label: Absent fetal nasal bone
label_lc: absent fetal nasal bone
description: "The nasal bone is considered absent when it is not visualized on a midsagittal view of the profile. In the second trimester, a true midsagittal view of the fetal profile is obtained and magnified to fill the majority of the image space. The nasal bone appears as an echogenic linear structure below the skin edge. The optimal angle of insonation is 45 degrees to the longitudinal axis of the fetal nasal bone. If the angle of insonation is 0 or 180 degrees, the nasal bone may appear artificially absent. The presence or absence of the nasal bone may be determined at the time of the 11- to 14-week ultrasound examination and used as part of the risk assessment for aneuploidy."