About 120,000 babies in the U.S. are born each year with a birth defect. The most common include heart defects, cleft lip and cleft palate, Down syndrome and spina bifida.

Many birth defects develop early during pregnancy, sometimes before a woman even knows she is pregnant, according to the Centers for Disease Control and Prevention. However, there are precautions expectant mothers can take to increase the chances of having healthy babies.