title: Nuchal translucency: an ultrasound marker for fetal chromosomal abnormalities.
abstract: BACKGROUND
  The literature shows an association between several ultrasound markers and chromosome abnormality. Among these, measurement of nuchal translucency has been indicated as a screening method for aneuploidy. The trisomy of chromosome 21 has been most evaluated.
  
  
  OBJECTIVE
  To define the best fixed cutoff point for nuchal translucency, with the assistance of the ROC curve, and its accuracy in screening all fetal aneuploidy and trisomy 21 in a South American population.
  
  
  METHODS
  Validation of a diagnostic test.
  
  
  METHODS
  This study was carried out at the State University of Campinas, Campinas, Brazil.
  
  
  METHODS
  230 patients examined by ultrasound at two tertiary-level private centers, at 10 to 14 weeks of gestation.
  
  
  METHODS
  The participants consisted of all those patients who had undergone ultrasound imaging at 10 to 14 weeks of gestation to measure nuchal translucency and who had had the fetal or neonatal karyotype identified.
  
  
  METHODS
  Maternal age, gestational age, nuchal translucency measurement, fetal or neonatal karyotype.
  
  
  RESULTS
  Prevalence of chromosomal defects - 10 %; mean age - 35.8 years; mean gestational age - 12 weeks and 2 days; nuchal translucency (NT) thickness - 2.18 mm. The best balance between sensitivity and specificity were values that were equal to or higher than 2.5 mm for overall chromosomal abnormalities as well as for the isolated trisomy 21. The sensitivity for overall chromosomal abnormalities and trisomy 21 were 69.5 % and 75 %, respectively, and the positive likelihood ratios were 5.5 and 5.0, respectively.
  
  
  CONCLUSIONS
  The measurement of nuchal translucency was found to be fairly accurate as an ultrasound marker for fetal abnormalities and measurements equal to or higher than 2.5 mm were the best fixed cutoff points.
authors.affiliation: Faculty of Medical Sciences, Universidade Estadual de Campinas, Campinas, Brazil. glacacio@uol.com.br
authors.forename: G L
authors.initials: GL
authors.lastname: Acácio
authors.forename: R
authors.initials: R
authors.lastname: Barini
authors.forename: W
authors.initials: W
authors.lastname: Pinto Júnior
authors.forename: R L
authors.initials: RL
authors.lastname: Ximenes
authors.forename: H
authors.initials: H
authors.lastname: Pettersen
authors.forename: M
authors.initials: M
authors.lastname: Faria
mesh_terms: D000328:Adult; D000367:Age Factors; D000782:Aneuploidy; D001938:Brazil; D002891:Chromosomes, Human, Pair 21 / Q000000981:diagnostic imaging / Q000235:genetics; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000235:genetics*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007621:Karyotyping; D008423:Maternal Age; D008875:Middle Aged; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D015995:Prevalence; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal