What is Nuchal Translucency?
All developing babies have a layer of fluid on the back of their bodies between the skin and the underlying soft tissue. This layer is translucent on ultrasound and its thickness is measured at the level of the neck. This is called the Nuchal Translucency measurement.
Research of greater than 100,000 instances of 11 week 3 day pregnancies to 13 week 6 day pregnancies has shown that there is an association of increased risk of chromosomal abnormalities or heart defects with increased thickness of the nuchal translucency.
All women have a risk of delivering a baby with a chromosomal abnormality and this risk is increased with maternal age. Down Syndrome (Trisomy 21) is the most common of the chromosomal defects and has always been difficult to detect before birth.
What is the Nuchal Translucency Assessment?
The Nuchal Translucency examination is offered to pregnant women to assess major chromosomal congenital anomalies. The test suggests which pregnancies are at a higher risk of abnormality and may need further investigation. A normal result does not guarantee a normal baby but does imply that an abnormality is unlikely. An abnormal result does not mean the baby is abnormal but suggests the baby should be further investigated.
This test is a measurement performed during an ultrasound examination between 11 weeks and 3 days of pregnancy and 13 weeks and 6 days of pregnancy. It is painless and carries no risk to the pregnancy. In a large majority of patients the ultrasound is performed with the probe on the abdomen but in a small percentage a scan performed through the vagina may be required.
What else can the 11-14 week scan assess?
At this early ultrasound we can:
- confirm that you are pregnant and determine the age of the fetus,
- diagnose multiple pregnancies, and
- examine the baby for some major defects.
A further ultrasound at 18 to 20 weeks is recommended as this is the best time to detect the majority of structural defects.
Additional Risk Assessment Available
The ultrasound examination can now be performed in combination with a blood test. This blood test is called Free Beta HCG and PAPP-A quantification. The ultrasound alone detects approximately 80% of abnormalities. With the addition of the blood test this can be increased to 85%. The blood test is best performed at approximately 10 weeks with the ultrasound at 12 weeks gestation. This blood test cannot be performed until 10 weeks and should be done at least 3 working days prior to the ultrasound scan.
The blood test is available from Sullivan Nicolaides Pathology throughout Queensland.
Should I have this test performed?
This is a question each parent must answer for themselves.
The main reason for performing screening tests such as this is to detect abnormalities. This allows consideration of further invasive testing or possible termination of pregnancy if an abnormality is found.
Patients most likely to benefit from this test are older women who are pregnant (as older women have a higher risk of chromosomal abnormalities), women who have had an abnormal pregnancy previously and women with a family history of abnormal pregnancies.
Who will perform the scan?
An accredited sonographer or radiologist will perform the scan. They will have passed exams specifically for Nuchal Translucency assessment.
After combining Nuchal Translucency (NT) measurement with your age (and blood tests if available) and utilising a specially designed computer program, we can calculate your risk of having a baby with a chromosomal abnormality for this pregnancy.
This risk will be expressed as "1 in…". A low risk is expressed as 1 in more than 300. A high risk is expressed as 1 in less than 300.
When will I get the results?
The results will be available shortly after the examination is complete. You can either wait for your results or alternative arrangements can be made to collect them at a later stage.
What if I’m shown to be high at risk?
If the NT examination determines your baby is at an increased risk of a chromosomal abnormality you should discuss this result with your referring doctor. This does not mean the baby is abnormal but indicates further tests may be needed. Most high risk pregnancies will be normal. Your doctor will be able to provide advice about further testing, such as chorionic villus sampling (CVS) or amniocentesis, to assess chromosomal abnormalities.