Send to

Choose Destination
Prenat Diagn. 2005 Oct;25(10):906-11.

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

Author information

Department of Obstetrics and Gynecology, Assaf Harofe Medical Center, affiliated to the Sackler Faculty of Medicine, Tel Aviv University, Israel.



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.


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.


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.


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.

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Wiley
Loading ...
Support Center