Nuchal Translucency Scan
Nuchal translucency is a collection of fluid under the skin at the back of a baby's neck. The nuchal translucency scan measures the thickness of this fluid to assess the risk of Down's syndrome or chromosomal abnormalities.
A nuchal translucency scan can only indicate the level of risk of your baby having Down's syndrome. To get a definitive diagnosis, a test such as CVS or amniocentesis is necessary.
The NT scan is usually performed between 11.0 and 13.6 weeks of pregnancy.
The various conditions associated with increased nuchal translucency suggests that there may not be a single underlying mechanism for the collection of fluid in the skin of the fetal neck. Possible mechanisms include:
- Cardiac failure in association with abnormalities of the heart and great arteries;
- Venous congestion in the head and neck, due to constriction of the fetal body in amnion rupture sequence or superior mediastinal compression found in diaphragmatic hernia or the narrow chest in skeletal dysplasia;
- Altered composition of the extracellular matrix;
- Abnormal or delayed development of the lymphatic system;
- Failure of lymphatic drainage due to impaired fetal movements in various neuromuscular disorders;
- Fetal anemia or hypoproteinemia;
- Congenital infection, acting through anemia or cardiac dysfunction.