SCREENING FOR FETAL TRISOMY-21 IN THE FIRST TRIMESTER OF PREGNANCY - MATERNAL SERUM-FREE BETA-HCG AND FETAL NUCHAL TRANSLUCENCY THICKNESS

The aim of this prospective study was to measure the contribution of m aternal serum free beta-human chorionic gonadotropin (beta-hCG) in a s creening program for fetal trisomy 21 based on fetal nuchal translucen cy in the first trimester of pregnancy. The maternal serum was collect ed at the time of the ultrasound scan and assayed without knowledge of the nuchal translucency measurement or karyotype. A total of 2529 pre gnancies were examined (normal group, n = 2427; trisomy 21 group, n = 102). Maternal serum free beta-hCG was significantly associated with g estational age and maternal weight. In the trisomy 21 group the free b eta-hCG was significantly higher than in the normals, being above the 95th centile in 29% of the cases. There was no significant association between the deviation from the mean for free beta-hCG and nuchal tran slucency thickness in either the normal or the trisomy 21 groups. When maternal serum free beta-hCG was added to a model based on maternal a ge and fetal nuchal translucency thickness, the detection rare for tri somy 22 was increased from 80% to 85%.