Macrolides taken in pregnancy have been linked to an increased risk of cardiac and genital malformations in offspring in a large population-based study.

The findings have led to calls for prescribing caution and a review of GP prescribing guidelines, although the absolute risk of the anomalies occurring is small.

The study found that prescription of macrolides in the first trimester was associated with an increased risk of any major malformation compared with penicillin (27.7 v 17.7 per 1000) but particularly cardiovascular anomalies, with a 60% increased relative risk.

In addition, taking macrolides at any time during pregnancy was linked with increased risk of genital tract malformation, mainly hypospadias.