Nuchal fold thickness

Nuchal fold thickness is a parameter that is measured in a second-trimester scan (at ~18-22 weeks) and should not be confused with nuchal translucency (which is measured in the first trimester).

The proposed aetiology of increased nuchal thickness is the result of congenital heart disease and lymphatic obstruction.

As the pregnancy progresses, excess nuchal thickness or even cystic hygromas can resolve, especially toward the third trimester; however, the risk of karyotypic abnormalities is not reduced.

Nuchal fold thickness is measured on an axial section through the head at the level of the thalami, cavum septi pellucidi, and cerebellar hemispheres (i.e. in the same plane that is used to assess the posterior fossa structures). One calliper should be placed on the skin, and the other against the outer edge of the occipital bone.

A thick nuchal fold is often considered the most sensitive and most specific 2nd trimester marker for Down syndrome with false positive rates as low as 1% 1,3.

Nuchal fold thickness of >5-6 mm is considered abnormal:

  • nuchal thickness should not be measured after 20.6 weeks
  • NF >5 mm: sensitivity 15%, specificity 97%, PPV 8%, NPV 99% for trisomy 21 9
  • NF >6 mm: sensitivity 12%, specificity 99%, PPV 13%, NPV 99% for trisomy 21 9
Ultrasound - obstetric
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Article information

rID: 1743
Section: Gamuts
Synonyms or Alternate Spellings:
  • Nuchal thickness
  • Thickened nuchal fold
  • Thick nuchal fold
  • Nuchal thickening
  • Nuchal fold thickening

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