Little is known about the safety of most medications when used by pregnant women. Macrolides, a class of antibiotics that includes erythromycin, are the second most commonly prescribed antibiotics during pregnancy. They are especially important for treating chlamydia because other effective treatments for this disease are not recommended for pregnant women.
Some studies have suggested that taking macrolides during pregnancy could increase the risk to the fetus of a congenital heart defect—a problem with the heart’s structure that can obstruct normal blood flow—or pyloric stenosis, a condition that can prevent food from moving from the stomach to the small intestine. Other studies have found no such associations.
To learn more, researchers supported through the Developmental Biology and Structural Variation Branch studied 4,132 infants with congenital heart defects, 735 with pyloric stenosis, and 6,952 healthy infants.
The researchers found no associations between taking macrolides during pregnancy and congenital heart defects, pyloric stenosis, or other major congenital malformations, although they did find a possible association between macrolide use and genital system defects (PMID: 23254249).