AGE-INDEPENDENT INDEXES IN 2ND-TRIMESTER SERUM SCREENING FOR DOWNS-SYNDROME ARE USELESS

Serum screening for fetal Down's syndrome in the second trimester is f ar more efficient in older mothers than in younger ones because the ri sk calculation is based on maternal age. In recent publications, sever al authors have tried to better the 'classical' test for Down's syndro me screening by creating an age-independent index. This procedure, how ever, requires the assumption that at least for one parameter the mean MOM or the variance is not constant in relation to maternal age, lead ing to a smaller overlap in younger women. This study, based on almost 3000 normal cases and 161 cases with Down's syndrome, could not demon strate any relationship between maternal age and MOM distribution for alpha-fetoprotein, unconjugated oestriol, total human chorionic gonado tropin (hCG), and free beta hCG. We conclude that for a constant false -positive rate,the detection rate of the 'classical' test for Down's s yndrome screening in younger women cannot be bettered by creating an a ge-independent index.