[Second trimester maternal serum screening for Down's syndrome in mainland China: a multi-center prospective study]

To evaluate the performance characteristics of the second trimester double-marker test for the detection of fetal Down's syndrome in mainland China.This prospective national multi-centered study used alpha-fetoprotein (AFP) and free beta-subunit of human chorionic gonadotrophin (free beta-hCG) as the serum markers. From May 2004 to September 2006, 11 centers participated in the collection and analysis of maternal serum AFP and free beta-hCG between 14 and 20(+6) weeks of pregnancy. The screening results were calculated using the standard algorithm based on the standard database provided with the analytic software. Patients with an increased risk of Down's syndrome pregnancy (or = 1/270) were offered genetic amniocentesis. Outcomes of all pregnancies were obtained.A total of 66 132 singleton pregnancies were included in the study. The median maternal age was 27 years. At a cut-off of 1 in 270, the detection rate (DR) based on a Caucasian database was 72% corresponding to a false positive rate (FPR) of 5%, and the DR based on the Chinese database was raised to 76% corresponding to an FPR of 5%.The double-marker test using AFP and free beta-hCG is an effective screen strategy for second-trimester detection of fetal Down's syndrome in mainland China. Ethnic variance exists between the Caucasian and Chinese populations. The accuracy of screening is increased by the use of race-specific medians.