A nuchal scan or nuchal translucency (NT) scan/procedure is a sonographic prenatal screening scan (ultrasound) to detect chromosomal abnormalities in a fetus, though altered extracellular matrix composition and limited lymphatic drainage can also be detected.

Since chromosomal abnormalities can result in impaired cardiovascular development, a nuchal translucency scan is used as a screening, rather than diagnostic, tool for conditions such as Down syndrome, Patau’s syndrome and Edwards Syndrome and non-genetic Body-stalk anomaly

There are two distinct measurements: the size of the nuchal translucency and the thickness of the nuchal fold. Nuchal translucency size is typically assessed at the end of the first trimester, between 11 weeks 3 days and 13 weeks 6 days of pregnancy.[3] Nuchal fold thickness is measured towards the end of the second trimester. As nuchal translucency size increases, the chances of a chromosomal abnormality and mortality increase; 65% of the largest translucencies (>6.5mm) are due to chromosomal abnormality, while fatality is 19% at this size. A nuchal scan may also help confirm both the accuracy of the pregnancy dates and the fetal viability

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