Impact of prenatal diagnosis on the prevalence of live births with Down syndrome in the eastern half of Switzerland 1980-1996.

OBJECTIVES AND METHODS To investigate the impact of prenatal diagnosis on trisomy 21 live births, we collected all prenatal and postnatal trisomy 21 cases (n = 1096) in the eastern half of Switzerland for the years 1980-1996. RESULTS Despite increasing prenatal detection rates of trisomy 21 foetuses (an increase of 169% in the last 5 versus the first 5 years of the study period) and subsequent termination of pregnancies, the number of liveborn Down syndrome children remained constant. The reason is a shift towards a higher mean maternal age from 28 to 30 years between 1980 and 1996. If mean maternal age at delivery was considered, the observed increase of trisomy 21 conceptions matched well with the calculated figures. CONCLUSION If the tendency to have pregnancies at a more advanced age continues and if the use of prenatal diagnosis does not increase, an increase in incidence of Down syndrome liveborns may be expected in the first decades of the 21st century.