Cleft lip is a facial and oral malformation that occurs very early in pregnancy, while the baby is developing inside the mother. Cleft lip is a physical split or separation of the two sides of the upper lip and appears as a narrow opening or gap in the skin of the upper lip. This separation often extends beyond the base of the nose and includes the bones of the upper jaw and/or upper gum. Cleft lip affects one in 700 babies annual, and is the fourth most common birth defect in the US. In most cases, the cause of cleft lip is unknown and conditions cannot be prevented. Most scientists believe clefts are due to a combination of genetic and environmental factors. There appears to be a greater chance of clefting in a newborn if a sibling, parents or relative has had the problem.