About the Combined Test (Nuchal Translucency Scan)
This is a screening test based on an ultrasound scan and blood test at about 12 weeks (11+3 to 13+6 weeks) to assess the probability of Down Syndrome, Edward Syndrome and Patau Syndrome in the baby.
How does the test work?
By measuring the thickness of tissue fluid that lies under the skin at the back of the baby’s neck (the Nuchal Translucency), a computer programme can convert this measurement plus the length of the baby and the mother’s age into a single probability for Down Syndrome, Edward Syndrome and Patau Syndrome. As it is based on the appearance of an individual baby, the technique can also be used in multiple pregnancies to give a probability for each baby.
Why do I also have a blood test?
The test has a detection rate of 80% based just on the scan. This increases to around 85% in single pregnancies if blood markers (PAPP-A and free B-hCG) are also measured in a sample of blood taken from your arm at the time of the scan. Results based on scan are available on the day and blood tests results are usually available within a few days.
If the probability result is more than 1:150 then further testing like CVS, Amniocentesis or non-invasive prenatal testing (NIPT) should be considered.
Does the NHS offer this test?
Yes, the NHS offers the combined test and offers further testing such as NIPT following a high probability result.