Some epidemiological data on oral clefts in the northern Netherlands, 1981-1988.

Cleft lip with or without cleft palate [CL(P)] has a high prevalence [corrected] in the northern Netherlands. Several epidemiological parameters for oral clefts, including both CL(P) and cleft palate (CP), were analysed and compared with the literature. Except for the high prevalence at birth of isolated CL(P) no major differences in the pattern of occurrence described elsewhere were found. So far, descriptive epidemiological studies have not given any insight into the aetiology of this high CL(P) prevalence [corrected] in the Northern Netherlands. Therefore, case control studies on possible risk factors have been initiated.