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NT Scan (Nuchal Translucency) Explained

The nuchal translucency (NT) scan is part of your 12-week screening. It measures fluid at the back of your baby's neck to assess the risk of chromosomal conditions. Here's what you need to know.

Table of Contents

  1. What Is Nuchal Translucency?
  2. What's a Normal NT Measurement?
  3. What Happens If NT Is High?
  4. Combined Screening Test
  5. Frequently Asked Questions

What Is Nuchal Translucency?

Nuchal translucency is a fluid-filled space at the back of every baby's neck. All babies have this fluid, but babies with chromosomal conditions (like Down syndrome, Edwards syndrome, or Patau syndrome) tend to have more fluid, making the measurement larger.

The NT scan is performed as part of your routine NHS 12-week scan, usually offered between 11 weeks and 13 weeks plus 6 days. The sonographer takes a careful measurement of this fluid pocket in millimetres using a side-on image of your baby. This measurement is one piece of information — it is most meaningful when combined with your blood test results and your age-related risk.

It is important to understand that the NT scan is a screening test, not a diagnostic test. It estimates the likelihood of certain conditions but cannot confirm or rule them out. A straightforward result does not guarantee a baby is unaffected, and a higher measurement does not mean your baby definitely has a condition.

What's a Normal NT Measurement?

A normal NT measurement is typically less than 3.5mm at the 12-week stage. Most babies measure somewhere between 1mm and 3mm, with the expected range rising very slightly as gestational age increases within the scanning window.

A measurement over 3.5mm is described as increased or elevated. This doesn't mean your baby definitely has a condition — it simply means further investigation is recommended. Many babies with a measurement above this threshold are born completely healthy. The figure of 3.5mm is a screening cut-off, not a diagnosis.

Because the measurement is taken in millimetres, even small differences in technique or the baby's position can affect the reading. NHS sonographers are trained to take the measurement in a standardised way to reduce variation, but it is worth knowing that no measurement is absolutely precise to a decimal point.

What Happens If NT Is High?

If your NT is above 3.5mm, your midwife or screening team will explain your options. These typically include:
  • A consultation with a fetal medicine specialist — a doctor with specialist expertise in pregnancy and fetal wellbeing
  • NIPT (non-invasive prenatal testing) — a blood test that analyses fragments of your baby's DNA in your bloodstream; it carries no risk to the pregnancy
  • Diagnostic tests — CVS (chorionic villus sampling) or amniocentesis; these take a small sample of placental tissue or amniotic fluid for definitive chromosomal analysis, but carry a small risk of miscarriage

You are not obligated to pursue any of these options. Your screening team will give you time and space to ask questions and make the decision that is right for you and your family.

If the NT is significantly elevated (above 6mm in some guidelines), there is also a small chance of structural heart differences, so your team may recommend a specialist cardiac scan later in pregnancy.

Combined Screening Test

The NT scan alone gives only part of the picture. In the NHS, it is always combined with a blood test — typically taken on the same day or shortly before — which measures two proteins: PAPP-A (pregnancy-associated plasma protein A) and free beta-hCG. Together, this is called the **combined screening test**.

Your individual risk is then calculated using the NT measurement, the blood results, your age, your weight, and how many weeks pregnant you are. The result is expressed as a ratio, such as 1 in 800 or 1 in 50.

The NHS uses a threshold of 1 in 150 to define the results:

  • Lower chance: a result of 1 in 150 or lower (e.g. 1 in 5,000) — no further screening is routinely offered
  • Higher chance: a result of 1 in 150 or higher (e.g. 1 in 80) — further testing is offered

Results are usually available within a few days and are shared by your midwife or maternity team, often by letter or through your NHS app or handheld notes.

Frequently Asked Questions

### What NT measurement is concerning?

A measurement above 3.5mm is considered increased and triggers further discussion with your screening team. However, "concerning" is relative — many babies with elevated NT are perfectly healthy. Your overall combined screening result, which factors in blood tests and your age, gives a more complete picture than the NT measurement alone.

Can I refuse the NT scan?

Yes. All screening tests in pregnancy are optional. You can decline the NT scan and/or the combined screening test. Your midwife will explain the options clearly and respect your decision without judgement. Some parents choose not to screen because they would not act on a higher chance result; others want information regardless. There is no right or wrong choice.

How long does it take to get NT scan results?

The NT measurement itself is available immediately — the sonographer will usually tell you the number during your scan appointment. The combined screening result, which incorporates your blood test, typically takes a few working days. Your maternity team will contact you, so you do not need to chase results unless you have not heard within two weeks.

Further reading:

Always speak to your midwife or GP if you have questions about your NT scan or screening results — they can explain what the figures mean for your specific situation.

Last reviewed: June 2026

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