What is a Nuchal Translucency scan?
A screening teat for Down Syndrome. An ultrasound scan done between 11.5 and 14 weeks of pregnancy to where there is measurement of the amount of fluid in the skin at the back of the baby's neck. It is usually performed through the abdominal wall but sometimes it is necessary to do an internal (vaginal) scan. The ultrasound has no known harmful effects on the mother or the baby.
All babies at this stage in pregnancy have some fluid in this area, but a baby with Down syndrome or another chromosome abnormality tends to have more fluid.
This ultrasound also checks for the presence of your baby’s heart beat, single or twin pregnancy, dates, exclusion of some other abnormalities.
Is a Nuchal Translucency scan accurate?
Yes about 70%.
The accuracy is increased to 90% if combined with a blood test called the maternal serum screening test.
The maternal serum screening test measures the amount of two different proteins called PAPP-A and beta HCG which occur naturally in the mother's blood during pregnancy. A change in the level of these proteins may indicate that there is an increased risk that the baby has Down syndrome.
What does an 'increased risk' of Down syndrome result mean?
1 in 20 women will have an 'increased risk' result. This does not necessarily mean that there is a problem in your unborn baby. It means that further tests should be considered to see if there is a problem with your baby. In most cases this will mean a Chorionic Villus sampling or amniocentesis and an 18 week scan.
What does a 'low risk' of Down syndrome result mean?
19 out of 20 women tested will have a 'low risk' result. This means that the risk of having a baby with Down syndrome is very low but does not mean that there is no risk.
It is very important to realise that this test is only for Down syndrome and that a 'low risk' result does not ensure that the baby is free of other possible birth defects
Does the test pick up any other birth defects?
Yes. Cardiac defects, skeletal defects and other chromosomal abnormalities can also be suspected.
Do I have to have both types of the test?
No, the decision is your choice entirely, but the combination of the two tests allows a more accurate result.
Do all pregnant women have the screening test for Down syndrome?
No. The decision whether or not to be tested is entirely up to you. You need to ask yourself whether you would do anything with result. If no then you need to carefully consider why you would have the testing done. While the Nuchal Translucency scan and the maternal serum screening test are noninvasive, an amniocentesis or CVS are invasive and carry a small risk of miscarriage (1 in 100). You would be tempted to get this done if your screening result indicated a high risk.