Evaluation of first trimester maternal serum and ultrasound screening for Down's syndrome in Eastern and Northern Finland

The current trend in prenatal diagnosis is that trisomy screening is being moved to the first trimester and ultrasonographic nuchal translucency measu rement is included in risk calculation. It is likely that biochemical scree ning in the second trimester will gradually be given up. In Eastern and Nor thern Finland, during the year 1999 we offered first-trimester ultrasonogra phic and serum screening for trisomy 21, with measurements of maternal seru m PAPP-A and beta -hCG. A total of 2515 pregnant women participated in the screening, yielding the detection of eight foetuses with Down's syndrome. S ix affected foetuses (75%) were detected by means of first-trimester serum screening. Since we were in the phase of collecting data for the Finnish me dians for PAPP-A and beta -hCG, the women were not given the estimates of r isk for trisomy 21. Only 1602 of the 2515 enrolled women had the combinatio n of first-trimester ultrasonographic and serum screening performed, and in that group there were five foetuses with Down's syndrome. The combination ultrasonographic and serum approach yielded a Down's syndrome detection rat e of 80% (four out of five) with a 5% false positive rate, whereas in nucha l translucency based-screening the detection rate was 60%, with a 5% false positive rate.