarriage, according to a new study by the University of Montreal in Canada, published in the Canadian Medical Association Journal.

The researchers found a link between the use of macrolides, quinolones, tetracyclines, and some other common antibiotics in early pregnancy and an increased risk of miscarriage.

Miscarriage is defined as the spontaneous loss of a fetus before 20 weeks of pregnancy.

Over half of all miscarriages are caused by abnormalities in the chromosomes of the fetus. Other important factors that may raise the risk of miscarriage include diabetes, polycystic ovary syndrome, obesity and infection.

Antibiotics are widely used during pregnancy to help treat infection, but studies assessing their safety have produced conflicting results, the researchers stressed. “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,” they explained.

Data from the 1998-2009 Quebec Pregnancy Cohort was reviewed. It included 8,702 women aged between 15 and 45 years who had experienced a miscarriage at a mean gestational age of 14 weeks. These women were matched to 87,020 controls. Antibiotic exposure in early pregnancy was identified among 1,428 (16.4 percent) women who had a miscarriage and 11,018 (12.6 percent) controls.

The researchers found that the use macrolides (excluding erythromycin), quinolones, tetracyclines, sulfonamides, and metronidazole were associated with increased risk of miscarriage in early pregnancy.

The increased risk ranged from 65% to a more than twofold increase. Nitrofurantoin – an antibiotic commonly used to prevent and treat urinary tract infections – was not linked to a greater miscarriage risk. Use of the quinolone antibiotic norfloxacin was associated with a nearly fivefold increase in risk.

However, we have to point out that the infection severity may have contributed to the miscarriages identified and not the effect of the antibiotics only, which is a serious limitation of the reliability of the study.

The researchers believe that their findings question the safety of antibiotic use in early pregnancy and that the guidelines for the treatment of infections during pregnancy could be revised.



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