Ultrasound - Nuchal Translucency


Nuchal Translucency is a small layer of fluid at the back of your baby's neck and is situated between the skin and the surrounding soft tissue. All babies have this layer of fluid but in the case of a chromosomal abnormality, the thickness of the layer tends to be increased.

A Nuchal Translucency Scan (NTS) measures this thickness and is used to screen for chromosomal abnormalities, the most common of which is Down Syndrome. The procedure may also detect a major heart abnormality and/or certain structural defects.

Should I have the NTS performed?

The vast majority of babies are normal. However all women, whatever their age, have a small risk of developing a baby with impaired physical and/or mental function. In some cases, this is caused by a chromosomal abnormality such as Down Syndrome. While the decision to have an NTS should be made in consultation with your doctor, the procedure itself is safe and noninvasive, and remains one of the most sensitive screening tests on offer today. In determining whether you need the scan, your doctor will consider factors such as your age, and any previous or family history of abnormal pregnancies.

When is the scan performed?

The nuchal translucency is only present in the early stages of your baby's development. The scan should therefore be performed while your pregnancy is between 12 and 13 weeks.

How is the scan performed?

An NTS is like any other ultrasound procedure. However, the sonographer performing your examination must be accredited by the Fetal Medicine Foundation whose work established the test and maintains the strict standard by which the scan should be carried out.

During the scan, images are acquired using sound waves that carry no risk to yourself or your unborn child. In the majority of cases NTS images are obtained externally. A layer of gel is spread over your belly before a probe is massaged over the area to obtain the required images. In very rare cases, we may also require an internal scan to obtain the best possible images. This involves placing a small probe into your vagina and is not harmful to the pregnancy.

To increase the accuracy of the NTS, it is usually performed in conjunction with a blood test known as 'first trimester serum biochemistry'. This blood test is used to measure the levels of two hormones: (1) free ß-hCG and (2) PAPP-A. In pregnancies affected by Down Syndrome there is a tendency for the levels of free ß-hCG to be increased and PAPP-A to be decreased.

If available, the results from your blood test will be combined with the results of your NTS, together with other factors such as your age, to generate a risk factor for your pregnancy. This risk factor is expressed in the "1 in x" format, for example 1 in 1,000 or 1 in 300. The combination of an NTS and a blood test in determining risk provides a 90% detection rate of chromosomal abnormalities.

How do I make an appointment?

Once your doctor has written a referral you will need to contact us to make an appointment. Appointments can generally be made for the following day but it is important that if you also require a blood test, this should be performed prior to your NTS appointment. Blood tests can take up to 5 days to be reported. To ensure your results are available for your NTS, it is advisable to request that they be sent to Territory X-ray Services.

For further information

While this information is designed to be as informative as possible, it is very brief in nature and should not replace the advice or guidance of your doctor or preferred healthcare professional.