Azithromycin crosses the placenta. Considered compatible in pregnancy. Limited data have suggested that using macrolides in the first trimester might be associated with a small increased chance of heart defects, but the majority of studies have not found an increased chance of heart defects or other birth defects. Some reports suggest that using macrolides during pregnancy might be associated with an increased chance of pyloric stenosis. Other studies have not supported this finding.
Because of the low levels of azithromycin in breastmilk and use in infants in higher doses, it would not be expected to cause adverse effects in breastfed infants. Unconfirmed epidemiologic evidence indicates that the risk of infantile hypertrophic pyloric stenosis might be increased by maternal use of macrolide antibiotics during the first two weeks of breastfeeding, but this has not been confirmed and data is conflicting. Monitor the infant for gastrointestinal intolerance.