Nuchal translucency test. Coloured ultrasound scan of the head and neck of a 13 week foetus taken during a nuchal fold translucency test for Down's syndrome. The nuchal fold (red) is a collection of fluid between two layers of skin at the back of the foetus' neck. It is present in all foetuses, but is more pronounced and opaque in those at a higher risk of Down's syndrome. This foetus has a narrow and clear nuchal fold, indicating that it has a low risk. This diagnosis is further confirmed by the normal profile of the face and presence of a nasal bone. An ultrasound scan is a non-invasive procedure that poses no risk to the foetus. If it is found that the foetus is at a higher risk of Down's syndrome further invasive tests can be taken to confirm the diagnosis.