Nasal bone assessment in prenatal screening for trisomy 21.

A small nose is a common facial feature of individuals with trisomy 21. Evidence based on radiologic, histomorphologic, and sonographic studies shows that nasal bone abnormalities are significantly more common in trisomy 21 fetuses than in euploid fetuses. These abnormalities, which include both nasal bone absence and short nasal bone length, can be detected by prenatal ultrasound. In this article we review the evidence and discuss the potential value of assessment of the fetal nasal bone in screening for trisomy 21.