The impact of prenatal diagnosis on the occurrence of chromosome abnormalities

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 Scotland during 1978-1989. Their results suggested a temporal association between 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 years and reanalyzed, a major objective being to correct for the differential loss of fetuses with Down syndrome which occurs between prenatal diagnosis and birth. Other objectives were to estimate the prevalence reduction due to prenatal diagnosis, quinquennial maternal age-specific risk rates, and the level of ascertainment of cases. The reanalysis found 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 prevalence in 1987 compared to that found in the earlier study. The new results are less consistent in showing an association of Down syndrome clustering with the Chernobyl accident. For the 15-year study period, a 23% overall reduction in prevalence occurred due to prenatal diagnosis and elective abortion of affected fetuses, with a 50% reduction to women > or = 35 years of age. For 1988-1992, these reductions were 33% and 60%, which are among the highest reported in the literature for these time periods. The estimated quinquennial maternal risk rates were very similar to others already reported, and the data are consistent with a high level of case ascertainment. Since these women are approaching the upper limits of fetal detection through advanced maternal age alone, continued reduction in prevalence rates for Down syndrome through prenatal diagnosis and elective abortion will come mostly from increased use of other (chemical) screening techniques now available.

Childhood deaths in Down's syndrome. Survival curves and causes of death from a total population study in Queensland, Australia, 1976 to 1985

Data have been obtained from a total population study of diagnosed Down's syndrome cases born in Queensland between 1976 and 1985. Survival curves show a survival rate to one year of 87.4% and no significant differences in such patterns over the two five year periods of the study. Survival curves comparing maternal age at birth, sex of the infant, and locality of birth also indicate that early death is unrelated to any of these factors. Congenital heart disease and respiratory infection are the most common causes of infant death.

Impact, logistics and prospects of traditional prenatal diagnosis

Traditional second trimester prenatal diagnosis (PD) by amniocentesis was introduced about 20 years ago. It is still the most frequently used procedure for this purpose. About 85% of all requests for PD are based on maternal age alone. The commonest indication is a maternal age of 35 or higher at delivery. Attempts are being made to improve utilization of the limited laboratory capacity by evaluating the indication for PD by combining age and other indicators, ie. maternal-serum-alpha-fetoprotein and unconjugated estriol. Chorionic villus sampling so far has appealed to an additional group of pregnant women rather than being a replacement for the older procedure. While the impact of PD on the individual woman and her family is great, it has limited impact on the prevalence of Down syndrome patients in the society. Of major concern is the impact of PD on the attitude to a pregnancy with a possibly affected child, on the attitude to induced abortion in general and on the acceptance of disabled individuals. The importance of proper genetic counseling including ethical issues is stressed.