ABSTRACT
The association of nasal bone hypoplasia and trisomy 21 is now well established. There are ultrasound studies in low-risk and high-risk populations, and also histopathological studies in fetuses with Down syndrome, which have consistently confirmed this association. Some 50-60% of fetuses with Down syndrome will have absent nasal bones at 11-14 weeks on ultrasound scanning. However, nasal bones may be absent in a small proportion of chromosomally normal fetuses as well. The background prevalence of absent nasal bones in normal fetuses is dependent on the parent’s ethnicity and facial structure.
