Nuchal Translucency Scan

Author: Dr Monica Pahuja*

What is the nuchal translucency?

Nuchal translucency is the name for the normal fluid space behind the neck of a foetus (unborn baby) that can be seen on ultrasound scans.

What is a nuchal translucency scan?

Image of an ultrasound examination

A nuchal translucency scan (also called first trimester of pregnancy screening) is carried out during weeks 11–13 of a pregnancy. The scan uses ultrasound to screen for Down syndrome, or other chromosomal or inherited conditions in the foetus.

Other non-chromosomal conditions, such as neural tube defects, abdominal wall defects, limb abnormalities and some congenital heart disease, can also be detected at this stage of the pregnancy.

Screening can determine the likelihood of risk of an abnormality, but does not diagnose the condition. If screening does identify a possible risk, it does not necessarily mean there is an abnormality present, but does mean that further testing is necessary.

A nuchal translucency scan is combined with the mother’s age and results of a blood test showing the mother’s pregnancy hormone levels to provide a ‘combined risk’.

Without the blood test, screening is 75% accurate for predicting Down syndrome. With the blood test, the accuracy increases to 85%. Women who return a high-risk result from the screening will be offered formal genetic testing using other procedures, such as amniocentesis or chorion villus sampling (CVS).

All women are offered a nuchal translucency test regardless of their age, and 19 out of 20 women have a normal screening result.

Why would my doctor refer me to have this scan?

Any patient might be referred for a nuchal translucency test regardless of their age.  Your referring doctor (GP or obstetrician) will be able to tell you whether you are eligible for a Medicare rebate for the scan.

Your doctor would recommend a nuchal translucency scan:

• to confirm the exact date of the pregnancy and the due date;
• to confirm the number of foetuses (single or multiple);
• to confirm that the foetus is growing appropriately and appears to be developing normally;
• based on the age of the mother (the scan is strongly recommended for women who are over 35 years-of-age, as there is increased risk);
• if there is a prior history of pregnancy with a foetal abnormality;
• if there are genetic conditions in the family.

How do I prepare for a nuchal translucency scan?

There is very little preparation required. You should have some fluid in the bladder, but not be uncomfortably full. This is to ensure that the inside of the abdominal area is seen clearly on the ultrasound images. The radiology facility where you are having the ultrasound will provide you with information about this.

It is a good idea to wear comfortable clothing that gives easy access to your lower abdominal area.

To enable a ‘combined risk’ to be assessed (see ‘What is a Nuchal Translucency Scan’ above), a blood test should be ordered by your doctor between 10 and 12 weeks of pregnancy as part of the complete screening test.

What happens during a nuchal translucency scan?

The nuchal translucency is measured by carrying out an abdominal ultrasound scan from 11 weeks 4 days of foetal age to 13 weeks 6 days.

You will be asked to lie on an examination couch. Gel is applied to the lower abdomen area, and a transducer (a smooth handheld device) is moved gently across the abdomen with a sliding and rotation action. The transducer transmits ultrasound waves, which are relayed back to the ultrasound machine to produce images or pictures onto an ultrasound screen.

The ultrasound screening looks at many things, including the size of the foetus, the heart rate, the general anatomy or structure of the foetus and also how many foetuses are present (one or more).

At this stage, the foetus is too small to have a very detailed examination of its body structure: this is usually carried out at around 18 weeks, when the foetus is larger.

The nuchal translucency must be measured accurately, and can sometimes be difficult to obtain using an abdominal ultrasound scan because of the position of the foetus. Sometimes a transvaginal ultrasound might need to be carried out to allow this measurement to be taken. In a transvaginal ultrasound, a small specially shaped transducer is inserted into the vagina, and because the transducer is closer to the foetus, it can provide clearer images. If a transvaginal ultrasound is required, the procedure will be fully explained and your permission requested.

Are there any after effects of a nuchal translucency scan?

There are no after effects of an abdominal or transvaginal ultrasound. You will be able to resume normal activities immediately.

How long does a nuchal translucency scan take?

The scan takes about 30 minutes.

Sometimes the sonographer will ask you to wait in the ultrasound room after having the scan, so the images can be checked by the radiologist/sonologist (specialist doctor). Sometimes it will be necessary for the specialist to attend the examination to carry out more scans or to look at the images on the screen rather than just the still pictures taken during the scan.

What are the risks of a nuchal translucency scan?

There are no known risks of having an abdominal ultrasound to the foetus or mother. Ultrasound uses sound waves to obtain images and there is no radiation involved.

As many scans as required can be carried out without any increased risk.

There is no risk to the foetus or mother, or of miscarriage, if a transvaginal ultrasound is carried out.

What are the benefits of a nuchal translucency scan?

The main benefit of screening is to assess the possibility of Down syndrome or other foetal conditions as early as possible in the pregnancy. You will then have the opportunity to discuss the results with your doctor. If screening does identify a possible risk, you might require further definitive tests to confirm the screening results before deciding whether or not to continue with the pregnancy (see amniocentesis or chorion villus sampling).

Who does the nuchal translucency scan?

The examination is carried out by sonographers who are specially trained and accredited to carry out the scan. Sonographers may be male or female. If you are not comfortable with a male, you should let the reception staff know this before having the scan. In these cases where the patient is young or has religious or ethnic concerns, a female chaperone can be requested (usually a nurse at the radiology facility where you are having the scan, or a female parent or family member).

The sonographer might leave the room to show the images to the radiologist (specialist doctor) who provides a report to your GP or obstetrician. The radiologist might also carry out further scanning if something needs to be checked. A full report of the scan will be written and sent to your doctor.

In some radiology facilities, only the doctor or specialist will carry out the scan and will usually inform you of the findings.

Where is a nuchal translucency scan done?

The examination is carried out in a radiology department of a hospital, private radiology practice or at a specialist clinic for obstetric and gynaecological imaging. The ultrasound room is usually dimly lit to allow the images on the ultrasound screen to be clearly seen.

When can I expect the results of my nuchal translucency scan?

The time that it takes your doctor to receive a written report on the test or procedure you have had will vary, depending on:

• the urgency with which the result is needed;
• the complexity of the examination;
• whether more information is needed from your doctor before the examination can be interpreted by the radiologist;
• whether you have had previous X-rays or other medical imaging that need to be compared with this new test or procedure (this is commonly the case if you have a disease or condition that is being followed to assess your progress);
• how the report is conveyed from the practice or hospital to your doctor (in other words, phone, email, fax or mail).

Please feel free to ask the private practice, clinic or hospital where you are having your test or procedure when your doctor is likely to have the written report.

It is important that you discuss the results with the doctor who referred you, either in person or on the telephone, so that they can explain what the results mean for you.

Useful websites about nuchal translucency:

www.nhmrc.gov.au – See: nuchal translucency
www.sufw.com.au

*The author has no conflict of interest with this topic.

Page last modified on 23/10/2017.