Why does cleft lip and palate occur?

In most cases of cleft lip and palate, the cause is never known. One in every 625 babies born in Ireland has a cleft of the lip and/or palate. It is thought to occur as a combination of genetic and environmental factors, since having a sibling or parent with a cleft increases the chance of clefting in a newborn. Despite this, most cases occur in families without any history of clefting and it is important to realise that it is highly unlikely to be the result of any action on your part.

There is some evidence that certain medications during pregnancy (certain anti-epilepsy drugs, acne drugs and chemotherapy drugs) increase the chance of a cleft occurring.
Sometimes, clefting is present as part of a number of syndromes, where additional conditions affect the newborn baby.

Whilst it is not known why clefts occur, they are generally a failure of complete fusion of the various prominences that come together to form the face.