Nuchal Translucency Imaging

This illustrates the anatomy of a first-trimester fetus using optical lighting, an MRI scan, and ultrasound. The nuchal translucency is located posterior to the back of the skull and neck. It is translucent, and contains fluid.


 This represents three imaging modalities that identify early fetal development. The fetus on the left is an actual photo at 12 weeks. The fetus in the middle is from an MRI study and the fetus on the right is an ultrasound. The blue areas behind the neck represent the nuchal translucency that is measured during the first-trimester scan when evaluating the fetus for Down syndrome and other birth defects.

Measurement of the Nuchal Translucency

There are several steps that hat the physician should consider when performing the ultrasound examination during the first trimester. They are as follows:

1. The magnification of the image should be as large as possible and the calipers able to produce 0.1 mm changes in the measurement.

2. The nuchal translucency measurement should be obtained between 11 weeks and 13 weeks six days which would be equivalent to a crown-rump length between 45 and 84 millimeters.

 Crown-Rump Length Measurement

3. A sagittal section of the fetus should be obtained, in a neutral position.

4. The widest part of the translucency should be measured.

 The widest nuchal translucency measurement should be made, as indicated in this example by the green arrows.

5. Measurements should be taken with the horizontal lines placed on the lines that define the nuchal translucency thickness

 This image compares the actual specimen with the ultrasound measurement of the nuchal translucency.


Example of an Abnormal Nuchal Translucency Measurement

 The fetus on the left has a normal nuchal translucency measurement (green line). The fetus on the right has an increased nuchal translucency measurement (green line)