The impact of antenatal screening for Down syndrome in Western Australia: 1980-1994.

Since the early 1970s, women in Western Australia have been screened for fetal Down syndrome risk on the basis of maternal age. Women 35 years of age or more at delivery, were offered fetal karyotyping with genetic diagnostic testing via amniocentesis or chorionic villus sampling. An increase in the prevalence of Down syndrome of 3.9% per year (95% confidence interval: 1.8-6.0%) was observed between 1980 and 1994, almost all of which was accounted for by increased maternal age. In 1991, a maternal serum screening (MSS) programme for Down syndrome was first implemented in Western Australia and has since evolved in 6 separate laboratories providing Down risk assessment in 1994. The gradual introduction of MSS programmes had little discernible impact until 1994, when 38% of Down syndrome fetuses were ascertained as a result of increased-risk MSS tests and the birth prevalence of Down syndrome decreased significantly. In this report, we review antenatal screening programmes and their impact on the birth prevalence of Down syndrome in Western Australia.