Illumina Blood Test for Downs Syndrome Screening
What is the Illumina test?
The Illumina test is a screening test, not a diagnostic test, which helps you to find out the chance that your baby has Down syndrome. The test analyses cell free DNA in maternal blood and gives a strong indication of whether the baby has a high chance of having trisomy 21 (Down syndrome), trisomy 18 (Edward’s syndrome) or trisomy 13 (Patau syndrome).
The test identifies 99% but not all of the babies with trisomy 21, 97% of babies with trisomy 18 and 94% of babies with trisomy 13
In humans, most people have 23 pairs of chromosomes (a total of 46 chromosomes). In trisomy, there are three rather than two of a particular chromosome total 47 chromosomes. The most common trisomies present in the first trimester of pregnancy are of chromosomes 21, 18 and 13.
Trisomy 21 (Down syndrome) is found in about 1 in 700 births and the risk increases with maternal age. The condition is associated with intellectual difficulties, and some physical defects – most commonly heart abnormalities. The life expectancy is about 60 years. Down syndrome is a variable condition and many families report high satisfaction with life.
Down’s syndrome Association
Tel: 020 8682 4001
Trisomy 18 – Edwards syndrome – (1 in 3500 births) and trisomy 13 – Patau syndrome – (1 in 5000 births) risk increases with maternal age. The conditions are associated with severe mental handicap and severe physical defects. Most affected babies die before or soon after birth and rarely survive more than the first year of life.
Supporting organisation for Trisomy 13 and Trisomy 18 (SOFT) UK
Why you need a scan before you have the Illumina Test
It is important that an ultrasound scan is performed just before the blood test to confirm the pregnancy, check the baby is alive and how old it is and to check whether there are twins or more babies.
Who is not suitable for a Illumina Test?
Women who have the following are not suitable for NIPT testing:
- A history of active malignancy
- A pregnancy where the baby has died
- A pregnancy which started as twins and one twin did not develop – sometimes known as vanishing twin
- A pregnancy with more than 2 babies
- A history of bone marrow or organ transplant
- Rare maternal biological conditions may affect the accuracy of the test
- Maternal Aneuploidy
I have twins – what information can the Illumina Test tell me?
|Can have with twin pregnancy?||Yes|
|Can have with twin pregnancy with one twin demised?||No|
|Can have with twin pregnancy when an empty sac is seen?||No|
|Can have with IVF when two embryos are transferred and one is viable?||Yes, provided only one implanted|
|Can I find out the gender of my twins if:|
|Both are boys?||Only one|
|Both are girls?||Yes|
|Boy and a girl?||Only one male|
|If high probablity result for:|
|Male twins||Applies to one or both males|
|Femaile twins||Applies to both females|
Who needs the Illumina Test?
Anyone who is anxious about her baby having a condition such as Down, Edward’s or Patau syndrome can have it. It is predicted that in 10 years it will become available for all on the NHS. Women who may need it are those that are older (particularly over 40 years), have already had a chromosomally abnormal pregnancy or who are at particular risk of miscarriage should they have an amniocentesis or chorionic villous sample.
If you decide to go ahead with NIPT, you must be aware that NIPT may lead to some difficult decisions in the event of a high chance result, such as whether to have diagnostic testing and, if the diagnosis is positive, whether to continue the pregnancy or have a termination.
Antenatal results and choices (ARC)
Tel: 020 7631 0285
We can help you through this process and put you in touch with organisations to support you.
We can arrange diagnostic testing for you privately or refer you to the screening co-ordinators at your NHS hospital.
How is the test done?
- The mother has to read and sign a consent form and sign a form for data release.
- An ultrasound scan is usually done first to check the baby is alive and date the pregnancy and check for twins. This can be done from 10 weeks gestation and up to the end of the pregnancy.
- This is a simple blood test from the vein in the woman’s arm like any other blood test. There is no risk from having the test.
- One tube needs to be fully filled.
- The tube is immediately packaged and couriered to the Laboratory in London.
How long does it take to get a result?
The results from the blood test are usually available in 2-4 working days and we will notify you as soon as they are available by telephone/email or letter.
In about 4% of cases, the test does not give a result. This does not mean there is a problem with the baby but is due to a technical difficulty. If you would like the test can be repeated at no extra cost – there is a 65% chance that the test will give a result.
How is the result expressed?
If the results show that there is a high chance that the baby has trisomy 21, 18 or 13, it does not mean that the baby definitely has one of these conditions. The test can be falsely positive in around 20% of cases for trisomy 21 (Positive predictive value of 80.9%). The PPV is lower for trisomy 13 and 18.
Studies show that the test is more accurate in women with a high chance of having a baby with Down syndrome.
Another test would be needed to confirm a more definite diagnosis – these tests are invasive and carry a small (< 1%) chance of miscarriage. Further testing is entirely up to the woman. Referral on to hospital department to discuss further testing can be made by us.
If the test shows a low chance (less than 1 in 10,000, that the baby has trisomy 21, 18 or 13, then it is unlikely that the baby has one of these conditions.
How much does it cost?
The test is currently £495 including the dating ultrasound scan up to 10 weeks. On some occasions we can use a previous written scan report, in which case the cost of the Illumina blood test would be £395. However it is our discretion as to whether we can use the written scan report you provide – a picture of you baby is not acceptable. If you need a scan at a later stage in the pregnancy the cost will depend on how far pregnant you are.
Illumina Test – NIPT for other conditions
Sex chromosome aneuploidy (sca)
Recommendations from ARC (Antenatal Results and Choices)
There are now a number of biotech companies and laboratories offering NIPT in the UK. While all will include a screening result for Downs syndrome, Edwards’ syndrome and Patau’s syndrome (also known as trisomies), many will also screen for sex chromosome anomalies (e.g. Turner’s syndrome, Triple X etc.). Some tests include results for other genetic conditions that are the result of a deletion or duplication of genetic material on a chromosome.
There is now enough good evidence to make us confident that NIPT is the most accurate screening test we have for Downs syndrome, Edwards’ syndrome and Patau’s syndrome. However, there is less in the literature about other conditions. So we suggest restricting use of NIPT to the main trisomies, unless advised otherwise by your genetics specialist.
Tel: 020 7631 0285
Do I need to have any other tests?
The Illumina Blood Test, done before the 11 – 14 week scan, does not replace the Combined Test as you still need the 12 week nuchal translucency (NT) and nasal bone scan and to check for structural abnormalities. You will also need a detailed abnormality scan between 19 – 21 weeks
- The Illumina test does not provide information on other rare chromosomal abnormalities. If the scan at 11-13 weeks shows a high nuchal translucency (more than 3.5 mm) or major defects, such as exomphalos, holoprosencephaly, heart abnormalities or megacystis, the risk for some rare chromosomal defects may be high. In such cases you may choose to have CVS or amnio.
- The Illumina test does not provide information on physical defects, such as heart or brain abnormalities and spina bifida, or the babys growth. It is therefore advisable that you still have ultrasound scans at 11-13 weeks and at 20-22 weeks to examine the baby’s anatomy and at 30-32 weeks to examine the baby’s growth.
When can I have the Illumina Test?
You can have the Illumina blood test and scan from 10 weeks. If you want both the Combined Test and Illumina Test at the same time then this needs to be done at 12 weeks. However, some people decide to have the Combined Test first and then proceed to the Illumina blood test if the Combined Test result is not as reassuring as they would like.
We recommend having the Illumina Test at 10 weeks +/- a scan – this depends on whether you can provide a written report of a previous scan you have had done and that we verify this has the correct information that we need. If not, we will need to do a dating scan for you as we need to know exactly how many weeks pregnant you are, check the baby is alive and check whether you are expecting twins.
High risk Combined Test and/or nuchal translucency of over 3.5mm:
If the scan at 11-13 weeks shows a high nuchal translucency (more than 3.5 mm) or major defects, such as exomphalos, holoprosencephaly, heart abnormalities or megacystis, the risk for some rare chromosomal defects may be high. In such cases you may choose to have CVS or amnio.
Those who are very high chance for Down, Edward’s and Patau syndrome may decide to proceed to an invasive procedure such as a CVS (Chorion Villus Sample) or if the chance is borderline you may decide then to have the Illumina Test as this carries no risk to the baby.
It is very important to get correct counselling so that you know which test is both appropriate and best for you.
We always recommend you discuss the Illumina Test report with your midwife and/or hospital Consultant.
The Illumina Test can also reveal the sex of the baby. We therefore will need to know whether this is something you wish to find out. If not, we can issue a report without the sex of the baby on it.
Further information about the Illumina test
PDFs – click to download:
Illumina Test Information leaflet for patients
(incudes information on Sex chromosome aneuploidy (sca) and Monosomy X eg. Turners syndomre and Triple X etc)
(T21, T18, T13)
|82%||1 in 26|
|NIPT||>99%||<1 in 1,000|
* Proportion of fetuses with trisomy correctly identified by the test
as high probability of disorder.
# Proportion of normal fetuses incorrectly identified by the test
as high probability of disorder.
NIPT Performance data
in a general screening population
The Warwick Evidence Systematic Review of the performance of NIPT found that the negative predictive value of NIPT was 99.9%. What does that mean? The negative predictive value (NPV) tells you how likely it is that a low probability NIPT result is correct.
So, if you get a result that shows a low probability of the conditions screened for: you can be pretty certain you do not have a fetus with any of the conditions.
In the event of NIPT results showing a high probability of the conditions screened for: the positive predictive value (PPV) varies for each condition from 81.6% for Down’s Syndrome, 49% for Patau’s Syndrome, and 37% for Edwards’ Syndrome. A high probability result does not definitively confirm the presence of one of the conditions and further testing is required.
There may be some factors which cause an inconclusive result (See Further Reading below) and a further invasive test may be required for accurate determination.
NIPT tests are extremely accurate in the detection of pregnancies where there is a high probability of Downs’ Syndrome, Patau’s Syndrome or Edwards’ syndrome.
- Up to 99% detection rate for Down’s Syndrome (Trisomy 21)
- Up to 97% detection rate for Edwards Syndrome (Trisomy 18)
- Up to 94% detection rate for Patau’s Syndrome (Trisomy 13)
What does that mean in real terms? The NIPT test will detect 99% of pregnancies where a high probability of Down’s Syndrome is present.
The NIPT is more accurate than the first trimester combined test or second trimester quadruple test for estimating the chance or risk that the baby has Down’s syndrome. The false positive rate for all trisomies is <0.1%. Conventional screening tests can miss 15% or more of trisomy 21 cases.
More information on the Warwick Evidence Systematic Review can be found here.
A microdeletion is the absence of a small piece of chromosome and is named by the area of the chromosome that is absent. The Illumina test can, for an additional cost, look for 22q11.2microdeletion, the most common genetic cause of intellectual disability and heart defects after Down syndrome. However, currently due to a lack of research into the reliability of this test Ultrasound Direct are not offering this as an additional option at this present time.