title: Model predicted Down syndrome detection rates for nuchal translucency screening in twin pregnancies.
abstract: OBJECTIVE
  To estimate the Down syndrome detection rate for nuchal translucency (NT) screening in twins when fetus-specific risk allows for between-fetus NT correlation.
  
  
  METHODS
  The between-fetus correlation coefficient of log NT, in multiples of the median (MoM), was estimated from a series of 977 unaffected twins scanned at a single centre. Results were expressed in multiples of the normal median using a curve derived from 515 unaffected singleton pregnancies at the same centre. A screening result was classified as positive if the risk for at least one fetus exceeded the cut-off. Detection rates were estimated for a fixed 1-5% false-positive rate, at different gestational weeks, separately for risk calculation using an algorithm which takes account of between-fetus NT correlation or not.
  
  
  RESULTS
  The correlation coefficient in unaffected pregnancies was 0.43 (P < 0.0001) and estimated to be 0.23 and 0.11 in discordant and concordant twins. At 12 weeks of gestation, the model predicted detection rate for a 3% false-positive rate was 68% when between-fetus correlation is not taken into account, increasing to 73% when it is applied. Similarly, for other false-positive rates and gestational weeks there was a predicted 4-6% increase in detection.
  
  
  CONCLUSIONS
  Using a fetus-specific Down syndrome risk algorithm leads to a worthwhile increase in detection.
authors: Department of Obstetrics and Gynecology, Assaf Harofe Medical Center, The Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel. intposgr@post.tau.ac.il
authors: Ron
authors: R
authors: Maymon
authors: Hadar
authors: H
authors: Rosen
authors: Ohad
authors: O
authors: Baruchin
authors: Arie
authors: A
authors: Herman
authors: Howard
authors: H
authors: Cuckle
mesh_terms: D000328:Adult; D000465:Algorithms; D004200:Diseases in Twins / Q000175:diagnosis* / Q000000981:diagnostic imaging; D004314:Down Syndrome / Q000175:diagnosis* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D015233:Models, Statistical; D009333:Neck / Q000000981:diagnostic imaging / Q000196:embryology; D048208:Nuchal Translucency Measurement / Q000379:methods* / Q000706:statistics & numerical data; D011237:Predictive Value of Tests; D011247:Pregnancy