Objective To analyze the serological screening results of Down Syndrome（DS）in second trimester for6 341 cases in a hospital in Chongqing from 2012 to 2019

and to investigate the applicative value and influencing factor of serological screening on prenatal chromosome abnormality in second trimester.Methods A total of6 341 pregnant women underwent DS prenatal screening in a hospital in Chongqing from April 2012 to December2018 were selected as study objects.The serum alpha-fetoprotein（AFP）

free human chorionic gonadotropin（freeβ-hCG）and free estradiol（uE3）in the second trimester of 6 341 pregnant women were detected by chemiluminescence kit.Combined with antenatal examination

the value risk of fetal DS

18-Edwards′s Syndrome（ES）and neural tube defects（NTD）were counted by professional software.Results Among all study objects

531 were detected with high-risk chromosome abnormality

with a detection rate of 8.37%（531/6 341）.Among the high risk cases

403 cases were high risk of DS

with a positive rate of 6.36%（403/6 341）

62 cases were high risk of ES

with a positive rate of 9.78‰ （62/6 341）

and 66 cases were high risk of NTD

with a positive rate of10.41‰ （66/6 341）.The positive rate of DS in the age group 31 to 46（14.86%

262/5 392）was significantly higher than that in the age group 17 to 30（4.86%

141/949）

with statistically significant difference（P<0.05）.The positive rate of ES in the group aged 26 to 46（13.38‰ 47/3 513）was significantly higher than that in the group aged 17 to 25（5.30‰

15/2 828）

with statistically significant difference（P<0.05）.DS detection rate for pregnant women in different gestational weeks was different

with statistically significant difference（P<0.05）.DS detection rate in the 14 th week

15 th week and 21 st week was relatively higher.ES detection rate for pregnant women in different gestational weeks was different

with statistically significant difference（P<0.05）.ES detection rate in the 14 th week

15 th week and 16 th week was relatively higher.NTD detection rate for pregnant women in different gestational weeks had no statistically significant difference（P>0.05）.Differences of DS

ED and NTD in different body mass groups had no statistical significance（P>0.05）.Conclusion Serological screening in second trimester plays an important role in reducing birth defects.Fetus with an advanced-age mother has a higher risk of DS and ES

therefore

early pregnancy and scientific

standardized

timely and suitable prenatal screening can reduce the birth rate of birth defects and enhance the population quality.