An 8-center study to evaluate the utility of midterm genetic sonograms among high-risk pregnancies

Objective. A multicenter study was undertaken to evaluate the diagnostic efficacy of a genetic sonogram. Methods. Eight centers provided data on 176 pregnancies complicated by fetal Down syndrome. One hundred thirty-four pregnancies were considered high risk because of advanced maternal age (>35 years), and 42 were considered high risk for having "abnormal" triple-screen results (risk >1:250). Each center provided fetal biometric data, information regarding the presence or absence of major structural abnormalities, and between 3 and 6 additional ultrasonographic markers for trisomy 21. The heterogeneity of our 8 independent "sensitivity estimates" was evaluated by Poisson regression, and a single combined estimate of the sensitivity was calculated. Results. Of the total 176 cases of trisomy 21, 125 fetuses (71.0%) had either an abnormal long bone length (femur length, humerus length, or both), a major structural abnormality, or a Down syndrome marker. The combined diagnostic sensitivity was 71.6%, with a range of 63.6% (7 of 11) to 80% (8 of 10). Five centers had sensitivity estimates falling between 64% and 76%. The sensitivity of individual markers varied between 3% (sandal gap) and 46.5% (nuchal skin fold thickness). A condensed regimen of nuchal skin fold thickness, femur length, and a standard anatomic survey would screen in 56.8% of fetuses with Down syndrome. Conclusions. This 8-center study that included many fetuses with Down syndrome validates the concept that the genetic sonogram can be used to better adjust the Down syndrome risk for high-risk patients.