Guidelines for Measuring NT
The fetal crown-rump length should be between 45 and 84mm.
A good sagittal section of the fetus must be obtained, with the fetus horizontal on the screen.
The fetus should be in a neutral position, , with the head in line with the spine, not hyper-extended or flexed.
The fetus should be magnified so that the head to upper thorax occupy the whole of the image.
The widest part of translucency must be measured.
Measurements should be taken with the inner border of the horizontal line of the calipers placed ON the line that defines the nuchal translucency thickness - the crossbar of the caliper should be such that it hardly visible as it merges with the white line of the border, not in the nuchal fluid.
Turning down the gain can reduce any fuzziness to the line. Otherwise the callipers should be placed on the sharpest region of the border, not on the fuzzy edge. Do not use harmonics or post-zoom magnification – both accentuate the fuzziness.
Care must be taken to distinguish between fetal skin and amnion.
During the scan more than one measurement must be taken and the maximum one that meets all the above criteria should be recorded in the database. It is good practice to retain at least one image for your patient records.