Nasal bone and facial angle

For assessment of the nasal bone it is necessary to obtain the profile view of the fetal face and the image should be big so that the head and upper thorax occupy the whole screen (as shown in the top video)

When these criteria are satisfied, three distinct lines should be seen at the level of the fetal nose:

• The top line represents the skin
• The bottom one, which is thicker and more bright than the overlying skin, represents the nasal bone
• A third line in front of the bone and at a higher level than the skin represents the tip of the nose

The nasal bone is considered to be present if it is more bright than the overlying skin and absent if it is either not visible (as shown in the bottom video) or its brightness is the same or less than that of the skin

At 11-13 weeks there is absence of the nasal bone in 1 to 3% of chromosomally normal fetuses and in 60% of fetuses with trisomy 21. However, the vast majority of fetuses with absent nasal bone are normal and have a normal pregnancy outcome