FETAL EXPOSURE TO ANTIBIOTICS. “Early in utero exposures can lead to altered organogenesis and fetal development. Antibiotics, including penicillins, nitrofurans, and cephalosporins, are commonly prescribed for a wide range of ailments during the periconceptional and prenatal periods.”
http://www.nature.com/ijo/journal/v37/n7/full/ijo201347a.html