Nuchal translucency scan

A nuchal translucency scan is an ultrasound scan that measures the thickness of the space behind your baby's neck.

This measurement can help your doctor estimate the chance your baby has certain conditions such as Down syndrome. It is part of the combined first trimester screening test.

At the same time the sonographer can also:

• perform a dating scan
• find out if you are pregnant with twins
• measure other physical structures of your unborn baby

There is a small chance that your baby can be born with a congenital anomaly (birth difference). Screening is offered to everyone during pregnancy.

The chances of conceiving a baby with a genetic disorder are greater the older you are . If you are aged over 35 years, or there are genetic conditions in your family, your doctor may recommend this scan.

Most nuchal translucency scans do not find any problems. But about 5 in every 100 women get a 'high risk' result from combined first trimester screening.

Do I have to have a nuchal translucency scan?

Pregnancy ultrasound scans are optional. During pregnancy, you, your doctor and midwife can decide together which antenatal tests you should have. You may decide not to have any screening tests.

You will be given information about each test so that you can make an informed decision.

A nuchal translucency scan can be done after 11 weeks and before 14 weeks of pregnancy.

A nuchal translucency scan is usually performed by a specially trained technician called a sonographer. The scan is performed in a radiology clinic, a specialist clinic or a hospital.

A nuchal translucency scan is done using a handheld ultrasound wand. The wand may be placed on your abdomen (tummy) or in your vagina. Your sonographer will decide based on things like:

• how far along your pregnancy is
• the position of your baby
• your body shape

The ultrasound wand or probe transmits ultrasound waves. The soundwaves are sent to your baby and back to the ultrasound machine to produce images or pictures on the screen.

Tummy ultrasound

If your scan is done through your abdomen you should not urinate (wee) before the scan. This makes it easier to see inside your uterus (womb).

The sonographer will apply some gel and gently move the handheld ultrasound wand across your abdomen. It doesn't usually hurt.

Vaginal ultrasound

If your scan is done through your vagina, the sonographer will gently insert a small, lubricated ultrasound probe. The probe may be a little uncomfortable but isn't usually painful.

Scans done this way can give clearer pictures because the probe is closer to your uterus. If a vaginal probe is needed, the sonographer will explain what is happening first.

How should I prepare for a nuchal translucency scan?

It's a good idea to think carefully about why you are having a nuchal translucency scan. Consider what you would do next if your screening tests show that there is a high chance of your baby having a problem. Talk this over with your partner, a friend or family member.

On the day, drink a few glasses of water so that there is fluid in your bladder when you arrive. Wear loose clothes so that the sonographer can easily reach your abdomen.

If you are having the combined first trimester screening, you will also need a blood test.

Can a nuchal translucency scan harm my baby?

Ultrasounds do not harm you or your baby or increase your risk of miscarriage. No needles or radiation are used.

This scan usually takes about 30 minutes. Ask your doctor or sonographer when your results will be available.

The ultrasound clinic will send a full report to your doctor. The full results may take 7 to 10 days.

Your nuchal translucency scan measurement is combined with a blood test to work out the 'combined first-trimester screen' result. The calculation also includes your age.

This is a screening test, so the results can't tell you for sure whether your baby has a genetic condition. Results are usually reported as 'low risk' or 'high risk'.

If you have a 'low risk' result, it means it is less likely that there is an abnormality present. If you have a 'high risk result' it means it is more likely that there is an abnormality present.

If your test returns a 'high-risk' result, your doctor can refer you for further testing. You may decide to have a diagnostic test, which can give you a definite result. You can also go for genetic counselling to help you understand the result.

Diagnostic tests for your baby include:

• chorionic villus sampling (tests the placental tissue)
• amniocentesis (tests the amniotic fluid — the fluid around your baby)

In some cases, Medicare will cover the cost of your nuchal translucency scan. You may have to pay out-of-pocket costs, depending on where you go for the test.

Ask about the cost when you book your appointment.

Yes. You can bring your partner, family member or friend to your ultrasound appointments.

It can be good for someone else to listen to the information provided so that you can chat about it afterwards.

Non-invasive prenatal testing (NIPT), also known as cell-free DNA testing (cfDNA), is another antenatal screening test for chromosomal abnormalities.

It is more accurate than a nuchal translucency scan or combined first trimester screening. NIPT is not currently funded by Medicare and can be expensive.

Talk with your doctor or midwife for advice about which antenatal screening method is right for you.

Questions for your doctor

Here are some questions you might want to ask your midwife or doctor:

• Why are you offering me this test?
• What does the procedure involve, do I need to do anything on the day?
• When will I get the results?
• Who will give me my results?
• Do I need to do anything to care for myself after the procedure?

See some more questions to ask your doctor about tests and scans.

Your doctor, obstetrician or midwife can answer your questions and give you more information on antenatal screening tests.

A genetic counsellor can help guide you through the meaning of your results and any decisions you may need to make. The best way to find a genetic counsellor is to ask your doctor to refer you to one.

The Human Genetics Society of Australasia also has a Find a Genetic Counsellor service. It can help you find a registered counsellor nearby.