This test is done between 12 and 13.5 weeks by a Transabdominal scan.
The first trimeser nuchal translucency is a screening programme to find out your chance of having a baby with a major chromosomal abnormalities such as Down's Syndrome . The test has 2 parts;
1. An ultrasound measures the depth of fluid at the baby's neck called the nuchal translucency. (pronounced as 'new-cal').
2. A special blood test that measures the levels of two hormones- free beta HCG and PAAP-A. The blood test can be done between 10 - 14 weeks. The blood test poses no risk to the baby but you do have to have a needle. We will send you a blood form if you do not have one already.
At Tara we request that you have the blood test done at least 3 to 4 days before the scan.
If you have the blood test done a few days before your scan we should be able to give you your final risk figure after the scan. The doctor will speak to you personally about your risk and what the numbers mean. If the test places the pregnancy at a high risk of Down's Syndrome you may choose to do more invasive tests to determine if the baby has the condition.
What information will this test provide for me?
If you have the blood test done a few days before your scan we should be able to give you your final risk figure on the day. The doctor will speak to you personally about your risk and what the numbers mean.
If the test returns a high risk you may choose to do more invasive tests such as Amniocentesis to determine if the baby has a chromosomal condition.
The number that this test provides is a risk.
A 1 in 2 risk means that if you had 2 babies 1 would have a problem and one would not, that is a 50% chance. A 1 in 2000 risk means you would have to have 2000 babies (all at the same time) and 1999 of them would be normal but one would have a problem.
It is not impossible that you could have a baby with Down's syndrome with a 1 in 2000 risk but it is highly unlikely.
If the test does not rule out anything why have it done at all?
The main reason is it is a very early, accurate test. It allows you to make early decisions about what followup tests you may have if the risk is increased. Some of these tests cannot be done later in the pregnancy. If you decide not to continue the pregnancy then the earlier this is done the better it will be for you.
The doctor will discuss your options with you if the risk is increased. For most people this is an incredibly difficult and traumatic decision, there is no right answer. At Tara we will counsel and support you through this process.
Procedures that do give definite answers such as Amniocentesis and CVS carry a risk of miscarriage. The quoted risk is 1 in 100 for these procedures. Most Nuchal tests give a result that is much better than this. The 1 in 100 risk of losing the baby has to be weighed against the risk number that the Nuchal Test gives.
If you decide not to have the Nuchal Translucency test done we do recommend that you make sure you have the 18 week morphology scan. This is a more thorough test and will provide much more information as to the health of your baby. If there is a problem however there will be less options available to you because the test is 6 weeks later in the pregnancy.
What is Down's Syndrome?
Down syndrome is also known as trisomy 21. It occurrs when there is an extra or third copy of chromosome number 21 in body's cells.
This changes the normal genetic make up of 46xx or 46xy to 47xx, +21 or 47xy, +21.
The characteristics may include intellectual delay, distinct facial features and problems with the heart and digestive system.
Who can do this test?
The ultrasound specialists and sonographers who are accredited to use the Fetal Medicine Foundation database (LONDON) are allowed to perform the test.
At TARA, both the the specialists and the sonographers are accredited to perform the test.
How accurate are the results?
If you have both the ultrasound and the blood test about 90% of the babies with Down's syndrome will have an increased risk result. Around 10% of the babies with Down's can be missed.
About 5% of women scanned will have an increased risk. Most of these babies will be normal. There are further tests required to be sure the baby does in fact have down's syndrome.
This test does not find all abnormalities. A morphology scan at 18 weeks will look for other problems once the baby is bigger.
Can I just have the ultrasound?
YES. We would recommend you have the harmony test done as well because the results of the ultrasound alone are 75% accurate which means that 75% of babies with Down syndrome will receive an increased risk result. About 25% of the babies will be missed. Without the blood test the scan becomes a First trimester morphology scan. The cost of this ultrasound is the same whether you have the blood test done or not.
Everyone has a choice to have the test. Some women will chose not to have the test.
However, at TARA we combine the nuchal translucency test with an early anatomy scan.
This gives accurate dates and it is reassuring to see normal anatomy this early. It offers you more options and informs you of available therapies if a problem is identified.
It is also an opportunity to see your baby when it is 4.5 cm to about 8 cm long.
Other conditions that can be identified include twins and chromosomal problems Trisomy 13 and 18.
Nuchal measurement on ultrasound