Second trimester ultrasound prenasal thickness combined with nasal bone length: A new method of Down syndrome screening

Ron Maymon*, Orna Levinsohn-Tavor, Howard Cuckle, Yosef Tovbin, Eli Dreazen, Yifat Wiener, Arie Herman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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. Conclusion: 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.

Original languageEnglish
Pages (from-to)906-911
Number of pages6
JournalPrenatal Diagnosis
Issue number10
StatePublished - Oct 2005


  • Down syndrome
  • Nasal bone
  • Prenasal thickness
  • Screening
  • Ultrasound


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