Abstract: Objective: To investigate the value of second trimester prenatal serological screening for Down's syndrome by analyzing the positive rate of serological screening and the detection rate of Down's syndrome. Methods: From January to December 2014, prenatal serological screening for Down's syndrome was performed in 19 718 pregnant women in 14-21 weeks of pregnancy. Combined detection of alpha fetoprotein (AFP), β-human chorionic gonadotropin (β-hCG) and unconjugated estriol(uE₃) was performed on Beckman Access 2 Automatic Chemiluminescence Analyzer. Calculated the multiples of median (MoM) of above three indices and in coordinating with maternal age, body weight and weeks of pregnancy to predict the risk of 21-trisomy, open spine bifida (OSB), 18-Trisomy, and the pregnancy outcome was followed. Results: In the 19 718 pregnant women, serological triple screening revealed that 1 264 pregnant women were in high risk and had a positive screening rate of 6.41%. Among 18 660 pregnant women under 35 years old, 1 015 were in high risk and had a positive screening rate of 5.44%;; while for 1 058 pregnant women over 35 years old, 249 cases were in high risk and had a positive screening rate of 23.53%. Follow-up study showed that 11 pregnant women had baby with Down's syndrome, including 9 with screening positive and 2 with screening negative. The detection rate of 21-Trisomy was 82%. Follow-up also confirmed 2 cases of 18-Trisomy and 6 cases of other deformities. Conclusions: In considering the detection rate, economic aspect and operability of laboratory, serological screening in second trimester is still an important approach for screening Down′s syndrome, besides, 18-Trisomy, OSB and some other deformities can also been screened.

Key words: Down′s syndrome, Positive detection rate, Positive rate of screening