A new blood test for Down syndrome, Edwards Syndrome and Patau Syndrome.
Non-invasive prenatal testing (NIPT) is a new approach to testing whether a baby may be affected by a chromosome disorder. From a small sample of the mother’s blood, we are able to identify certain chromosomal conditions, such as Down syndrome.
During pregnancy, some of the baby’s DNA circulates in the mother’s blood stream. DNA is the substance that our chromosomes are made of and contains all our genetic information.
Usually, each human being has 46 chromosomes, arranged in 23 pairs. Occasionally, a baby is born with three copies of a particular chromosome, rather than two. This is known as a trisomy. The most common trisomies are Down syndrome, Edwards syndrome and Patau syndrome.
By analyzing the baby’s DNA found in the mother’s blood, we can detect whether or not there are abnormalities in the baby’s chromosomes.
What is Non-Invasive Prenatal Test (NIPT)?
Non-invasive prenatal testing (NIPT) analyses foetal ‘cell-free’ DNA circulating in the pregnant mother’s blood. Foetal cell-free DNA (cfDNA) results from the natural breakdown of foetal cells (presumed to be mostly placental) in the mother’s circulatory system. It clears from her system within hours of giving birth.
People usually have 46 chromosomes in each cell, but occasionally, extra copies of chromosomes can be present, as is the case in Down syndrome. Down syndrome is caused by an extra copy of chromosome 21. That is why it is sometimes called trisomy 21.
How is NIPT done?
The test is performed on a sample of the mother’s blood. About 10mls of blood is taken from the arm - just like a normal blood test. The blood is then sent to the laboratory for testing.
How safe is NIPT?
As it is a simple blood test, NIPT carries no significant risk to you or your baby.
When is NIPT done?
From 10 weeks of pregnancy. Studies have shown that by 10 weeks there is adequate foetal cell free DNA present in the mother’s blood to conduct the test. The test is not recommended before that period. Therefore, it is essential that you have had an ultrasound scan and know the duration of your pregnancy and whether you are having one baby, twins, or more.
If you have already had a scan early on in your pregnancy, then on the day of the test (from 10 weeks onwards), another scan will be performed to confirm foetal activity and heartbeat.
How accurate is NIPT?
NIPT for Down syndrome is more than 99% accurate. This means that the test detects more than 99 out of 100 cases of Down syndrome, so there is only a very small chance that the test will not detect an affected pregnancy.
There is also a small chance that the test will incorrectly show that the baby has Down syndrome when it does not. This is known as a false positive result.
Even though the test is highly accurate, there is still a very small chance (around 1 in 300) of an incorrect result. Therefore, if the result of your NIPT predicts that the baby has Down syndrome, you will be offered an invasive test to confirm the result.
What types of chromosomal abnormalities does NIPT detect?
* NIPT will detect the most frequent trisomies
A trisomy is caused by the presence of three copies of a chromosome instead of the regular two.
NIPT detects the following trisomies:
• Trisomy 21, or Down’s Syndrome, is the most common trisomy.
• Trisomy 18, or Edward’s Syndrome, has a high incidence of miscarriage or late foetal deaths
• Trisomy 13, or Patau's Syndrome, is related to a high incidence of miscarriage. This chromosomal abnormality has a high foetal mortality rate.
* Alterations in sex chromosomes
NIPT also detects alterations in the number of sex chromosomes, including:
• Turner Syndrome (45, X), the absence of an X chromosome in girls.
• Klinefelter’s Syndrome (47, XXY),- the presence of an extra copy of the X chromosome in boys.
* Microdeletions and other trisomies
NIPT offers the option to analyze small changes in chromosomes, known as microdeletions, as well as trisomies in chromosomes 16 and 9.
Few NIPTs can be performed after IVF treatment, including egg donation and is also suitable for twins.
How long does it take to get the results from NIPT?
Usually results will be available within five working days.
In a very small number of cases the laboratory may be unable to obtain your results. This might be because there was not enough of the baby’s DNA present in the blood sample to obtain a result. If this happens, then, the option of repeating NIPT will be explored.
What are the possible results?
• No aneuploidy detected
Your baby is very unlikely to have Down syndrome, Edward syndrome or Patau syndrome
• Aneuploidy detected
It is very likely that the baby is affected with Down syndrome, Edwards syndrome or Patau syndrome. You will be offered an invasive test (see below) to confirm this result. This is offered because very occasionally, in around 1 in 300 cases, NIPT may not accurately reflect the result in the baby.
• Inconclusive result
As this is a new test we occasionally get an inconclusive or ‘unclear’ result. If we cannot detect a clear result, we will inform you and offer you another NIPT test.
• Failed result
Occasionally we get a failed result, if this happens we will offer you a repeat NIPT test at no additional cost.
How does NIPT compare with other screening tests currently offered during pregnancy?
The traditional screening test offered during pregnancy, which consists of an ultrasound scan and a blood test (or in some cases only a blood test), is less accurate than NIPT. The traditional test detects 84-90% of babies with Down syndrome.
What happens if the NIPT result predicts the baby has Down, Edwards or Patau syndrome?
If the NIPT result shows the baby has one of these chromosomal problems, you will be offered an invasive test. Invasive tests give a more definitive ‘yes’ or ‘no’ result as to whether the baby has Down syndrome or other common trisomy.
There are two types of invasive tests:
Chorionic Villus Sampling (CVS) – this is usually performed between 11 and 13 weeks.
Amniocentesis – usually performed from 15 weeks of pregnancy.
Both procedures involve using a fine needle to collect a small sample of either the amniotic fluid that surrounds the baby (amniocentesis) or a small sample of cells from the placenta (CVS). These tests carry a small risk of miscarriage of 0.5% to 1% in the UK. This means that for every 200 women who have a CVS or amniocentesis, one or two of them will miscarry due to the test.
What else should I consider before taking this test?
Before making a decision about NIPT, you may want to take some time to consider the test and discuss it with your partner. Think about how you might feel about the test results and how important the information would be for you and your family. Some couples feel that they may not continue with the pregnancy if a chromosome disorder was found. Others would continue whatever the results but would like to know in advance in order to prepare for the arrival of their baby.
If you are unsure about anything, it can be helpful to discuss it with your healthcare professional. Where can I get further information and support?
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Tel: 00 44 (0)207 563 1234
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NIPTs in general reduces the need for invasive testing
(An example scenario involving 100,000 pregnancies showing the difference between screening tests)