title: First-trimester risk calculation for trisomy 13, 18, and 21: comparison of the screening efficiency between 2 locally developed programs and commercial software.
abstract: BACKGROUND
  Reliable individual risk calculation for trisomy (T) 13, 18, and 21 in first-trimester screening depends on good estimates of the medians for fetal nuchal translucency thickness (NT), free β-subunit of human chorionic gonadotropin (hCGβ), and pregnancy-associated plasma protein-A (PAPP-A) in maternal plasma from unaffected pregnancies. Means and SDs of these parameters in unaffected and affected pregnancies are used in the risk calculation program. Unfortunately, our commercial program for risk calculation (Astraia) did not allow use of local medians. We developed 2 alternative risk calculation programs to assess whether the screening efficacies for T13, T18, and T21 could be improved by using our locally estimated medians.
  
  
  METHODS
  We established these estimates from 19 594 women with singleton pregnancies and from 100 pregnant women carrying a fetus affected with trisomy (11 with T13, 23 with T18, and 66 with T21). All measured values were recalculated to a multiple of the median (MoM) and log(10) transformed; the mean and SD were calculated for each group.
  
  
  RESULTS
  At a given risk cutoff value, we observed a slight improvement in detection rate (DR) for T13, T18, and T21 for a slightly higher false-positive rate (FPR) compared with the commercial program. The lower FPR in the commercial program was caused mainly by an inaccuracy in the PAPP-A median.
  
  
  CONCLUSIONS
  Center-specific medians for NT, hCGβ, and PAPP-A should be used in risk calculation programs to ensure high DRs and low FPRs for all 3 trisomies at a given risk cutoff.
authors.affiliation: Department of Clinical Biochemistry, Hvidovre Hospital, University of Copenhagen, Denmark. steen.soerensen@hvh.regionh.dk
authors.forename: Steen
authors.initials: S
authors.lastname: Sørensen
authors.forename: Günther
authors.initials: G
authors.lastname: Momsen
authors.forename: Karin
authors.initials: K
authors.lastname: Sundberg
authors.forename: Lennart
authors.initials: L
authors.lastname: Friis-Hansen
authors.forename: Finn Stener
authors.initials: FS
authors.lastname: Jørgensen
mesh_terms: D000293:Adolescent; D000328:Adult; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D025063:Chromosome Disorders / Q000175:diagnosis; D002882:Chromosomes, Human, Pair 13; D002887:Chromosomes, Human, Pair 18 / Q000235:genetics*; D004314:Down Syndrome / Q000175:diagnosis*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D018570:Risk Assessment; D012984:Software; D014314:Trisomy / Q000175:diagnosis; D000073839:Trisomy 13 Syndrome; D055815:Young Adult
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A