Front and sides of the face and palatine shelves imperfectly fused during pregnancy

Twice as common in males as in females

More common in children with a family history of cleft defects

Cleft lip with or without cleft palate: occurs in about 1 in 1,000 births among Whites; higher incidence in Asians (1.7 in 1,000) and Native Americans (more than 3.6 in 1,000), but lower in Blacks (1 in 2,500)

May occur separately or in combination

Occurs unilaterally, bilaterally or, rarely, in the midline

May affect just the lip or extend into the upper jaw or nasal cavity (see Types of cleft deformities, pages 58 and 59)

Increases susceptibility to middle ear infections and potential hearing loss

Chromosomal abnormality, exposure to teratogens, genetic abnormality, or environmental factors cause the lip or palate to fuse imperfectly during the second month of pregnancy.

Complete cleft includes the soft palate, bones of the maxilla, and alveolus on one or both sides of the premaxilla.

Double cleft runs from the soft palate to either side of the nose, separating the maxilla and premaxilla into freely moving segments; the tongue and other muscles may displace the segments, thus enlarging the cleft.

Chromosomal or Mendelian syndrome (cleft defects caused by more than 300 syndromes)