Value and limits of ultrasonographic screening for trisomy 21 syndrome during the second and third trimesters of gestation

Objective: To investigate the value and limits of ultrasonographic screening for trisomy 21 syndrome during the second and third trimesters. Methods: Amniocentesis and cordocentesis were performed on 3110 and 187 pregnant women respectively with indications for prenatal diagnosis, in order to detect karyotype of the fetus during second trimester and late pregnancy. The detection rate of trisomy 21 syndrome was compared in pregnant women of different indications. Relationship between the ultrasonographic abnormalities and trisomy 21 syndrome was analyzed. Results: In chromosomal karyotypes analysis of 3110 pregnant women with amniocentesis, 41 (1.32%) trisomy 21 syndrome were detected. There were 98 in 3110 pregnant women with ultrasonographic abnormalities, 6 (6.12%) trisomy 21 syndrome were found within them, with a detection rate higher than that of the Down syndrome high risk group (0.98%) and advanced age group (0.58%, P<0.05). Within 187 pregnant women of chromosomal karyotypes analysis by cordocentesis, 9(4.81%) trisomy 21 syndrome were detected. Among 128 in 187 pregnant women with ultrasonographic abnormalities, 5 trisomy 21 syndrome were found and the detection rate was 3.91% (P<0.05). Conclusion: During the second and third trimesters, ultrasonography has great value, but still has limits in screening for trisomy 21 syndrome.