What is nuchal translucency (NT)?
Every unborn baby has some fluid under the skin at the back of their neck. This fluid is called nuchal translucency (NT).
You can see this fluid on the ultrasound scan early on in your pregnancy. It is part of a baby’s normal development in the womb but, if your baby has more fluid than usual, it can sometimes be a sign that they have a health problem. This may be a physical problem (for example, a heart
problem) or chromosome condition (for example, Down’s syndrome).
If we have suggested you read this information, it is because your baby’s NT is 3.5mm or more.
It is important to remember that many babies who have more fluid than usual at the back of their neck at an early scan can be both healthy and well.
We will also offer you an appointment with a specialist or midwife to discuss what this might mean for you and your baby.
Why do you measure NT?
All pregnant women in England are offered a screening test to give them information on the chance of their baby having a chromosomal condition.
We measure the NT as part of the ‘combined’ screening test for Down’s syndrome, Edwards Syndrome and Patau’s Syndrome. This test combines the result of a blood test taken from the mother with the measurement of the NT from the baby seen on the scan.
You may have chosen not to have your baby screened for Down’s syndrome, Edwards Syndrome or Patau’s Syndrome. However, because an increased NT maybe associated with physical problems and other chromosome conditions in your baby, the sonographer undertaking the scan has an obligation to tell you if they see an increased measurement of more than 3.5mm of fluid at the back of your baby’s neck.
What is a normal NT measurement?
We cannot give you a normal figure, because the NT usually grows in proportion with your baby. This means that the measurement depends on how many weeks pregnant you are when you have your scan.
However, we do know that if early in your pregnancy the NT is 3.5mm or more, there is a higher chance that your baby may have a physical problem or chromosome condition.
What happens now I know my baby has an increased NT measurement?
You will be given an appointment with a specialist or midwife regarding different diagnostic testing that is available for you and your baby.
If you would like diagnostic testing we will send a referral over to our tertiary testing unit, which in Sheffield fetal medicine or in Scunthorpe with our trusts fetal medicine obstetrician.
A member of their team will contact you to make an offer of a diagnostic test such as Chorionic Villus Sampling (CVS) or Amniocentesis (Amnio) within three to five working days of receiving a raised NT result. At this appointment you will see a specialist from the fetal medicine team who will perform your diagnostic testing.
Although this can be worrying, it is important to remember that many babies whose NT measurement is 3.5mm or more are healthy. An increased NT does not mean there is definitely a problem.
Definitions of terms
We use medical terminology every day and, while we do our best to explain any medical terms and avoid using jargon when speaking to you, we appreciate it can be a lot to take in. To help, we have put together this guide.
If you ever have questions or don’t understand something we have said, please just ask.
Nuchal Translucency (NT) scan: You will have an NT scan when you are between 11+2 weeks and 14+1 weeks pregnant. This measures the thickness of the fluid at the back of your baby’s neck. An increased amount of fluid may show that your baby is at an increased risk of a physical problem or chromosome condition.
By combining your age and how many weeks pregnant you are with information from the scan, the lab will calculate your chance factor. If you have a one in 150 chance, or higher, you will be offered a diagnostic test, such as a chorionic villus sampling (CVS) test.
Chorionic villus sampling (CVS): CVS is a test carried out during pregnancy which involves removing tissue from the placenta and is used to detect chromosomal abnormalities such as Down’s syndrome or conditions such as sickle-cell diseases. It can also detect certain other genetic conditions.
CVS is also known as a diagnostic test because it gives you a diagnosis. For example, it tells you that your baby does or does not have Down’s syndrome.
There is a miscarriage risk associated with CVS which is one in every 100 women (1%).
Amniocentesis: Amniocentesis is carried out from the 15th week of pregnancy and involves removing approximately 20mls of amniotic fluid via a fine needle through the abdomen.
This will be performed at either Scunthorpe General Hospital or Sheffield fetal medicine unit (this decision is purely down to patient choice).
Amniocentesis is a diagnostic test because, just like CVS, it gives you a diagnosis. For example, it tells you that your baby does or does not have Down’s Syndrome.
There is a miscarriage risk associated with Amniocentesis which is one in every 100 women (1%).
Chromosome condition: Chromosomes are structures which are found in the nucleus of a cell, and are made up of DNA and proteins.
Normally humans have 46 chromosomes in each cell, 23 from each parent. Of these, 22 are autosomes and one is a sex chromosome. A chromosome condition is when there is a change in the number or arrangement of the normal 23 pairs of chromosomes which has an effect on
the health of the baby.
Down’s syndrome (Trisomy 21 or T21): Down’s syndrome is a disorder which affects all population groups and is caused by having an extra chromosome. People with Down’s syndrome have three copies of chromosome number 21 instead of two.
People with the condition usually have:
- Low muscle tone
- A flatter face
- Eyes which slant upward
- Small ears
- An unusually wide neck
- A deep crease across the palm of their hand
Some people may also have heart problems or sight problems or may develop Alzheimer’s disease. Although people with Down’s syndrome have learning difficulties, these vary in how severe they are.
Edward’s syndrome (T18): Edward’s syndrome is a disorder caused by an extra copy of Chromosome 18. In effects on average three in 10,000 births.
Edward’s Syndrome is a serious condition and affected babies can result in a range of severe medical problems including:
- A low birth weight
- A small head (microcephaly)
- Severe learning difficulties
- Malformations of the heart
- Malformations of the kidneys
- Clenched fists and malformed feet
- Feeding and breathing problems
- Cleft lip and/ or cleft palate
Sadly, most babies with Edward’s syndrome die before the end of the pregnancy or are stillborn. Of the babies with Edward’s syndrome that are born alive, about half survive the first month of life and less than one in ten (10%) live longer than a year.
Patau’s syndrome (T13): Patau’s syndrome is a condition caused by an extra copy of Chromosome 13. Patau’s syndrome is a serious condition and affected babies can have a range of severe medical problems Including:
- A low birth weight
- Holoprosencephaly (where the brain does not divide into two halves)
- Cleft lip and/ or palate
- An abnormally small eye or eyes (microphthalmia)
- The absence of one or both eyes (Anophthalmia)
- A small head (microcephaly)
Unfortunately there is no specific treatment for Patau’s syndrome and, for the small number of babies who survive the first few days of live, their care will depend on their specific needs.
Specialist: A specialist could include an Obstetrician, a Fetal Medicine Nurse, an Antenatal Clinic Midwife, or a Specialist Sonographer.
Where can I get more information?
If you have any questions while you are waiting for your appointment with the specialist team, please contact the screening team:
Deputy Screening Coordinator – 03033 303019
You may also find it helpful to contact the following charities and support groups. We also understand that at a time like this, it is natural to want as much information as possible and you may search online. However, please bear in mind that not all information on the internet is accurate or reputable.
We recommend the following sites:
Antenatal Results and Choices (ARC): Antenatal results and choices (ARC) provides impartial information and individual support to parents while they are going through antenatal screening or when their unborn baby has been diagnosed with an abnormality.
Helpline: 0207 6310285
Address: 73 Charlotte Street, London, W1T 4PN
Down’s Syndrome Association: The Down’s Syndrome Association (DSA) is the only charity in the UK dealing with all aspects of Down’s syndrome. Its aim is to help people who have Down’s syndrome live full and rewarding lives.
Helpline: +44 (0)333 1212 300
Address: Langdon Down Centre, 2a Langdon Park, Teddington, Middlesex,
Date of Issue: June, 2021
Review Period: June, 2024