Nuchal Translucency Scan

The nuchal translucency (NT) scan is a pioneering test that screens babies for Down’s syndrome during pregnancy. It is currently the most accurate method for estimating the threat of Down’s without diagnostic testing. The scan applies ultrasound technology so the procedure is also non-invasive and painless. It also checks for the much rarer conditions of Patau’s syndrome and Edwards’ syndrome.

What is nuchal translucency?

Nuchal translucency is the fluid collected between two layers of the baby’s skin on the rear of the baby’s neck. This fluid is found in all babies, but studies have found that a majority of babies with Down’s syndrome possess an increased quantity of fluid.

What does the nuchal translucency scan involve?

You will be scheduled for an ultrasound between 11 and 14 weeks into pregnancy. This timing ensures that the baby is not too small for the test to be effective, and not too developed that any surplus fluid is naturally absorbed. A scan of the vagina may afford a more precise view of the baby, especially if the test is taken early, but most NT scans are taken through the abdomen. Like with a dating scan, the sonographer measures the baby’s crown to rump length in order to calculate the baby’s age. They then calculate the size of nuchal translucency, which appears on the scan as black between white lines of skin.

Estimating risk

As the threat of delivering a baby with Down’s syndrome amplifies with age, the sonographer uses the mother’s age in addition to the NT measurements, the baby’s heart rate and results from relevant blood tests. They enter these figures into a record containing the general risk for mothers of this age, and both the age and measurements are then mixed to calculate an individual risk factor. Depending on the NT measurement, your risk can be greater or less than the general risk for women your age. The results are available immediately and are in the form of a probability, such as ‘the chance of 1 in 200.’

Can I bring people along?

Yes. There is usually no reason why you cannot bring your partner, a friend or family member with you for support and to share the moment of seeing your baby. Anxiety is natural when getting the result, so extra support is always welcome.

Is the scan accurate?

The NT scan is a screening test, meaning it is limited to estimating risk, but it does identify about 75% of babies with Down’s. A diagnostic test like amniocentesis or CVS is able to provide a solid diagnosis, but these carry their own pros and cons, including a minor risk of miscarriage, and an NT scan is a safe way to help decide if you require a diagnostic test or not. False positives occur in 5% of cases, meaning that the baby is incorrectly found to be high risk. This is far less likely when the scan is accompanied by a blood test.

What does high risk mean?

If the risk is estimated as one in one hundred and fifty or fewer, this is counted as high risk. However, you must remember that these are still good chances, and even a baby with a threat of one in ten would still be free of the condition nine times out of ten. Anxiety and upset are nevertheless natural for parents with a high risk baby, and diagnostic tests can tell you for certain either way. Amniocentesis can be performed in the 16th week, giving you time to reflect and decide whether to have the test.

Is the scan readily available?

Approximately 7% of women receive an NT scan on the NHS; others may need to go private. Privately the scan can cost between £90 and £150, and you should check any private practice’s accreditation with the Fetal Medicine Foundation. The NHS rarely offers the more accurate scan using a blood test. Ask your doctor or midwife for recommendations.