Abstract: Objective To evaluate the function and value of prenatal screening in the diagnosis of 21-trisomy syndrome, 18-trisomy syndrome and neural tube defect. Methods Serum samples were collected during middle period pregnancy(15-20 week) and free-β-human chorionic gonadot ropin (free-β-HCG) and alphafetoprotein(AFP) level were determined by time-resolved fluoroimmunoassay(TR-FIA, or DELFIA) method. In combination with gestational age, weight, and age, we evaluated the risk assessment with assessment software. The pregnant women found with high risk in screening by eugenic genetic counseling were examined by amniocentesis and prenatal ultrasound. Results Of the 28 450 pregnant women through prenatal screening,1000 were found to have high risk, the positivity rate being 3.51%. The calculated results showed that 598 and 136 cases were with high risk of 21-trisomy syndrome and 18-trisomy syndrome in 28 540 test samples, respectively. Among high risk pregnant women who voluntarily accepted amniocentesis, 7 and 4 cases were with high risk of 21 trisomy syndrome and 18 trisomy syndrome, respectively. Two cases of anencephalus and 7 cases of spina bifida were detected by prenatal ultrasound. Three hundred and eleven cases of birth defects were detected in the follow-up pregnant women by prenatal screening. Conclusion The results in this study indicate that prenatal screening of middle period serum of pregnant women combined with prenatal diagnosis can reduce the risk of birth defects incidence and is the effective screening method to reduce birth defect.