The epidemiology of down syndrome in four counties in Ireland 1981-1990

Abstract

Background: We conducted a descriptive epidemiological study of Down syndrome (DS) in the four Irish counties (Dublin, Kildare, Wicklow and Galway) covered by EUROCAT registries of congenital malformations for the years 1981–1990. Methods: EUROCAT registries, which cover defined populations, use multiple sources for case ascertainment. All DS cases born between 1 January 1981 and 31 December 1990 to mothers resident in the four counties were identified. Crude birth prevalence rates and maternal agestandardized rates (SPRs) were calculated for each county and for each year in the study period. The prevalence of DS by maternal age grouped in five-year periods and the risk for each five-year group were also estimated. Results: The crude birth prevalence for the four counties was 18⋅5/10 000 for all births and 18⋅3 for live births. There was a fall in the total number of DS births over the decade, but less change in the crude birth prevalence owing to an increase in the proportion of mothers aged 35 +. Galway had the highest crude birth prevalence of DS (23⋅5/10 000) but the SPR was within average for the four counties as a whole - 110⋅3, 95 per cent confidence interval (Cl) 86⋅7–139. The risk of having a DS child increased 70-fold from 1:1841 at age 15–19 to 1:26 at 45 years or older. Nearly half of all DS cases (47⋅4 per cent) had at least one additional anomaly. Conclusions: The parts of Ireland covered by EUROCAT have a high birth prevalence of DS births as compared with some other countries, but the maternal age-specific rates are not substantially different from those in large international studies. © 1996, Oxford University Press.