Nasal bone

At 11-13 weeks the nasal bone is considered to be absent in:

• Euploid fetuses 1-3%
• Fetuses with trisomy 21 60%
• Fetuses with trisomy 18 50%
• Fetuses with trisomy 13 40%

Absence of the nasal bone is more common if:

• The gestation is 11 than 13 weeks.
• The fetal nuchal translucency is high.
• The mother is Black.