In simple terms, a cleft is a split or gap in a structure. A split upper lip is called a “cleft lip”, while the term “cleft palate” refers to a gap in the roof of the mouth.
A cleft may occur on one or both sides, with varying degrees of severity. In its mildest form there is only a slight notch of the upper lip. The most severe form includes a cleft of the lip that extends up into the nose, through the bony ridge from which the teeth erupt and into the palate. This is known as a “complete cleft lip and palate”.
When an unborn baby grows, the lip and the palate develop separately, so it is possible for a child to have only a cleft lip, only a cleft palate, or both. When the defect only involves one side of the lip, it is called a unilateral cleft lip. A bilateral cleft lip involves both sides.
A cleft palate does not mean that the palate is “missing” although it sometimes may look that way. Rather, the two sides of the palate did not join together (fuse) as they should in the early weeks of embryonic development. Cleft palates can vary in extent. They may involve just the back of the soft palate or extend to the hard palate just behind the gums.