The nasal bones are paired small bones forming the bridge of the nose. On prenatal ultrasound during the second trimester, the nasal bone can be visualized and measured in a standardized view. An absent or hypoplastic nasal bone has been associated with increased risk of Down syndrome (Trisomy 21) and other chromosomal abnormalities. Measurement of nasal bone length is incorporated into some screening algorithms along with maternal serum markers and nuchal translucency measurement to assess chromosomal risk. However, isolated nasal bone hypoplasia or absence can occur in normal pregnancies, and this finding must be interpreted in the context of other ultrasound markers and maternal age.
Sonography Term