DOWN-SYNDROME - EFFECTS OF DEMOGRAPHIC-FACTORS AND PRENATAL-DIAGNOSISON THE FUTURE LIVEBIRTH PREVALENCE

In northwest European countries maternal age is increasing. This will lead to an increase of the prevalence of Down syndrome conceptuses. Me anwhile, the increased use of prenatal cytogenetic diagnosis (PCD) wil l lead to a decrease in the prevalence of Down syndrome among livebirt hs. We were interested to know what the result of these two opposite d evelopments would be in the near future, and we describe here a model to quantify these processes and the resulting livebirth prevalence of Down syndrome. The model is demonstrated for The Netherlands from 1992 to 2001. The predicted livebirth prevalence for The Netherlands in 19 92 is 1.36 per 1000. Demographic factors will cause an increase to 1.7 6 per 1000 in 2001 with present indications for PCD and a utilization ratio of 50%. An increase of the utilization ratio to 90% in 2001 will lead to a prevalence of 1.22 per 1000, a little less than the present prevalence. Alternative screening programs, including maternal serum screening, could lead to a further decrease of the livebirth prevalenc e. The model described here can be used for evaluation of the conseque nces of alternative forms of Down syndrome screening.