Epidemiology of cleft lip and palate. An attempt to rule out chance correlations.

The findings of a previous epidemiological study on oral clefts (599 children) were tested in an independent sample of 194 children, using the same source as for the previous study (Finnish Register of Congenital Malformations). Several of the earlier results--such as seasonal variation and associations between clefts and parental age, social factors, and emotional stress--were not reproduced. It is concluded that chance correlations introduce a marked problem to epidemiological studies. The findings of both studies show that there is an exceptionally high incidence of cleft palate in Finland. Significant geographical variations and associations between clefts and prematurity, threatened abortion during the first and second trimesters, maternal drug consumption during the first trimester, and influenza and fever during the first trimester were found. The possible role of these findings in the aetiology of oral clefts is discussed, and particular attention is paid to the possible teratogenicity of salicylates.