The incidence of cleft lip and palate in Northern Ireland from 1980-1990.

This study reports the incidence of the various types of cleft lip and/or palate drawn from a regional database of all affected children born in Northern Ireland during the period 1980-1990. The incidence of these anomalies was 1.28 per 1000 live births (1:781). Fifty-three per cent of clefts involved the secondary palate only, 16 per cent the primary palate only, 26 per cent involved both primary and secondary palate, and 5 per cent were unconnected. Overall, more males than females were affected and there were more males than females in the group having complete clefts. Separate clefts of lip and palate occurred exclusively in males with only one exception. Unilateral clefts were more common on the left side. Within the group showing complete unilateral cleft of the primary and secondary palate, left-sided clefts were more commonly male, right-sided clefts were more commonly female. There were no statistically significant sex differences between sides in the unilateral primary palate cleft group.