About the Nuchal Scan
Why have a Nuchal scan with combined blood tests?
Although most babies are healthy, chromosomal abnormalities such as Down’s Syndrome occur in approximately 1 in 600 births. Down’s syndrome is more common in older mothers, but can occur at any age. ‘Screening tests’ such as the Nuchal scan are available to calculate the chances of an individual baby being affected by Down’s syndrome. It is important to understand that this will not tell you definitely whether your baby has this condition, but it will give you the information to help you to decide if you need to have a diagnostic test (amniocentesis or chorionic villus sampling (CVS)), which will tell you for sure.
What is a Nuchal scan with combined blood tests?
- The Nuchal scan is a detailed scan between 11 and 13 weeks that measures the thickness at the back of the baby’s neck down to a tenth of a millimetre. We know that babies with thicker measurements are more likely to have problems. Therefore, using this measurement combined with both your age and the size of the baby, we can work out the risks for Down’s syndrome, and some other chromosomal problems.
- The blood tests check hormone levels. These can be altered in the blood of mothers with a baby with Down’s Syndrome and other chromosomal problems.
When we know both the Nuchal scan measurements and the blood hormone levels, we can calculate the actual risk of Down’s syndrome, using also your date of birth. This makes the best screening test in early pregnancy.
How accurate is this test?
Simply using Nuchal translucency alone will identify about 80% of Down syndrome babies, but research shows that if you combine the Nuchal scan with an early blood test, this detection rate goes up to 90%. For this reason, we now only perform the Nuchal scan if blood tests are used as well.
What does the Nuchal scan involve?
The scan usually takes about 20 minutes, although it can take much longer if the baby is in a difficult position. You do not need to have a full bladder. If you are uncertain of the date of your last menstrual period, it is recommended that you have a dating scan prior to the Nuchal scan.
Your blood can be taken at any time from 9 to 12 weeks. Preferably, this should be nearer 9 weeks, but if the blood is sent 48 hours before the scan we will usually have the result in time. Blood can be taken on Level 1 of the Women’s Centre at the John Radcliffe; or it can be taken by your midwife or at your doctor’s surgery if you have checked with them first. Once your blood has been taken, you should put it in the stamped addressed pack and post it the same day as it is taken (more detailed instructions are given with each pack). We advise that blood is not taken or sent on a Thursday or Friday because of postal problems. We ask that you do not contact the office to ensure the blood result has arrived: we will normally contact you.
What else does the scan do?
As well as screening for chromosomal problems and detecting some structural problems, the Nuchal scan will accurately date the pregnancy, detect twins, and allows you to see your baby in detail.