Given recent news reports that some penicillin-alternative antibiotics (in a group called ‘macrolides’, which includes erythromycin, clarithromycin, or azithromycin) given during pregnancy may lead to malformations in the baby, we want to reassure you that there are no implications in relation to antibiotics used in labour to protect against group B Strep infection in newborn babies.
The first-line antibiotic that is used for women in labour against early-onset GBS infection is Penicillin G (also known as Benzyl Penicillin), given intravenously as soon as possible once labour has started, and at 4-hourly intervals until the baby is born. There is no suggestion that Penicillin G given in labour causes any malformations in the baby.
If a woman is allergic to penicillin and has one or more recognised risk factors for her baby developing early-onset GBS infection, she will be offered an alternative antibiotic to be given intravenously during labour. This alternative is usually a cephalosporin, such as Cefuroxime, or in cases of severe allergy Vancomycin. Neither is part of the macrolide family that recent research suggests may cause major malformations if given in the first trimester of pregnancy (up to 12 weeks’ gestation) or minor genital malformations if given later in pregnancy.
Penicillin, Cefuroxime and Vancomycin have been used in labour for many years to prevent group B Strep infection, and are not known to cause fetal malformations at any stage of pregnancy.
A recently published paper suggests that there is a small risk (1.7 per 1000) of macrolides causing minor genital malformations if they are used during the second and third trimesters to treat infections (such as in the urinary tract, or as preventative medicine for preterm prelabour rupture of membranes) (Fan et al . BMJ 2020;368:m331)