The incidence of oral clefts: a review.

We have reviewed epidemiological studies on the incidence of oral clefts in several regions of the world, but mainly in Europe. The incidence ranges from 1.0/1000 to 2.21/1000. The highest incidence was in Czechoslovakia (1.81/1000), followed by France (1.75/1000), Finland (1.74/1000), Denmark (1.69/1000), Belgium and the Netherlands (1.47/1000), Italy (1.33/1000), California (1.12/1000) and South America (1.0/1000). The data from Denmark and Finland appeared to be the most reliable. All studies showed a higher incidence of cleft lip and/or palate (CL(P)) compared with cleft palate (CP). There was a predominance of girls in the CP group, while the CL(P) group comprised mainly boys. The left side was affected twice as often as the right side. Black children had a lower incidence than white children. An attempt was made in several reports to clarify the cause of oral clefts, but opinions are contradictory.