Major central nervous system malformations notified in Northern Ireland, 1969 to 1973.

In Northern Ireland, during the years 1969 to 1973, there were 485 notifications of anencephalus, 525 of spina bifida and 328 of hydrocephalus in a population of 157,725 (live and still) births. The data were based on the voluntary notification system for congenital malformations which has been operating in Northern Ireland and in England and Wales sine 1964. The malformation rates per 1000 (live and still) births were 3-1 for anencephalus, 3-3 for spina bifida and 2-1 for hydrocephalus. Secular trends in these data indicate a decrease in the incidence of all three major central nervous system malformations, but this is significant only in relation to anencephalus. Spina bifida was more common in female births than in male births, and 79 per cent of affected infants were liveborn. Indirect evidence suggests that some 40 per cent of the total number of live and stillborn infants having spina bifida at birth will survive to one year of age.