Cleft lip and cleft palate are birth defects that occur when a baby's lip or mouth do not form properly. They happen early during pregnancy. A baby can have a cleft lip, a cleft palate, or both. A cleft lip happens if the tissue that makes up the lip does not join completely before birth. This causes an opening in the upper lip. The opening can be a small slit or a large opening that goes through the lip into the nose. It can be on one or both sides of the lip or, rarely, in the middle of the lip.