title: Second-trimester screening for trisomy-21 using prefrontal space ratio.
abstract: OBJECTIVE
  To investigate the potential value of prefrontal space ratio (PFSR) in second-trimester screening for trisomy-21.
  
  
  METHODS
  A retrospective study utilizing stored midsagittal two-dimensional images of fetal profiles in 240 euploid and 45 trisomy-21 pregnancies at 16(+0)-23(+6) weeks' gestation. The vertical distance between the leading edge of the skull and that of the skin (D1) and the distance between the skull and the mandibulo-maxillary line (D2) were measured and the D1:D2 ratio (PFSR) was calculated. In euploid pregnancies, regression analysis was used to determine the association between D1, D2 and PFSR with gestational age (GA). D1 and D2 were expressed as delta (Δ) values with gestational age. ΔD1, ΔD2 and PFSR in cases and controls were compared.
  
  
  RESULTS
  In trisomy-21, compared to controls, ΔD1 was increased (1.417 vs. 0.000 mm, p < 0.0001), ΔD2 was decreased (-0.842 vs. 0.000 mm, p = 0.003) and PFSR was increased (0.753 vs. 0.463, p < 0.0001). At a false-positive rate of 5%, the detection rates in screening by ΔD1, ΔD2 and PSFR were 80.0% (95% CI 65.4-90.4), 46.7% (95% CI 31.7-62.1) and 100.0% (95% CI 92.1-100.0), respectively.
  
  
  CONCLUSIONS
  The PFSR is an effective marker in second-trimester screening for trisomy-21.
authors.affiliation: Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK.
authors.forename: Petya
authors.initials: P
authors.lastname: Chaveeva
authors.forename: Maria
authors.initials: M
authors.lastname: Agathokleous
authors.forename: Leona C Y
authors.initials: LC
authors.lastname: Poon
authors.forename: Desislava
authors.initials: D
authors.lastname: Markova
authors.forename: Kypros H
authors.initials: KH
authors.lastname: Nicolaides
mesh_terms: D000293:Adolescent; D000328:Adult; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000235:genetics; D005260:Female; D005819:Genetic Markers; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D008403:Mass Screening / Q000379:methods; D008875:Middle Aged; D015588:Observer Variation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000235:genetics; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal / Q000379:methods; D055815:Young Adult
chemical_list: D005819:Genetic Markers