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An 8-Center Study to Evaluate the Utility of Midterm Genetic Sonograms Among High-Risk Pregnancies

Departments of Obstetrics and Gynecology and Preventive Medicine and Biostatistics, University of Colorado School of Medicine, Denver, Colorado (J.C.H., D.C.L., W.H.P.); Fetal Diagnostic Center of Pasadena and Alfigen, Genetics Institute, Pasadena, California (G.D.); Department of Obstetrics and Gynecology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts (B.R.B.); Pacific Northwest Diagnostic Ultrasound and University of Washington School of Medicine, Seattle, Washington (D.A.N.); Department of Maternal-Fetal Medicine and Obstetrics, University of Medicine and Dentistry of New Jersey, New Brunswick, New Jersey (A.M.V.); Department of Obstetrics and Gynecology, Cedars-Sinai Medical Center, University of California Los Angeles School of Medicine, Los Angeles, California (L.D.P., D.C.); Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Yale University School of Medicine, New Haven, Connecticut (R.O.B.-S.); and Division of Maternal-Fetal Medicine, Eastern Virginia Medical School, Norfolk, Virginia (A.Z.A.) USA.

Address correspondence and reprint requests to John C. Hobbins, MD, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, 4200 E Ninth Ave, Mail Stop B198, Denver, CO 80262 USA.

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.

Key Words: Down syndrome • prenatal diagnosis • second trimester • ultrasonography

Abbreviations: AMA, advanced maternal age • EIF, echogenic intracardiac focus • MSTS, maternal serum triple-screen • NSFT, nuchal skin fold thickness

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