Discussions on "NT Screening" in "I am pregnant" forum.
24th Nov 2011, 09:32 PM #1
Nuchal Transluency Screening(NT Screening)
What is the nuchal translucency screening test?
- This prenatal test (also called the NT or nuchal fold scan) can help your healthcare practitioner assess your baby's risk of having Down syndrome (DS) and some other chromosomal abnormalities as well as major congenital heart problems.
- The NT test uses ultrasound to measure the clear (translucent) space in the tissue at the back of your developing baby's neck.
- Babies with abnormalities tend to accumulate more fluid at the back of their neck during the first trimester, causing this clear space to be larger than average.
- The NT scan must be done when you're between 11 and 14 weeks pregnant. (The last day you can have it done is the day you turn 13 weeks and 6 days pregnant.) It's usually offered along with a blood test in what's known as first-trimester combined screening.
- Like other screening tests, an NT scan won't give you a diagnosis. But it can assess your baby's risk for certain problems and help you decide whether you want to have chorionic villus sampling (CVS) or amniocentesis to find out whether your baby is actually affected.
- Because the NT scan requires special training and equipment, it's not yet available everywhere. But the test is being done more widely as more medical personnel get trained and certified. If you're interested, ask your healthcare practitioner or genetic counselor whether it's offered in your area.
24th Nov 2011, 09:38 PM #2
Re: NT Screening
How is a NT scan done?
- The nuchal translucency scan is usually an abdominal scan. Depending on the position of your baby and your womb however, a vaginal scan might be necessary to get an accurate image.
- Like other abdominal scans of your first trimester, you will need to have a full bladder.
- The doctor will start by measuring your baby from the top of its head to the bottom of the spine. She will then measure the width of the NT.
- The baby's skin will appear as a white line, and the fluid under the skin will look black.
- Your baby fits nicely on the screen at this stage, and you will be able to see the head and spine, limbs, hands and feet.
An NT measurement of up to 2.0mm is normal at about 11 weeks, and up to about 2.8mm by 13 weeks and 6 days. This is because the NT normally grows in proportion to the growth of the baby.
Image 1 shows a baby with a normal NT of 1.3mm; this baby will be low risk.
1. Normal nuchal translucency
If the NT is increased, it does not mean there is definitely a problem. Some normal babies have increased fluid, too. Image 2 shows a baby with an NT of 2.9mm, which is at the upper limit of the normal range. Though the risk will be higher than the baby's in the first image, nine out of 10 babies with a measurement between 2.5mm and 3.5mm will be completely normal.
2. Borderline nuchal translucency
As the NT increases, so does the risk. The baby in image 3 has an NT of 6mm and will be at a very high risk for Down's, as well as other chromosomal and genetic syndromes and heart problems. Fortunately, not many babies have as much fluid as this.
3. Increased nuchal translucency
24th Nov 2011, 09:41 PM #3
Re: NT Screening
Where can I have a nuchal translucency scan?
Most private diagnostic centres that offer other antenatal scans do nuchal translucency scans as well. Some hospitals offer the scan as part of their antenatal package. Just make sure that the clinic or laboratory you go to is well-equipped and the sonographer is trained and experienced.
When will I get the results?
It usually takes a day for the ultrasound report to be ready. If you are getting your scan done at the same hospital in which your doctor practices, the report will be sent directly to your doctor. Your doctor will then discuss the results with you at your next appointment. If you get your scan done at a diagnostic centre, your results will be on the internet by the evening but you will have to go back the next day to collect the report. Sometimes, diagnostic centres deliver reports within a few hours but you will have to ask specifically for this.
What do the results mean?
- The results will express the probability of your baby having Down's syndrome. They will be given in the form of a ratio. For example, 1:800 means that out of 800 women who have this risk level, one will have a baby with Down's syndrome.
- Low risk is a result where the risk is less than one in 300 such as 1:500.
- High risk is a result where the risk is greater than one in 300, for example, 1:150. This means that out of every 150 women who have this risk, one will have a baby with Down's syndrome.
24th Nov 2011, 09:44 PM #4
Re: NT Screening
What should I do if my baby is at high-risk of having Down's?
- About one in 20 women have a high risk, and the vast majority of them will go on to have a normal baby.
- Even with a risk as high as 1:5, there is only one chance out of 5 that the baby will have Down's.
- Nevertheless, once your pregnancy has been labelled high-risk, you will probably feel anxious and perhaps unsure of what to do.
- The only way to confirm Down's is to have a diagnostic test such as CVS or amniocentesis. This decision can be very difficult, but you do not have to decide in a hurry.
- One advantage of the NT scan is that it is done early in your pregnancy, so it is possible to have a CVS while you are still in the first trimester.
- A large research study involving over 100,000 pregnancies found that about 75 per cent of babies with Down's syndrome were correctly identified using this method.
- When combined with a blood test, the detection rate improves to about 90 per cent.
- However, to achieve these detection rates, it is important that the NT is measured accurately. This is why the scan should only be done by a trained professional.