Ultrasonographic evaluation of fetal nasal bone in a low‐risk population at 11–13 + 6 gestational weeks

Objective To evaluate the utility of determining the presence/absence of nasal bone in a low‐risk fetal population. Methods Prospective study of the presence/absence of nasal bone among 1800 consecutive unselected fetuses, with complete follow‐up of results. Results An adequate sonographic evaluation of nasal bone was obtained in 1682 (93.44%) of the fetuses. Nasal bone was considered absent in 19 (1.06%) of 1790 fetuses with a normal karyotype and in 2 (28.57%) of the seven recorded cases of Down syndrome (DS). The overall first‐trimester sensitivity for DS to the absence of nasal bone was two of the six cases (33.3%) and the false‐positive rate was 1.13%. The positive predictive value for DS of the absence of nasal bone was 2/21 (9.52%). Conclusions In a low‐risk population, the evaluation of the presence/absence of nasal bone in DS screening during the first trimester has a low sensitivity. First‐trimester assessment of the nasal bone in population screening may play a lesser role than in the re‐evaluation of high‐risk pregnancies. Copyright © 2006 John Wiley & Sons, Ltd.