Physical defect in the development of the upper part of the mouth, including the lip and palate, or roof of the mouth.

Over 5,000 babies are born each year in the United States with a cleft lip or palate (about 1 in every 700 births). Cleft lip without cleft palate is the third most common congenital malformation among babies born in the United States, and is estimated to occur roughly twice as often in males than in females. Cleft palate without cleft lip is the fifth most common, and it affects roughly twice as many girls as boys. Clefts may be unilateral (affecting the left or right side only) or bilateral (affecting both sides). Left-side clefts represent 70% of all unilateral clefts. Research in the 1980s and 1990s indicated that the incidence of lip and palate clefts was increasing. In the United States, Native Americans have...