At one time people thought that if a pregnant woman had bad or frightening thoughts, or if she encountered gypsies or a fish with a gaping mouth, she would have a baby with a cleft. We now know these stories are not true. There is no single cause for cleft lip or cleft palate. A cleft can occur without a known reason. Sometimes factors such as disease, drugs, and alcohol can act on the developing fetus and result in a cleft.
Heredity can play a role in causing clefts.
If either parent has a cleft, the chances increase that the baby will have a cleft. If both parents are normal and have a baby with a cleft, the chances that they will have another baby with a cleft increase. Many children with clefts have other problems and defects as well. They may grow more slowly or have learning difficulties. Sometimes clefts are associated with hereditary diseases that the family may be unaware of.