What is the nuchal translucency scan?
The nuchal translucency ultrasound is performed in the first trimester of pregnancy between 11 weeks and 3 days of pregnancy and 13 weeks 6 days.
The scan is offered to pregnant women to determine which pregnancies are at higher risk of chromosomal anomalies, particularly Down Syndrome (Trisomy 21), but also Trisomy 13 and 18.
This is done by measuring the thickness of a fluid layer deep to the skin at the back of the baby’s neck, the nuchal translucency. The fluid is present in all babies during early pregnancy and appears on ultrasound as a black space (translucent).
During the nuchal translucency scan we are also able to:
- Confirm your due date
- Diagnose multiple pregnancies
- Diagnose early pregnancy failure
- Check the normality of fetal anatomy that is visible at this stage
Before 11 weeks 3 days the baby is too small to properly visualise the anatomy and after 14 weeks the nuchal fluid is reabsorbed and the test cannot be performed. Therefore, it is important to be sure of your dates when booking your scan.
Why have a scan at 11-14 weeks and what does it involve?
Currently the most accurate non invasive test for detecting Down syndrome during pregnancy is the measurement of the nuchal translucency with ultrasound between 11weeks 2 days – 13 weeks 6 days of pregnancy. Research has shown that increased thickness of the nuchal translucency is associated with an increased risk of Down Syndrome and other chromosomal abnormalities1.
In the majority of patients the ultrasound scan is performed with the probe on the abdomen however occasionally, a vaginal scan may be required to obtain satisfactory images.
Please advise our reception staff if it is a multiple pregnancy (twins or triplets) as we will need to allocate more time for your examination.
How do I prepare for a Nuchal Translucency scan?
You will be required to drink water (up to 500ml) a full hour before your appointment time. This gives the water time to enter your bladder. These scans initially require a semi-full bladder (but not uncomfortably full) in order to visualize the baby. In the majority of patients the baby can be seen well enough with the ultrasound transducer placed on the lower abdomen however occasionally, a vaginal scan may be required to obtain satisfactory images. This internal examination is neither harmful to your pregnancy nor painful.
How is the risk calculated?
The accredited sonographer combines the following first trimester information:
- The background risk due to the mothers age
Every woman has a risk of having a Down Syndrome pregnancy, and this risk increases with age. At 20 years of age the risk at 12 weeks of pregnancy is 1:1070 and by the age of 40 it has increased to 1:70.
- Measurement of the nuchal translucency
The measurement of fluid obtained at the back of the babies neck (during the ultrasound performed ideally around 12 weeks)
- A blood test called a 'First Trimester Blood Test' (Beta HCG, PAPP-A)
Performed after 10 weeks (optimally 2 weeks before your ultrasound) or at the latest 2 working days before the scan.
This information is entered into a specially designed computer program to calculate the risk, which is expressed as a ratio.
- A low risk is a result where the risk is less than 1 in 300 ( for example 1:1000)
- A high risk is a result where the risk is greater than 1 in 300 (for example 1:50).
How accurate is the nuchal translucency scan?
The nuchal translucency scan combined with a first trimester blood test can place approximately 90% of babies with Down syndrome into a high risk category. No screening test is 100% sensitive for detecting all cases of Down syndrome. About one in 20 women will be placed in the high risk category, however the majority will go on to have a healthy baby.
A definitive way to determine if your baby has a chromosomal abnormality would be with prenatal tests such as Chorionic Villus Sampling (CVS) or Amniocentesis. These are invasive tests that require introducing a needle into the mother’s womb to test the fetal cells. Your doctor will be able to provide information about these tests and the associated risks. These tests are available with specialist women’s clinics.
2nd and 3rd Trimester Scans
Structural problems are best detected at the 20 week Morphology scan. Between 19-22 weeks a detailed scan of the baby’s heart, brain, and major organs can be performed to detect problems (eg. spina bifida). These ‘morphology’ scans may take up to an hour to complete as we aim to provide you with the highest quality scan. We also may be able to assess the gender of your baby and perform 4D ultrasounds (the quality of the 4D ultrasound is dependent on the position of the fetus and fetal age. A CD of the images can be supplied for you to take home.
It is not necessary to scan your baby in the third trimester unless your doctor thinks it is clinically warranted.
What are the costs of a Nuchal Translucency Scan?
The cost to you of a Nuchal Translucency scan depends on a number of factors and whether the scan qualifies for a Medicare rebate. There is a long list of clinical conditions which allow the scan to qualify for a medicare rebate. The sonographer will discuss whether you qualify for a rebate on the day of your scan.
When booking an appointment at Qscan you should ask about any costs to you.
Where is a Nuchal Translucency Scan done?
Nuchal Translucency scans are done at Qscan’s Windsor and Annerley clinics and limited bookings at the Mater Private Qscan Radiology Clinic.
You will need to contact Qscan Radiology Clinics and make an appointment for your ultrasound.
Remember to bring any previous films from your current pregnancy to the scan.
Where to find further information?
If you would like to know more about Nuchal Translucency scans, ask the staff at Qscan Radiology Clinics to which you have been referred. More information can be found at http://www.fetalmedicine.com/fmf/
Feel free to discuss any questions or concerns about having an Ultrasound scan with the Qscan staff or your referring doctor.
Who is involved in my scan?
World-class radiologists and outstanding Sonographers, all of whom are accredited and have undergone extensive training, staff Qscan Radiology Clinics.
One of the Qscan radiologists will view the images produced from the test and provide a report for your referring doctor.
A radiologist completes a medical degree followed by at least two years in general clinical training and then a five year specialist training program.
The Royal Australian and New Zealand College of Radiologists (RANZCR) conducts the specialist training program and sets professional standards for radiologists.