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How Accurate is the Nuchal Scan?

One of the main purposes of the nuchal scan is to assess the risk of chromosomal abnormalities such as Down’s syndrome. The size of the nuchal fold at the back of the neck can be a good indication of this risk when it is measured during ultrasounds taken between 11 and 14 weeks. However, the scan cannot diagnose a chromosomal abnormality. It can only tell us if there is a higher than normal chance of one.

nuchal scan

Understanding Your Nuchal Scan Results

When you have a nuchal scan, the doctor or sonographer will measure the width of the nuchal fold, a fluid-filled area at the back of the baby’s neck. The size of the nuchal fold usually falls within a certain range that depends on the size and age of the baby. If the measurement is outside this range then it indicates a higher than usual chance of certain chromosomal abnormalities. However, the test isn’t perfect:

  • The nuchal scan can’t identify every baby with a chromosomal abnormality. For example, if 100 babies with Down’s syndrome are scanned, only 85 of them would show up as having an unusual nuchal fold. The rest would be missed.
  • Some babies may be classed as high risk even though they don’t have any abnormalities. If 100 babies without any chromosomal abnormalities are scanned, 5 of them would produce a high risk result.

It is therefore important to understand that the nuchal scan results can only tell you if your baby has a high or normal risk of chromosomal abnormalities.

What Next?

Although the nuchal scan can’t be used to diagnose a chromosomal abnormality, it is a very useful screening test during pregnancy. The results can help to guide your decisions about further tests. For example, if the scan suggests that there is a higher risk of an abnormality, you may want to have non-invasive prenatal testing (NIPT) to learn more. You will be able to discuss the results of the nuchal scan and other screening tests with your doctor to ensure that you understand what they mean for you and your baby.

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Clinic Locations

Visit our clinic in Central London and Cheshire


137 Harley Street, London W1G 6BF
Nearest Underground Tube Stations

Baker Street
Regent’s Park
Great Portland Street


Alderley Edge Medical Centre, Talbot Road, Alderley Edge, Cheshire, SK9 7HR
Nearest Overground Train Station

Alderley Edge