The nuchal fold scan (sometimes known as the ‘nuchal translucency scan’) is performed at the end of your first trimester of pregnancy between weeks 11 and 14, with the most optimal time being the 12th week. At this time, you’re also offered a combination of blood tests for more information about the risk of chromosomal abnormalities.
Chromosomes make up the genetic code for how a baby will develop, ensuring certain traits and characteristics pass from parent to child. Sometimes too few, or too many, chromosomes are passed on and this is when developmental abnormalities such as Down’s syndrome occur. Down’s syndrome (less frequently known as Trisomy 21) is the result of having one extra chromosome in all cells of the body.
This article on the nuchal fold scan is written by Jackie Griffiths, a freelance journalist who writes health, medical, biological, and pharmaceutical articles for national and international journals, newsletters and web sites.
Why do you have a nuchal fold scan?
The nuchal fold scan is an ultrasound test that checks the amount of fluid beneath the skin of the baby’s neck. Babies with Down’s syndrome (a chromosomal disorder) often have a thicker layer than babies who do not have Down’s syndrome. The sonographer will also look to see if the baby’s nasal bone is present or shortened as this can also be a marker for foetal abnormalities.
What do the blood tests tell you?
At your Nuchal fold scan, the blood tests measure the amount of HCG and PAPP-A protein in your blood. High levels of HCG twinned with low levels of PAPP-A can mean the baby has a chromosomal abnormality such as Down’s syndrome.
Although the nuchal fold scan can identify approximately 75% of babies with Down’s syndrome, around 5% of normal babies also receive high-risk markers.
What can you see at the scan?
Although it’s possible to see the heartbeat and measure the foetus at earlier scans, this is the first chance for you and the sonographer to see the baby in greater detail. You should be able to see the whole body of the baby - the head, arms, legs, hands and feet, and the sonographer will be able to examine the placenta, amniotic fluid, and umbilical cord. You may also be able to see the baby make movements and wave its arms and legs about. You may be offered pictures printed out from the scan that you can take home with you.
If there are any major abnormalities in your growing baby the sonographer will usually be able to identify them at the nuchal fold scan.
How reliable is a scan?
In every 1,000 babies born in the UK, one will be affected by Down’s syndrome. From the nuchal fold scan alone about 75% of cases are correctly identified, but when combined with the blood test the success in predicting Down’s syndrome risk rises to about 90%.
What should I do if my risk is high?
Many women who receive a high-risk result at their nuchal fold scan go on to have healthy babies. However, the older the mother the greater the risk factor.
If your nuchal translucency scan identifies that your baby is at a high risk of having Down’s syndrome, other diagnostic tests are available that can tell you for sure. These tests are more invasive and carry about a 1% risk of miscarriage. A CVS (chorionic villous sample) test can be done at 12 weeks and or you can wait until week 16 and have an amniocentesis.