Maternal serum screening for Down syndrome in the first trimester: Experience from Belarus

We have carried out a large retrospective study of alpha-fetoprotein (AFP), free-beta human chorionic gonadotrophin (hCG) and pregnancy-associated pla sma protein (PAPP-A) in the first trimester of pregnancy. Unlike other stud ies all women had routine ultrasound dating, carried out during a nuchal tr anslucency measurement project. A total of 13 477 serum samples were tested for AFP and 11 659 for free beta-hCG. A subset of 1564 samples from unaffe cted pregnancies were also tested for PAPP-A on a case-control basis. All t hree markers were also determined in 31 samples from pregnancies with Down syndrome. Equations were derived to express results in multiples of the med ian using both gestational age and crown-rump length and to adjust for mate rnal weight. Statistical modelling with Gaussian distribution parameters ob tained in the study were used to predict the detection rate for a 5 per cen t false-positive rate. The predicted rates were: 73.7 per cent for all thre e markers; 69.1 per cent for PAPP-A and free beta-hCG; 47.4 per cent for PA PP-A and AFP; 57.6 per cent for free beta-hCG and AFP. As these rates are s imilar to those in the second trimester, health planners may now want to co nsider a change in policy from second-trimester to first-trimester screenin g with biochemical markers. Copyright (C) 1999 John Wiley & Sons, Ltd.