title: Second trimester ultrasound prenasal thickness combined with nasal bone length: a new method of Down syndrome screening.
abstract: OBJECTIVE
  To evaluate ultrasound prenasal thickness (PT) as a way of enhancing the Down syndrome (DS) screening performance of second-trimester nasal bone (NB) length measurement.
  
  
  METHODS
  Twenty-one DS and 500 normal fetuses were scanned at 14-27 weeks' gestation. The affected karyotype was known to the person performing the scan. Both PT and NB were measured in a mid-sagittal position and results were expressed in multiples of the normal gestation-specific median (MoM). Gaussian modelling was used to predict the performance of routine screening.
  
  
  RESULTS
  Among DS fetuses, the PT median was 1.35 MoM, a highly statistically significant increase compared with the unaffected pregnancies (p < 0.0001, Wilcoxon Rank Sum Test, two-tailed). The NB median was 0.87 MoM (p < 0.0005) and the ratio PT/NB median was 1.51 MoM (p < 0.0001). In the normal fetuses, the two markers were positively correlated (0.25, p < 0.0001), whereas in the DS fetuses there was a non-significant negative correlation (-0.24, p = 0.33). For a 5% false-positive rate, the model predicted detection rate was 70% for PT and NB compared with 43% for NB alone.
  
  
  CONCLUSIONS
  In the second trimester, PT is increased on average in DS fetuses. Combining PT and NB measurement could yield a higher screening detection rate than NB alone. Confirmation of our findings in a series of women scanned before the karyotype was known is needed before the method can be clinically implemented.
authors.affiliation: Department of Obstetrics and Gynecology, Assaf Harofe Medical Center, affiliated to the Sackler Faculty of Medicine, Tel Aviv University, Israel. intposgr@post.tau.ac.il
authors.forename: Ron
authors.initials: R
authors.lastname: Maymon
authors.forename: Orna
authors.initials: O
authors.lastname: Levinsohn-Tavor
authors.forename: Howard
authors.initials: H
authors.lastname: Cuckle
authors.forename: Yosef
authors.initials: Y
authors.lastname: Tovbin
authors.forename: Eli
authors.initials: E
authors.lastname: Dreazen
authors.forename: Yifat
authors.initials: Y
authors.lastname: Wiener
authors.forename: Arie
authors.initials: A
authors.lastname: Herman
mesh_terms: D004314:Down Syndrome / Q000175:diagnosis*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D009295:Nasal Bone / Q000000981:diagnostic imaging / Q000196:embryology*; D009666:Nose / Q000000981:diagnostic imaging / Q000196:embryology*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D012044:Regression Analysis; D016216:Ultrasonography, Prenatal / Q000379:methods*