Nuchal translucency (NT) scan

What is nuchal translucency?

Nuchal translucency is a collection of fluid under the skin at the back of your baby's neck. It can be measured using ultrasound:
  • between 11 weeks and 13 weeks plus six days of pregnancy
  • or when your baby measures between 45mm (1.8in) and 84mm (3.3in)
All babies have some fluid at the back of their neck. But many babies with Down's syndrome have an increased amount (Snijders et al 1998: 351, 343-6).

Why might I have an NT scan?

A nuchal translucency (NT) scan is a screening test that assesses whether or not your baby is likely to have Down's syndrome.

A screening test can only estimate the risk of your baby having Down's, whereas a diagnostic test, such as CVS or amniocentesis, will tell you for sure. However, diagnostic tests do carry a small risk of miscarriage.

An NT scan can't tell you for certain whether or not your baby is affected. What it can do is help you to decide whether or not to have a diagnostic test.

How is the NT scan performed?

This ultrasound scan must take place at between 11 weeks and 13 weeks plus six days of pregnancy, or when your baby is between 45mm and 84mm.

Before this the scan is difficult to do because your baby is still so tiny. It would also be too early to combine it with your first trimester blood test.

After 14 weeks, any excess fluid may be absorbed by your baby's developing lymphatic system.

The scan is usually done through your tummy. However, a vaginal scan may be needed, as it gives better views, especially if your uterus (womb) tilts backwards, or if you are overweight. This is quite safe for you and your baby, and it shouldn't be too uncomfortable either.

To date your pregnancy accurately, the sonographer will measure your baby from the top of his head to the bottom of his spine. She will then measure the width of the NT. The skin will appear as a white line, and the fluid under the skin will look black.

You'll be able to see your baby's head, spine, limbs, hands and feet on the screen. Some major abnormalities may be ruled out at this scan, such as abdominal wall and skull defects. But it's recommended that you also have a detailed anomaly scan at about 20 weeks.

It may help if your partner or a friend accompanies you, to share the experience and be with you when you get the result.

What is a normal measurement?

An NT of less than 3.5mm is considered normal when your baby measures between 45mm and 84mm (FASP 2010). The NT normally grows in proportion with your baby (Nicolaides et al 1999).

The image on the right shows a baby with a normal NT of 1.3mm. This baby will be low risk. However, an increased NT does not mean there is definitely a problem. Some babies without Down's have increased fluid, too.

The image on the left shows a baby with an NT of 2.9mm, which is within the limit of normal range. Nine out of 10 babies with a measurement between 2.5mm and 3.5mm will be completely normal (Nicolaides et al 1999).

As the NT increases, so does the risk of Down's and other chromosomal abnormalities.
The baby in the image to the left has an NT of 6mm and has a high risk of Down's, as well as other chromosomal abnormalities (Witters and Frynns 2007) and heart problems (Wald et al 2008).

Fortunately, not many babies have as much fluid as this.

How is the risk of Down's calculated?

Every woman has a chance of giving birth to a baby with Down's syndrome. The chances increase with your age.

To calculate your risk, the sonographer will enter your age and the measurements from your NT scan into a database. It shows the risk that applies to all women of your age (the background risk).

Your scan measurements will be combined with your age to generate your own individual risk for this pregnancy. This may be higher or lower than your background risk. Many maternity units offer a combined test, which combines the blood test results with the NT measurement.

What should I do if I'm high risk?

Most women given a high risk (one in 150 or less) will go on to have a baby without Down's. Even with a risk as high as one in five, there's a four out of five chance that your baby does not have Down's. Nevertheless, once your pregnancy has been labelled high-risk, you will probably feel anxious and unsure of what to do.

The only way to know for certain if your baby has Down's or another chromosomal abnormality is to have a diagnostic test, such as CVS or amniocentesis. This decision can be very difficult, but you don't have to decide in a hurry.

One advantage of the NT scan is that it is done early in your pregnancy. It is possible to have a CVS and get the result while you are still in your first trimester. If you are unsure, you can wait until 15 weeks and have an amniocentesis if you wish. Your midwife or doctor will provide more information if you need it.

Will I be given a risk for any other abnormalities?

You will also be given a risk for Edwards' syndrome and Patau's syndrome, which are two other chromosomal abnormalities (Kagan et al 2008). These conditions are much rarer than Down's, and most affected pregnancies do miscarry. Babies with these conditions usually also have abnormalities that can be seen on the scan.

How accurate is the NT scan?

The NT scan picks up about 75 per cent of babies with Down's syndrome (Snijders et al 1998: 351).

Sometimes, a screening test can suggest that a baby has a high risk of having Down's syndrome, even though they don't actually have it. This is called a false positive. The false positive rate for an NT scan is five per cent. This means that one in 20 women is wrongly given a high risk.

Combining an NT scan with a blood test gives a more accurate result. The blood test measures the levels of the hormone free beta-hCG and the protein PAPP-A. Babies with Down's syndrome tend to have high levels of hCG and low levels of PAPP-A.

When the NT scan is combined with this blood test, the detection rate increases to 90 per cent (Nicolaides et al 2000, Kagan et al 2008). This is called the combined test.

Where can I have an NT scan?

NT scans are offered routinely at most NHS antenatal clinics, and the NT scan combined with the blood test is offered at 96 per cent of NHS hospitals in England. Find out which tests and scans are available on the NHS in your area.

The combined test is also available privately in some centres across the country, and is called the Oscar: One Stop Clinic for Assessment of Risk (Kagan et al 2008). Contact the Fetal Medicine Foundation for details of private screening in your area, or ask your midwife.


Kagan KO, Wright D, Valencia C, et al. 2008. Screening for trisomies 21, 18 and 13 by maternal age, fetal nuchal translucency, fetal heart rate, free {beta}-hCG and pregnancy-associated plasma protein-A. Hum Reprod. 23(9): 1968-75

NICE. 2008. Antenatal care: Routine care for the healthy pregnant woman. National Institute for Health and Clinical Excellence. [Accessed September 2012]

Nicolaides KH, Sebire NJ, Snijders JM. 1999. The 11-14 week scan; The diagnosis of fetal abnormalities. New York and London: The Parthenon Press Diploma in Fetal Medicine Series

Nicolaides KH, Cicero S, Liao AW. 2000. One-stop clinic for assessment of risk of chromosomal defects at 12 weeks of gestation Prenat Neonat Med. 5. pp.145-54

National Screening Committee, Fetal Anomaly Screening NHS. 2007. Standards for nuchal translucency measurement [Accessed September 2012]

Snijders RJM, Noble P, Sebire N, et al. 1998. UK multicentre project on assessment of risk of trisomy 21 by maternal age and fetal nuchal translucency thickness at 10-14 weeks of gestation. Lancet pp.351, 343-6

Wald NJ, Morris JK, Walker K, et al. 2008. Prenatal Screening for serious congenital heart defects using nuchal translucency: a meta-analysis. Prenat Diagn.28(12): 1094-104

Witters I, Fryns JR. 2007. Fetal nuchal translucency thickness. Genet Couns. 18(1):1-7

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Hello all the concerned mothers here.. I am 18 weeks pregnant.. I went for NT scan at 12 weeks n its 3.3 mm.n at that time my baby measured 68.4 has nasal bone.. My blood test was in normal range. V were assured by the genetic counselor that everything seems fine.. N v need not be worried.. Then I went for my anatomy scan yesterday n they saw one white spot in baby's heart.. I don't know what to do. M so scared. My husband doesn't want to for amnio.. Shall I go for NIPT test? Please post your valuable suggestions..
so, what did the harmony test say?
The Amnio/cvs is the only way to know for sure if your unborn baby has DS. My daughter has DS and the type that she has wouldn't be picked up on the harmony/nifty test as she still has 46 chromosomes. I would not waste my money on the harmony/nifty and I will be having a late amnio to find out if my second baby has any genetic conditions. X
POST FOUR: She then said when you go can we have a copy please. Cheeky! we have to pay 800 Quid plus train to get to London and they want a copy of the results yes for our benefit but they should pay something surely. Worrying went Doctor for his opinion said he never herd of it. WHY ARE NHS SO QUITE ABOUT PRVATE HOSPITAL AND TEST THE KNOW IS THRE BUT WONT GIVE INFORMATION OUT DISGUSTING! MY NT IS 1.8MM anything they say 1.3mm below is normal. I was told i am 1 in 75 chance of down syndrome. Well going for the test tomorrow and 2 weeks for results. We need to find out to get prepared for a child with downs if we have. NHS ARE AWFUL! dont have child at QMC was treated awfully and hospital is dirty.
POST THREE: We searched online at home if there is any other way and there is called a NIPT SCAN uk dont have the technology for this and it is new since 2013. You have to go private it is called a harmony scan. It is expensive can rang from 400-900 quid but worth every penny. Recommend to anyone if your worried. What happens is they just the blood from your arm and that's it. They send it to america results within 2 weeks. NO INJECTION INTO THE BABY SAK. NO WORRY OF MISCARRIAGE either please do this harmony test in case of miscarriage risk of healthy baby though the NHS amino injection xx. She told us that healthy babies have died with the injection it needs to go global. I understand some people cant afford it but please research it online! Then we rang her to tell her we are going for the test she doesnt know and was awful saying its not 100%. I said sorry we researched it going london private hospital its 99%. the injection is 98-99% accurate lower. She didnt like it.

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