Birth Definitions

Nuchal Translucency Definition

Nuchal Translucency

Nuchal translucency is the degree of translucency of the fluid-filled subcutaneous gap on the back of the fetal neck, typically seen during the late first trimester and early second trimester (11 weeks 3 days to 13 weeks 6 days).

The degree of translucency of the gap indicates density. High translucency means higher density owing to the presence of fluid. This is determined during an ultrasound scan. A high NT reading indicates an increased chance that the baby has chromosomal abnormalities (Down Syndrome or Edwards Syndrome) or other problems. The cutoff point at which a risk is considered high depends on the clinic and the age of the mother.

Nuchal Translucency-1

Nuchal translucency is also sometimes called nuchal fold thickness but they should not be interchanged.

Nuchal Translucency vs. Nuchal Fold Thickness

Nuchal translucency is not to be confused with nuchal fold thickness as the latter refers to the thickness of the layer of skin and subcutaneous tissue that lies over the back of the baby’s neck. The nuchal fold normally becomes thicker during the second trimester as more fat accumulates but increased thickness is also a soft marker associated with fetal anomalies. Like nuchal translucency, nuchal fold thickness is also measured during an ultrasound scan but at the end of the second trimester when nuchal transparency is no longer detectable.

A high nuchal fold thickness does not always mean that the baby has an increased risk for aneuploidy. Sometimes it just means that there is more tissue at the back of the baby’s neck.

This image shows how often the term ‘Nuchal Translucency’ is used in relation to other, similar birth terms:

Nuchal Translucency-graph

Other related tests

Nuchal translucency (NT), and nuchal fold thickness measurement are combined with factors like maternal age, serum Free β-human chorionic gonadotropin (β-hCG), a raised AFP level, and results of other tests blood tests to provide a risk assessment for Down’s syndrome and other chromosomal abnormalities such as Edwards syndrome, Patau syndrome, and Turner syndrome.

Other blood tests that test for chromosomal abnormalities include the following:

  1. Prenatal diagnostic tests for Down syndrome: Chromosomal microarray analysis (CMA) and perinatal blood sampling
  2. Prenatal diagnostic tests for Edwards syndrome: CMA and chorionic villus sampling (CVS)
  3. Noninvasive prenatal testing (NIPT)
  4. Triple test or Quadruple test (Quad)

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