East Ireland 1980-1994: epidemiology of neural tube defects

The objective of the study was to describe the epidemiology of neural tube defects (NTD) in the eastern region of Ireland using the EUROCAT register of congenital malformations.

EUROCAT registries monitor the prevalence of congenital anomalies in defined populations using multiple sources for case ascertainment. All cases of NTD on the Dublin EUROCAT register born between 1980 and 1994 were extracted and analysed. The crude birth prevalence rate for all NTD, spina bifida, anencephaly and encephalocoele were calculated for each year. Parameters measured were: sex ratio, stillbirth rate, proportion of low birth-weight babies (< 2500 g) and the proportion who were premature (< 37 weeks gestation).

Of 821 NTD cases, 419 (51.0%) had spina bifida, 322 (39.2%) had anencephaly, 69 (8.4%) had encephalocoele and 11 (1.3%) were iniencephalic. The crude birth prevalence of NTD decreased fourfold from 46.9/10,000 births in 1980 to 11.6/10,000 in 1994. The downward trend ceased during the early 1990's. Younger mothers had significantly higher rates of NTD affected births. Twenty two per cent of NTD cases had additional non-central nervous system anomalies. In 40 cases, there was a previous family history of NTD in siblings. Seasonal effects in birth prevalence were observed. Birth notification was the most frequent mechanism of ascertainment.

There was a marked fall in the birth prevalence of NTD during the 15 year period. This change was real and not accounted for by pre-natal screening and diagnostic practises with termination of pregnancy, which is not legally permissible in Ireland. Dietary factors may have had an influence. Rates of NTD in this region are still higher than many other parts of Europe. Primary prevention strategies through increased folic acid intake are necessary to further reduce NTD affected births.