Taking certain antibiotics early in pregnancy may increase the risk for birth defects, a new study reports.
British researchers studied more than 180,000 children whose mothers were prescribed either penicillin or one of the macrolide antibiotics — such as erythromycin, clarithromycin or azithromycin — during or up to a year before pregnancy. Macrolides are often prescribed for people allergic to penicillin.
The scientists found that compared with mothers who took penicillin in the first trimester, those who took macrolides had a 55 percent increased relative risk of having a baby with a major birth defect involving the nervous, cardiovascular, gastrointestinal, genital or urinary system. The risk was especially high for cardiovascular malformations.
The study controlled for many factors known to increase the risk for birth defects, including the use of alcohol or illicit drugs, smoking, hypertension and diabetes. The report is in BMJ.
The risk did not increase for women prescribed macrolides before becoming pregnant, or for those who took them later in pregnancy. Antibiotics were not associated with an increased risk for cerebral palsy, attention deficit hyperactivity disorder or autism.
The lead author, Heng Fan, a researcher at University College London, said that this very large observational study was needed to detect a modest effect, and that pregnant women with bacterial infections should not refuse antibiotics, since bacterial infections can be far more damaging to the unborn baby.
“But,” she added, “our findings suggest that it’s better to avoid macrolides if other antibiotics can be used.”