Abstract: Objective To study the second trimester prenatal screening operation in Yuhang district of Hangzhou,and to evaluate the significance of using trimester serum mark of screening for finding chromosomal abnormalities and neural tube defects. Methods A total of 44 410 cases were collected during 2006 to 2011 from five hospitals in Yuhang,informed consent and voluntary to participate.Time- resolved fluorescence method(DELFIA) was used to measure concentration of α-fetoprotein(AFP) and Free β human chorionic gonadotropin (free-β-hCG) of cases’ serum.Risk 2T computer software was used to evaluate the risk of Down syndrome(DS),Edward syndrome(ES) and neural tube defects(NTD).Karyotype analysis was done after amniocentesis or umbilical cord blood puncture to high risk of DS,ES cases.3D color Doppler ultrasound was used to detect the low risk of NTD cases. Results The rate of prenatal screening and the absolute number of prenatal diagnosis increased year by year,while the proportion of amniocentesis and umbilical cord blood puncture and the diagnosis rate decreased.1 945 cases of 44 410 cases had high risk,and the total positive rate was 4.38%.Total 10 cases of DS,6 cases of 18-trisomy,13 cases of NTD and 39 cases of other abnormalities of fetus were diagnosed from high risky pregnant women;4 cases of DS and 9 cases of NTD were diagnosed from low risky pregnant women. Conclusion Free prenatal screening is an effective means to improve the prenatal screening rate; the application of trimester Down’s syndrome screening combined with prenatal diagnoses is an effective way to reduce birth defects.