Triple marker (α-fetoprotein, unconjugated estriol, human chorionic gonadotropin) versus α-fetoprotein plus free-β subunit in second-trimester maternal serum screening for fetal Down syndrome: A prospective comparison study

OBJECTIVE: Our purpose was to compare the efficacy of triple-marker screening (α-fetoprotein, unconjugated estriol, human chorionic gonadotropin) with α-fetoprotein plus free β-human chorionic gonadotropin. STUDY DESIGN: Free β-human chorionic gonadotropin was concurrently assayed in 2349 maternal serum samples. Trivariate and bivariate algorithms were used to calculate the risk for fetal Down syndrome by the two protocols. Free β-human chorionic gonadotropin from 12 cases of fetal Down syndrome previously screened with the triple marker was retrospectively assayed. RESULTS: Mean maternal age of our study was 29.8 years (range 14 to 51 years). The initial screen-positive rate with the triple marker was 8.0% compared with 12.8% for α-fetoprotein plus free β-human chorionic gonadotropin. All three cases of fetal Down syndrome ascertained in our prospective study were detected by the triple marker; in contrast, one of three was detected by α-fetoprotein plus free β-human chorionic gonadotropin. By adding 12 additional cases of fetal Down syndrome, 12 of 15 (80%) were screen positive with triple marker and nine of 15 (60%) were screen positive with α-fetoprotein plus free β-human chorionic gonadotropin. CONCLUSION: The detection rate of fetal Down syndrome was greater by use of a triple marker screen than when using α-fetoprotein plus free β-human chorionic gonadotropin. Our data do not support the claims of other studies that suggest that α-fetoprotein plus free β-human chorionic gonadotropin is superior to triple markers.