IMPACT OF PRENATAL-DIAGNOSIS ON REVISED LIVEBIRTH PREVALENCE ESTIMATES OF DOWN-SYNDROME IN THE LOTHIAN REGION OF SCOTLAND, 1978-1992

Ramsay et al, [(1991) Biomed Pharmacother 45:267-272] reported on the livebirth prevalence of Down syndrome in the Lothian region of Scotlan d during 1978-1989. Their results suggested a temporal association bet ween the events of Chernobyl in April 1986 and a significant excess of cases in 1987. In the current study the data were extended for 3 year s and reanalyzed, a major objective being to correct for the different ial loss of fetuses with Down syndrome which occurs between prenatal d iagnosis and birth. Other objectives were to estimate the prevalence r eduction due to prenatal diagnosis, quinquennial maternal age-specific risk rates, and the level of ascertainment of cases. The reanalysis f ound a 12-year prevalence rate of 1.29 vs. the previous rate of 1.34, and a shift of the annual prevalence peak to 1988, with a reduced prev alence in 1987 compared to that found in the earlier study, The new re sults are less consistent in showing an association of Down syndrome c lustering with the Chernobyl accident. For the 15-year study period, a 23% overall reduction in prevalence occurred due to prenatal diagnosi s and elective abortion of affected fetuses, with a 50% reduction to w omen greater than or equal to 35 years of age. For 1988-1992, these re ductions were 33% and 60%, which are among the highest reported in the literature for these time periods. The estimated quinquennial materna l risk rates were very similar to others already reported, and the dat a are consistent with a high level of case ascertainment. Since these women are approaching the upper limits of fetal detection through adva nced maternal age alone, continued reduction in prevalence rates for D own syndrome through prenatal diagnosis and elective abortion will com e mostly from increased use of other (chemical) screening techniques n ow available. (C) 1996 Wiley-Liss, Inc.