title: Antenatal screening for Down's syndrome, trisomy 18, and trisomy 13: Reporting a single screening result for all three.
abstract: OBJECTIVE
  To compare the performance of antenatal screening for Down's syndrome (DS), trisomy 18 (T18), and trisomy 13 (T13) using a single risk of being affected by one of the three disorders, with the performance using separate risks for each disorder.
  
  
  METHODS
  Screening performance was estimated using Monte Carlo simulation based on published parameters for the Integrated, Combined, and Quadruple tests. Detection rates (DRs) were calculated using a single risk and separate risks for each disorder at given false-positive rates (FPRs).
  
  
  RESULTS
  With separate risks, using a 3% DS test FPR and 0.2% FPRs for the T18 and T13 tests, the overall FPRs for the Integrated and Combined tests are both 3.3%. For the same overall FPR (3.3%), the use of a single risk with the Integrated test increases the T13 DR from 76% to 82%, with unchanged DS and T18 DRs (94% and 92% respectively). With the Combined test, it increases the T13 and T18 DRs (from 89% to 91% and 77% to 81% respectively), with unchanged DS DR (85%). With separate risks, using a 5% DS test FPR and 0.2% FPRs for the T18 and T13 tests, the overall FPR for the Quadruple test is 5.4%. For the same overall FPR (5.4%), the use of a single risk increases the T18 DR from 61% to 67% with unchanged DS and T13 DRs (87% and 33% respectively).
  
  
  CONCLUSIONS
  Reporting a single risk estimate for the three disorders is less confusing than reporting separate risks and can yield the same or better screening performance.
authors: Wolfson Institute of Preventive Medicine, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, UK j.p.bestwick@qmul.ac.uk.
authors: Jonathan P
authors: JP
authors: Bestwick
authors: Wolfson Institute of Preventive Medicine, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
authors: Nicholas J
authors: NJ
authors: Wald
mesh_terms: D025063:Chromosome Disorders / Q000175:diagnosis* / Q000235:genetics; D002882:Chromosomes, Human, Pair 13; D002887:Chromosomes, Human, Pair 18; D004314:Down Syndrome / Q000175:diagnosis*; D005260:Female; D006801:Humans; D009010:Monte Carlo Method; D011247:Pregnancy; D011296:Prenatal Diagnosis; D014314:Trisomy / Q000175:diagnosis*; D000073839:Trisomy 13 Syndrome; D000073842:Trisomy 18 Syndrome
keywords: Down’s syndrome; antenatal screening; trisomy 13; trisomy 18