Most of these craniofacial clefts are even rarer and are frequently described as Tessier clefts using the numerical locator devised by Tessier. Classification
Cleft lip and cleft palate is an "umbrella term" for a collection of orofacial clefts. It includes clefting of the upper lip, the maxillary alveolus (dental arch), and the hard or soft palate, in various combinations. Proposed anatomic combinations include:
cleft lip
cleft lip and alveolus
cleft lip, alveolus, and palate
cleft lip and palate (with an intact alveolus)
cleft palate

Prenatal diagnosis
Cleft lip with or without palate is classified as the most common congenital birth defect. It has been noted that the prevalence of orofacial clefts varies by race. The highest number of cases have been recorded among Asians and Native Americans, followed by Europeans, Hispanics and African-Americans. The critical period for cleft development ranges from the 4th to the 12th week of intrauterine life. Clefts of the primary palate develop between the 4th and 7th weeks of intrauterine life, while clefts of the secondary palate develop between the 8th and 12th embryonic weeks. Accurate evaluation of craniofacial malformations is usually possible with the ultrasound scan performed during pregnancy. This is however not a routine procedure according to the American Institute of Ultrasound in Medicine. The accuracy of ultrasonography for prenatal diagnosis of cleft lip +/- palate is dependent on the experience of the sonologist, maternal body type, foetal position, the amount of amniotic fluid and the type of cleft. Prenatal diagnosis enables appropriate and timely education and discussion with parents by the cleft team.
Genetic factors cause clefts in 20% to 50% of the cases and the remaining clefts are attributable to either environmental factors (such as teratogens) or gene-environment interactions. The polygenic/multifactorial inheritance model predicts that most individuals will be born without clefts; however with a number of genetic or environmental factors, it can result in cleft formation.The development of the face is coordinated by complex morphogenetic events and rapid proliferative expansion, and is thus highly susceptible to environmental and genetic factors, rationalising the high incidence of facial malformations. During the first six to eight weeks of pregnancy, the shape of the embryos head is formed. Five primitive tissue lobes grow:

If these tissues fail to meet, a gap appears where the tissues should have joined (fused). This may happen in any single joining site, or simultaneously in several or all of them. The resulting birth defect reflects the locations and severity of individual fusion failures (e.g., from a small lip or palate fissure up to a completely malformed face). The upper lip is formed earlier than the palate, from the first three lobes named a to c above. Formation of the palate is the last step in joining the five embryonic facial lobes, and involves the back portions of the lobes b and c. These back portions are called palatal shelves, which grow towards each other until they fuse in the middle. This process is very vulnerable to multiple toxic substances, environmental pollutants, and nutritional imbalance.