A cleft is a birth defect that occurs when the tissues of the lip and/or palate of a fetus do not properly fuse very early in the pregnancy. A cleft lip, sometimes referred to as a harelip, is an elongated opening between the upper lip and the nose. It may involve one or both sides of the lip and may occur with or without a cleft palate. A cleft palate, in which the roof of the mouth abnormally opens into the floor of the nose, may also occur without a cleft lip.

One of every 30 babies is born with some type of birth defect. Approximately one in 700 has a cleft, the fourth most common birth defect in the United States (congenital heart defect is the most prevalent). Twice as many boys as girls are afflicted with a cleft lip, both with...