Best second trimester sonographic markers for the detection of trisomy 21

We analyzed all genetic sonograms obtained during a 6 year period to establ ish the independent ability of the following sonographic markers of aneuplo idy in the diagnosis of trisomy 21: structural anomalies, cardiac abnormali ties, nuchal fold thickness of 6 mm or greater, bowel echogenicity, choroid plexus cysts, and renal pyelectasis. With the exception of bowel echogenic ity and choroid plexus cysts, the sonographic markers were more common in t risomy 21 than euploid fetuses (all P < 0.001). Logistic regression analysi s demonstrated that cardiac anomalies (odds ratio = 255; 95% confidence int erval, 25, 2592), other structural anomalies (odds ratio = 25; 95% confiden ce interval, 6, 97), and nuchal fold thickness of 6 mm or greater (odds rat io = 13; 95% confidence inter val, 3, 50) were the only independent predict ors of trisomy 21. The false-positive rate and sensitivity were 5.3% (48 of 898) and 59.2% (13 of 22), respectively, when any of the sonographic marke rs significant at univariate analysis was considered, and 3.1% (28 of 898) and 54.5% (12 of 22), respectively, when any of the predictors at multivari ate analysis was present. Because a considerable overlap of sonographic mar kers exists among trisomy 21 fetuses, use of those that are not independent predictors leads to an increase in false-positive rate without a gain in s ensitivity.