Nuchal translucency scan: the screening test for Down's, Edwards' and Patau's syndromes
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Your nuchal translucency (NT) scan takes place at the end of your first trimester to help assess your unborn baby's chances of being born with Down's syndrome, Edwards' syndrome or Patau's syndrome. Here's what it involves ...
What exactly is the nuchal translucency scan?
The nuchal translucency scan – or nuchal scan for short – is one of the routine prenatal ultrasound scans that you'll have during your pregnancy.
This particular one looks for a collection of fluid under the skin at the back of your baby's neck. This is called nuchal translucency.
All babies have some fluid here but an increased amount can be a sign that they have chromosome abnormalities present in Down's syndrome and other rarer conditions, Edwards' syndrome and Patau's syndrome.
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Therefore the nuchal scan is widely used as a non-invasive screening test for these conditions.
Having the scan alone is around 77% effective but, combined with a blood test, it becomes 90% effective, according to the NHS.
This is why the nuchal scan is sometimes referred to as the 'combined screening test' or 'nuchal translucency (NT) screening test.'
The combined test takes into account your blood test result, your nuchal measurement and your age and calculates your chances of having a baby with Down's, Edwards' or Patau's syndromes.
When will I have my nuchal translucency scan?
Your nuchal scan takes place towards the end of your first trimester (somewhere between 11 and 14 weeks).
It'll sometimes take place at your dating scan appointment but if you happen to be earlier than 11 weeks, you'll have to come back for it a week or two later.
And, if you're later than 14 weeks then you'll require a separate blood test instead.
This is because the nuchal scan needs to take a specific measurement when the baby is a specific age and the fluid is still visible.
What does the nuchal translucency scan involve?
You'll receive a letter telling you when to come in for your scan.
You'll need to have a fairly full bladder (although not too full as the sonographer doing the scan will push down on your bladder!) This helps get a clearer view of what's going on inside you.
Similar to other pregnancy scans, you'll lie down and won't need to undress. Just adjust your clothes so that you can see your abdomen.
Then the sonographer will apply some cold gel to your stomach to help the scanning head glide over your skin and get a good image.
Once the skin fold has been detected, measurements will be taken on screen, then printed out as a graph for your obstetrician to consider.
If you've agreed to have the combined test, you'll have a blood test at the same appointment.
Nuchal translucency scan: getting your results
Your results will be sent out by post within a couple of weeks.
They'll tell you whether you have:
- a high chance (higher than 1 in 150) of having a baby with Down's syndrome
- a low chance (less than 1 in 150) of having a baby with Down's syndrome.
They'll also tell you whether you have:
- a high chance (higher than 1 in 150) of having a baby with for Edwards’ and Patau’s syndromes
- a low chance (less than 1 in 150) of having a baby with Edwards’ and Patau’s syndromes.
Do I have to have the nuchal translucency scan?
No, you don't.
However, as the scan is non-invasive and does absolutely no harm to your pregnancy or your baby, most women will choose to have it done.
According to the NHS, 'over 95 out of 100 (95%) screening test results will be lower chance'.
So, as this is most likely to be the outcome, it could offer huge peace of mind for the rest of your pregnancy.
If your results come back saying there's a high chance, you'll at least be armed with plenty of support and help with any further tests and decisions to make.
It's always good to be prepared, after all.
A high chance of Down's syndrome: what do I do next?
If your nuchal screening test result comes back as having a high chance, remember it's still only a likelihood – not a guaranteed diagnosis.
To get further clarity, you'll be offered some further diagnostic tests (see below).
You'll also be given support and advice about the particular syndrome.
For instance, a lot more is known about Down's syndrome than in previous generations. These days there's lots of support in place ready to help parents.
For help and advice with your test results and what to do next, you can always contact these organisations:
- Antenatal Results and Choices (ARC)
- Down's Syndrome Association
- Positive about Down syndrome
- SOFT UK (the charity for Edward’s and Patau’s syndrome).
What's Down's syndrome?
According to the NHS:
'In Down’s syndrome there is an extra copy of chromosome 21 in each cell. It affects about 1 in every 1,000 births.'
Generally speaking it causes learning disabilities and communication difficulties and is often recognised by specific facial features such as almond-shaped eyes and distinctive facial features.
More severe cases of Down's syndrome can cause health problems such as hearing, vision, heart and digestive issues.
However, with good support and healthcare in place, your child can have a good quality of life these days.
What are Edwards' and Patau's syndromes?
According to the NHS:
- Babies with Edwards’ syndrome have an extra copy of chromosome 18 in each cell. It affects about 3 of every 10,000 births.
- Babies with Patau’s syndrome have an extra copy of chromosome 13 in each cell. It affects about 2 of every 10,000 births.
Although both these syndromes are much rarer than Down's syndrome, they are also much more serious.
Both can cause heart problems amongst other developmental problems and can even be fatal, according to the NHS, sadly:
'Most babies with Edwards’ or Patau’s syndromes will die before they are born, be stillborn or die shortly after birth. Some babies may survive to adulthood but this is rare.
'All babies born with Edwards’ and Patau’s syndromes will have a wide range of problems, which are usually extremely serious – these may include major brain abnormalities.'
You'll be offered support and counselling to help with your decision. This could include further testing and unfortunately, the possibility of a termination.
For support and help with your test results, chat to other mums in our forum.
You can always contact the organisations listed above, too.
Will further tests harm my baby?
To find out for certain whether or not the baby has Down’s, Edwards’ or Patau’s syndromes, you'll be offered one of two diagnostic tests depending on how many weeks pregnant you are. These are:
- CVS (chorionic villus sampling) – this has to be performed when you're between 11-14 weeks pregnant
- Amniocentesis – this has to be performed after you're 15 weeks pregnant
Unfortunately, these tests are invasive (requiring a needle to pass through your abdomen and collect either a sample of the placenta or fluid surrounding the baby) and there are risks attached.
The NHS advises patients as follows:
'About 1 to 2 in every 200 (0.5% to 1%) diagnostic tests result in a miscarriage. It is up to you whether or not to have the further test.'
A non-invasive prenatal test (NIPT) has been developed but is yet to be made available on the NHS.
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