Total hCG Versus Free β-hCG Combined with Alpha-fetoprotein for Down Syndrome Screening in Taiwan

OBJECTIVE: The purpose of this study was to compare the effectiveness between total human chorionic gonadotropin (hCG) and free beta-hCG in two-marker Down syndrome screening programs during the second trimester in a Taiwanese population. MATERIALS AND METHODS: From a multicenter collaborative study, we investigated the second-trimester maternal serum levels of total hCG from 67 data, free beta-hCG from 72 and alpha-fetoprotein (AFP) from 96 obtained from Taiwanese pregnant women carrying fetuses with Down syndrome. RESULTS: High total hCG and free beta-hCG, as well as low AFP levels, were found with median values of 2.06, 2.49 and 0.77 multiples of the median (MoM), respectively. At a 5% false-positive rate, total hCG and free beta-hCG could detect 31% and 43% of Down syndrome pregnancies, respectively, whilst AFP alone could detect only 15% of affected cases. When combined with maternal age-specific risk, total hCG could achieve a 52% detection rate, free beta-hCG a 54% and AFP a 39%. Combined total hCG and AFP achieved a detection rate of 55%, and combined free beta-hCG and AFP achieved a rate of 60%. CONCLUSION: The measurement of free beta-hCG is more beneficial than total hCG in serum screening for Down syndrome during the second trimester of pregnancy.