title: Prenasal thickness to nasal bone length ratio: effectiveness as a second or third trimester marker for Down syndrome.
abstract: OBJECTIVE
  To assess the value of the prenasal thickness to nasal bone length ratio (PT/NBL) for detecting trisomy 21 (T21) after the first trimester.
  
  
  METHODS
  Two examiners blinded to fetal T21 status retrospectively measured prenasal thickness (PT) and nasal bone length (NBL) of T21 and control fetuses at 15-36 weeks' gestational age on two-dimensional images from all T21-screening ultrasounds from November 2010 to April 2013. ROC curve analysis and its diagnostic values determined the best cut-off value for the ratio. Interobserver reproducibility was assessed.
  
  
  RESULTS
  Good quality ultrasound profile images were available for 26 fetuses with T21 compared to 91 normal fetuses. The median PT/NBL ratio was 1.28 for T21 and 0.73 for control fetuses (p<0.0001). The PT/NBL ratio performed significantly better (AUC 0.99; 95%CI 0.97-1) than either PT (0.82; 0.73-0.91) or NBL (0.91; 0.85-0.98). The optimal PT/NBL ratio cut-off was 0.98, with a sensitivity of 88.5% [76.2-100%] and a specificity of 100%. Interobserver variability was low.
  
  
  CONCLUSIONS
  The PT/NBL ratio is a strong marker for detecting T21 in the second and third trimesters, significantly more effective than either indicator alone.
authors.affiliation: Maternal Fetal Medicine Department, Hôpital Paule-de-Viguier, CHU de Toulouse, Toulouse, France.
authors.forename: A
authors.initials: A
authors.lastname: Tournemire
authors.affiliation: Maternal Fetal Medicine Department, Hôpital Paule-de-Viguier, CHU de Toulouse, Toulouse, France.
authors.forename: M
authors.initials: M
authors.lastname: Groussolles
authors.affiliation: UMR 1027 INSERM, Université Paul Sabatier Toulouse III, Toulouse, France.
authors.forename: V
authors.initials: V
authors.lastname: Ehlinger
authors.affiliation: UMR 1027 INSERM, Université Paul Sabatier Toulouse III, Toulouse, France.
authors.forename: A
authors.initials: A
authors.lastname: Lusque
authors.affiliation: Maternal Fetal Medicine Department, Hôpital Paule-de-Viguier, CHU de Toulouse, Toulouse, France.
authors.forename: M
authors.initials: M
authors.lastname: Morin
authors.affiliation: Cabinet d'échographie des Pharaons, Toulouse, France.
authors.forename: J B
authors.initials: JB
authors.lastname: Benevent
authors.affiliation: UMR 1027 INSERM, Université Paul Sabatier Toulouse III, Toulouse, France; Clinical Epidemiology Unit, University Hospital, Toulouse, France.
authors.forename: C
authors.initials: C
authors.lastname: Arnaud
authors.affiliation: Maternal Fetal Medicine Department, Hôpital Paule-de-Viguier, CHU de Toulouse, Toulouse, France; UMR 1027 INSERM, Université Paul Sabatier Toulouse III, Toulouse, France. Electronic address: christophe.vayssiere@gmail.com.
authors.forename: C
authors.initials: C
authors.lastname: Vayssière
mesh_terms: D000328:Adult; D000465:Algorithms; D015415:Biomarkers; D001846:Bone Development; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000196:embryology / Q000453:epidemiology; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D009295:Nasal Bone / Q000000981:diagnostic imaging* / Q000196:embryology; D055171:Nasal Cartilages / Q000000981:diagnostic imaging* / Q000196:embryology; D015588:Observer Variation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016037:Single-Blind Method; D016216:Ultrasonography, Prenatal; D055815:Young Adult
chemical_list: D015415:Biomarkers
keywords: Nasal bone length; Prenasal thickness; Prenasal thickness–nasal bone length ratio; Prenatal ultrasound marker; Trisomy 21