Nasal bone in first trimester

(A) Nasal bone: Mid-sagittal view demonstrating the nasal bone of a fetus at 12 weeks. Note that the nasal bone is thicker and more echogenic than the overlying skin, making an "=" sign.
(B) Absent nasal bone: Midsagittal scan demonstrating an absent nasal bone and a thickened nuchal translucency (3.3 mm) of a fetus at 13 weeks with trisomy 21. Note that the skin edge is echogenic and could be mistaken as the nasal bone. Credentialing is required to perform this assessment reliably.
(C) Nasal bridge: Midsagittal view demonstrating the nasal bridge of a fetus at 12 weeks. Note that the nasal bone is thinner and less echogenic than the overlying skin edge: This should be considered "absent" and was the only abnormal finding in this fetus with trisomy 21.