Objective: 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).
Methods: 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.
Results: 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.
Conclusion: 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.