title: A model for second-trimester Down syndrome sonographic screening based on facial landmarks and digit length measurement.
abstract: OBJECTIVE
  To determine whether Down syndrome can be detected by combining measurements of fetal nasal bone (NB) length, prenasal thickness (PT) and digits 2 and 3 of the hand.
  
  
  METHODS
  Two hundred and fifty-four normal and 25 Down-syndrome fetuses were scanned between 15 and 33 weeks' gestation. Physicians performing the scans were not blinded to the fetal karyotype. Both PT and NB were measured in a mid-sagittal plane. For PT measurement calipers were placed between the frontonasal angle and the outer skin edge. Digits 2 and 3 of one hand were also measured. The results (except for PT/NB ratio) were expressed in multiples of the normal gestation-specific median (MoM). A logistic regression model was used to estimate the odds of the fetus having Down syndrome given different combinations of NB, PT, PT/NB ratio, and digits 2 and 3 measurements. The odds were used to calculate the risk of Down syndrome for each pregnant woman from her age and measurements.
  
  
  RESULTS
  The median PT MoM for unaffected fetuses and Down-syndrome fetuses was 1.12 vs. 1.35 (P < 0.0001). The median NB MoM for unaffected and Down-syndrome fetuses was 1.03 vs. 0.81 (P < 0.001) and the PT/NB ratio MoM for unaffected and Down-syndrome fetuses was 0.63 vs. 0.96 (P < 0.001). The respective median MoM values for digits 2 and 3 of the Down-syndrome fetuses were significantly smaller (0.81 vs. 0.93 and 0.89 vs. 0.95, respectively, P = 0.003). Only the PT/NB ratio and digit 2 were finally included in the logistic regression equation. Using a 1 in 200 risk cut-off, the observed sensitivity and false-positive rate were 76% and 6.7%, respectively.
  
  
  CONCLUSIONS
  Combining the PT/NB ratio and digit 2 measurements yielded a promising screening detection rate. Confirmation of our findings in a prospective study is needed before the method can be used clinically.
authors.affiliation: Department of Obstetrics and Gynecology, Assaf Harofe Medical Center, Affiliated to The Sackler Faculty of Medicine, Tel Aviv University, Zerifin, Israel. intposgr@post.tau.ac.il
authors.forename: R
authors.initials: R
authors.lastname: Maymon
authors.forename: F
authors.initials: F
authors.lastname: Ushakov
authors.forename: D
authors.initials: D
authors.lastname: Waisman
authors.forename: H
authors.initials: H
authors.lastname: Cuckle
authors.forename: Y
authors.initials: Y
authors.lastname: Tovbin
authors.forename: A
authors.initials: A
authors.lastname: Herman
mesh_terms: D000328:Adult; D001699:Biometry; D003430:Cross-Sectional Studies; D004314:Down Syndrome / Q000000981:diagnostic imaging*; D005260:Female; D005385:Fingers / Q000000981:diagnostic imaging / Q000196:embryology*; D005865:Gestational Age; D006801:Humans; D009295:Nasal Bone / Q000000981:diagnostic imaging / Q000196:embryology*; D015588:Observer Variation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011446:Prospective Studies; D014463:Ultrasonography