Triple marker (alpha-fetoprotein, unconjugated estriol, human chorionic gonadotropin) versus alpha-fetoprotein plus free-beta 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 (alpha-fetoprotein, unconjugated estriol, human chorionic gonadotropin) with alpha-fetoprotein plus free beta-human chorionic gonadotropin.

STUDY DESIGN: Free beta-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 beta-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 alpha-fetoprotein plus free beta-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 alpha-fetoprotein plus free beta-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 alpha-fetoprotein plus free beta-human chorionic gonadotropin.

CONCLUSION: The detection rate of fetal Down syndrome was greater by use of a triple marker screen than when using alpha-fetoprotein plus free beta-human chorionic gonadotropin. Our data do not support the claims of other studies that suggest that alpha-fetoprotein plus free beta-human chorionic gonadotropin is superior to triple markers.