Screening for congenital neural tube defects in a high-risk area: an epidemiological perspective.

Data from the Glasgow Register of Congenital Malformations were used to investigate the extent of the recent decline in the prevalence of anencephaly and spina bifida, and the contribution of antenatal screening to it. Over the period 1974-85 inclusive, 303 pregnancies with an anencephalic foetus were diagnosed, representing an "adjusted" prevalence of 1.9 per 1000 total births, of which 179 (59%) were terminated following antenatal screening. There were 364 pregnancies with a spina bifida foetus representing an "adjusted" prevalence of 2.3 per 1000 total births, of which 84 (23%) were terminated. Over the study period, the "adjusted" prevalence of anencephaly fell by 50% while the birth prevalence fell by 89%; the "adjusted" prevalence of spina bifida fell by 38% while the birth prevalence fell by 76%. It was concluded that although the birth prevalence of both defects (particularly anencephaly) would have declined substantially in the absence of screening, the West of Scotland programme should continue.