Secular trends in the incidence of anencephalus and spina bifida in Belfast and Dublin 1953-1973.

ASTUDY was made of the incidence of anencephalus and spina bifida in Belfast and Dublin 1953-73. The frequency of anencephalus averaged 4.1 per 1,000 (live and still) births and 4.2 per 1,000 deliveries in Belfast and Dublin respectively. In spina bifida the Belfast rate 1964-73 was 4.0 and for Dublin 1961-62 the rate was 3.5. Over the 21 years examined the incidence of anencephalus in Dublin has slowly declined but this fall was not experienced in Belfast. Spina bifida in Belfast, however, has decreased in frequency since 1964; also fewer cases numerically are being delivered due to these secular trends combined with the recent decline in the birth rate.Some aspects of these findings and their implications for secondary prevention of spina bifida in the community are discussed.