Second trimester maternal serum screening for Down's syndrome in women of advanced maternal age: a multi-center prospective study

Abstract

To evaluate the performance characteristics of the second trimester double test for the detection of fetal Down's syndrome (DS) in women of advanced maternal age (AMA). We undertook a prospective nation-wide multi-centered study and chose alpha-fetoprotein (AFP) and free beta-subunit of human chorionic gonadotrophin (free beta-hCG) as the serum markers. Between May 2004 and September 2006, 12 centers participated in the collection and analysis of maternal serum AFP and free beta-hCG. Patients with an increased risk of DS (> or = 1/270) were offered genetic amniocentesis. Follow up of the outcome of all pregnancies was obtained. Patients were divided into two groups, the AMA group and the non-AMA group and the screening efficiency was evaluated in both groups. A total of 66 132 singleton pregnancies were included in the study, and there were 3610 (5.46%) AMA women. The median maternal age of AMA women was 36.8years (35 - 47 years). At a cut-off of 1/270, in the AMA group, the number of positive cases screened was 727 and 22 cases of fetal DS were detected; the number of negative cases screened was 2883, and no fetal DS was found. In the non-AMA group, the number of positive cases screened was 4743 and 69 cases of fetal DS were detected; the number of negative cases screened was 57 779, and 6 cases of fetal DS were diagnosed postnatally. In AMA group, the detection rate (DR), false positive rate (FPR) and odds of being affected given a positive result (OAPR) were 100%, 19.7% and 3.0% respectively. In the non-AMA group, the DR, FPR and OAPR were 92.0%, 7.5% and 1.5% respectively. The double-marker test using AFP and free beta-hCG is an effective screen strategy for second-trimester detection of Down syndrome in AMA women.