A cleft is a separation of parts of the mouth that are usually joined together during the early weeks of the development of an unborn child. Cleft lip is a separation on one or both sides of the upper lip and, quite often, of the dental ridge as well. Clefts of the palate, or roof of the mouth, may occur in the bony hard palate or in the soft palate at the back of the mouth, or both. Cleft lip may involve only one side of the upper lip or both. The split may be only in the upper lip, or may extend up into the nostril. Usually the split goes through the outer skin, muscles, and inside of the lip. Feeding is the first problem to be overcome. Since a split in the roof of the mouth makes it difficult for a baby to suck, food backs up through its nose and may cause choking. Defective speech is one of the most serious results of cleft palate and, to a lesser extent, cleft lip. Psychological problems may result from speech difficulties and the child's unusual appearance before clefts are repaired, may require a professional counsellor's help. Clefts have no relation to mental ability or retardation. Ear infections are common: difficulty in swallowing affects air pressure around the inner ear, spreading infection directly through the nose to ear; frequent or severe ear infections may lead to hearing loss.
Around 5 babies per 10,000 are born with a cleft palate and up to twice as many with a total cleft lip, although rates for cleft lip vary considerably in different countries and are up to twice the world average in Asia, Scandinavia and Canada. The defect appears more often among orientals and certain tribes of American Indians than among white Americans. It occurs less frequently among black Americans.
In the last 30 years in the USA, the number of children born with a cleft increased from one for every 1,000 live births to one for every 700. About 40% have both cleft lip and palate. The cleft recently overtook clubfoot as the top defect overall.