During your 12-week scan, measurements will also be taken to establish the amount of fluid under the skin at the back of the baby's neck – the nuchal translucency.
This is used to establish whether there is an increased risk of the baby having Down's syndrome. Less than 3mm of fluid behind the neck indicates a low risk, and this will be the result for 95 per cent of women. If the measurement is between 4 and 7mm, further investigations will be offered. The nuchal scan gives an indication of the possibility of Down's syndrome but is by no means conclusive and relies on further diagnostic tests, such as amniocentesis, to confirm the diagnosis.
Nuchal Translucency Scan Photos
Click to Photo for Next Images of Nuchal Translucency Scan
This 3D ultrasound scan is of a 12-week-old fetus in the uterus. Its head is on the right, and the developing facial features can be seen.
The sonographer sweeps a hand-held transducer across your abdomen to pick up sound waves from fetal structures.
The small depth of fluid behind the neck indicates a low risk of Down's syndrome.
A larger depth of fluid puts the fetus at a higher risk of Down's syndrome.