title: The "genetic sonogram": comparison of the index scoring system with the age-adjusted US risk assessment.
abstract: OBJECTIVE
  To compare two ultrasonographic (US) methods for prenatal detection of fetal Down syndrome.
  
  
  METHODS
  Genetic amniocentesis was successfully performed in 3,303 consecutive women with high-risk pregnancies (mean gestational age, 17.1 weeks). All patients underwent a complete "genetic US" examination prospectively. Risk was assessed by using (a) various modifications of the index scoring system (ISS) and (b) the age-adjusted US risk assessment (AAURA).
  
  
  RESULTS
  The prevalence of Down syndrome in this population was 1.6% (53 of 3,303). By using a threshold of at least 2 points to detect trisomy 21, the best ISS had a sensitivity of 45.3%, false-positive rate of 4.9%, likelihood ratio of 9.3, and positive predictive value in the high-risk population in this study of 13.3%. Lowering the threshold to 1 point increased the sensitivity to 60.4% but increased the false-positive rate to 15.8%. Adding points for age increased the sensitivity to 67.9% but increased the false-positive rate to 24.3%. Results of using AAURA to detect trisomy 21 were nearly identical, with a sensitivity of 43.4% and false-positive rate of 4.9% at a 1 in 36 risk threshold and a sensitivity of 69.8% and false-positive rate of 26.1% at a 1 in 200 threshold. Trisomies 18 and 13 were detected with sensitivities of 80.0% and 100.0%, respectively, with either system.
  
  
  CONCLUSIONS
  The modified ISS and AAURA are equivalent in screening for Down syndrome, with detection of approximately half of all trisomy 21 fetuses at a 5% false-positive rate.
authors.affiliation: Department of Radiology, Division of Ultrasound, University of Washington Medical Center, Seattle, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Winter
authors.forename: S B
authors.initials: SB
authors.lastname: Uhrich
authors.forename: V L
authors.initials: VL
authors.lastname: Souter
authors.forename: D A
authors.initials: DA
authors.lastname: Nyberg
mesh_terms: D000328:Adult; D000649:Amniocentesis / Q000706:statistics & numerical data; D004314:Down Syndrome / Q000000981:diagnostic imaging; D005189:False Positive Reactions; D005260:Female; D005820:Genetic Testing / Q000379:methods*; D005865:Gestational Age; D006801:Humans; D016013:Likelihood Functions; D008423:Maternal Age; D011446:Prospective Studies; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods / Q000706:statistics & numerical data; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods* / Q000706:statistics & numerical data