Antibiotics Commonly Prescribed To Pregnant Women Linked To Birth Defects

A class of antibiotics commonly prescribed to pregnant women is associated with an increased risk of major birth deformities, particularly heart defects, when compared with penicillin, according to a study published in BMJ.

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Macrolides are a type of antibiotic derived from soil-born bacteria and used to treat common bacterial infections such as strep throat, particularly as an alternative for those with penicillin allergies. Known more commonly under the generic names of azithromycin, erythromycin, and clarithromycin, macrolides should be used with caution during pregnancy and only if alternatives are not available.

To assess the association between macrolides and major malformations of the heart and genitals, as well as four neurodevelopment disorders, researchers at University College London looked at data from more than 100,000 children born in the UK between 1990 and 2016 via the UK Clinical Practice Research Datalink, a national database that covers around 7 percent of the UK population. They also analyzed another 82,314 children whose mothers were prescribed one macrolide or penicillin before pregnancy and more than 53,000 of their siblings. Almost one-third of mothers in the population were prescribed at least one antibiotic during pregnancy; penicillin and macrolides accounted for about 69 and 10 percent of all prescriptions, respectively.

When accounting for other influencing factors, researchers found that macrolides in the first trimester of pregnancy were associated with an increased risk of major malformations compared with penicillin, specifically those of the cardiovascular system. Children were also slightly more likely to be at risk of genital malformations. In all, about 2.1 percent of children born to more than 8,600 mothers prescribed macrolides were born with a major defect compared with 1.7 percent of children whose mothers were given penicillin. Researchers did not reveal a link to macrolide use and neurodevelopment disorders like cerebral palsy, epilepsy, ADHD, and autism spectrum disorder.

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"Macrolide antibiotics are used to treat a wide variety of bacterial infections, and are among the most frequently prescribed antibiotics during pregnancy in Western countries,” said lead author, PhD candidate Heng Fan in a statement.

"This work builds on previous evidence of rare but serious adverse outcomes of macrolide use, especially for unborn babies. These adverse outcomes were assumed to be associated with the arrhythmic effect of macrolides and policy advice about their use in pregnancy varies."

Because it is an observational study, the researchers are quick to caution that a cause cannot be determined by their work. If future studies determine a causal link, Fan adds that an estimated four in every 1,000 children born to mothers prescribed macrolides in the first trimester would be born with cardiovascular malformations.

"Our findings suggest it would be better to avoid macrolides during pregnancy if alternative antibiotics can be used,” said Professor Ruth Gilbert of UCL Great Ormond Street Institute of Child Health. "Women should not stop taking antibiotics when needed, as untreated infections are a greater risk to the unborn baby."

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