title: First-trimester nuchal translucency, nasal bones, and trisomy 21 in selected and unselected populations.
abstract: OBJECTIVE
  The purpose of this study was to assess the role of fetal nasal bones evaluation in first-trimester screening for trisomy 21 in selected and unselected pregnancies.
  
  
  METHODS
  Visualization of the nasal bones was attempted in women attending for routine nuchal translucency screening (unselected population, n = 7116, 12 cases of trisomy 21), as well as in high-risk pregnancies referred to our tertiary care center (selected population, n = 510, 23 cases of trisomy 21).
  
  
  RESULTS
  The sensitivity, specificity, positive and negative predictive value of absent nasal bones for trisomy 21 were 16.7%, 97.3%, 1.1%, 99.8% and 47.6%, 95.3%, 33.3%, 97.4% in the unselected and selected population, respectively. At logistic regression analysis including nuchal translucency and nasal bones findings, the latter resulted to be an independent predictor of trisomy 21 in the selected but not in the unselected population.
  
  
  CONCLUSIONS
  First-trimester nasal bones assessment for trisomy 21 screening has a very different performance in selected and unselected pregnancies.
authors.affiliation: Division of Obstetrics and Gynaecology, St George's, University of London, United Kingdom. fprefumo@sgul.ac.uk
authors.forename: Federico
authors.initials: F
authors.lastname: Prefumo
authors.forename: Shanthi
authors.initials: S
authors.lastname: Sairam
authors.forename: Amarnath
authors.initials: A
authors.lastname: Bhide
authors.forename: Baskaran
authors.initials: B
authors.lastname: Thilaganathan
mesh_terms: D000293:Adolescent; D000328:Adult; D004314:Down Syndrome / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D008875:Middle Aged; D009295:Nasal Bone / Q000000981:diagnostic imaging*; D009333:Neck / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal