Nuchal Thickness

Nuchal Thickness Measurement
Tips, Tricks and Significance

Take Home Points

what is the importance of the nuchal thickness measurement

First, nuchal fold thickness measurement (typically performed between 16-20 weeks) must be differentiated from the nuchal translucency measurement done in the first trimester.
Unlike other "soft markers" for chromosome abnormalities such as echogenic intracardiac foci, mild pyelectasis and choroid plexus cysts, thickening of the nuchal fold is a much "harder soft marker."
A thickened nuchal fold increases the risk of Down's Syndrome by 17 times.
In our opinion, every fetus with true nuchal fold thickening should undergo chromosomal analysis.

What are the landmarks for measuring the nuchal fold (axial plane)

Pitfalls

Easy to spuriously increase the measurement
- Particularly if you scan with too much obliquity through the foramen magnum
The occipital bone is often shadowed out in this image
- This is due to the critical angle of reflection artifact

MID-LINE sagittal plane measurement

When the nuchal fold measures too thick in the axial plane or we are having trouble getting an accurate measurement, we always confirm the measurement in the mid-sagittal plane.
Measurement should be done it the very inferior aspect of the occipital bone, perpendicular to the bone.
The mid-sagittal plane also has a pitfall. The fetus should have it's neck in neutral position. if the neck is extended, it will spuriously increase the measurement.

WHAT IS Normal measurement FOR NUCHAL THICKNESS

Some use < 5 mm as the normal measurement up to 18 weeks and then < 6 mm from 18-29 weeks.
Some use nuchal thickness up to 22-24 weeks, but we don't do that
Some use < 5 mm as the normal measurement up to 18 weeks.

look vs. measurement

The overall appearance of the nuchal fold can also be very helpful. A bulging appearance is very suspicious for Down's syndrome as well