Down’s syndrome screening at Beard Mill Clinic
using the Harmony™ Prenatal Test
The Harmony™ Prenatal Test is a new “non-invasive” prenatal test (NIPT) to screen for Down’s syndrome.
What is Down’s syndrome?
It is very important to remember that most babies are born without any problems, but about 1 in every 700 babies will have Down’s syndrome. This is a genetic condition. Our DNA, a complex chemical that codes our genetic information, determines all the characteristics that makes us who we are. Sections of DNA are packed together to make a gene and several thousand genes are then coiled up to make up a chromosome. Every cell in our body has 46 of these chromosomes, 23 coming from our mother and 23 from our father. A person with Down’s syndrome has 47 chromosomes instead; they have an extra copy of chromosome 21 and this causes a genetic imbalance that leads to a variable amount of both physical disabilities and learning difficulties. Nothing you do can cause it or prevent it. It is just something that happens at conception and potentially anyone could have an affected baby, but it is more common in older mothers.
Why do we screen for Down’s syndrome?
Over the last few years, there have been lots of advances in how to screen for Down’s syndrome. In most cases the tests will reassure you that it very unlikely that your baby is affected, but just occasionally the test may indicate you are at high-risk, although it is important to remember that this still doesn’t mean that the baby has Down’s syndrome.
For some parents knowing that their baby has Down’s syndrome wouldn’t affect their decision to continue with the pregnancy, but it allows them the opportunity to plan and learn more about the condition before their baby is born. However other parents would choose not to continue with the pregnancy. It is a very personal decision, and a very difficult one. The medical team looking after you will give you as much information and support as you need to help you decide what to do. But before doing this you need to be absolutely sure that the baby is affected through an “invasive test”.
These invasive tests do give you a definite answer as to whether your baby is affected or not, but they involve taking a sample of tissue directly from the placenta (chorionic villus sampling or CVS) or a small amount of fluid from around the baby (an amniocentesis) and both of these tests can cause a miscarriage, even if the baby is healthy. This happens rarely, but often enough to mean that they should only be done if there is a high suspicion that the baby may have a problem.
Until recently the best test to assess whether you are at high-risk of having a baby with Down’s syndrome has been the combined first trimester screening test, sometimes known as the nuchal scan or the 11-1 4 week scan. Babies with Down’s syndrome will often have more fluid at the back of the their neck (an increased nuchal translucency measurement); a flatter facial profile with an absent or small nasal bone; abnormal flow of blood around their heart and through the liver; and a different amount of two placental hormones that can be measured in the mother’s blood. None of these markers will tell you that the baby definitely does or doesn’t have Down’s syndrome, but most affected babies will have one or more of these features and looking at all these markers will identify about 95% of affected babies as being at high-risk. Of course this means that 5% of affected babies will be given a low-risk result and may go undetected (a false negative result). Furthermore about 3% of normal babies will be given a high-risk result. The majority of parents with a high-risk result will choose to have an invasive test to make a definite diagnosis and most of these will subsequently find that the baby is unaffected (a false positive result).
The new test, the HarmonyTM Prenatal Test, significantly improves this situation, identifying over 99% of the affected babies as high-risk, but reporting less than 1% of normal babies as high-risk.
How does the Harmony™ Prenatal Test work?
As the baby develops, a small amount of the baby’s genetic information (cell-free DNA) passes into the mother’s blood. New genetic sequencing techniques mean that this DNA can now be analysed to identify if there is too much chromosome 21 – the extra chromosome found in Down’s syndrome.
It won’t give a definite yes / no answer, but the research to date has been promising, showing that over 99% of affected babies will be identified as high-risk, but very few normal babies will be given a high-risk result.
However it must be stressed that the test is not diagnostic and that a low-risk result does not mean that there is absolutely no risk and a high-risk result will still need an invasive test to provide certainty.
What else does the Harmony™ Prenatal Test pick up?
The Harmony™ Prenatal Test has been developed specifically as a screening test for Down’s syndrome. However the same genetic sequencing techniques can be used to look at two additional chromosomes – chromosome 18 and chromosome 13.
Just as babies with Down’s syndrome have an extra chromosome 21, babies with Edwards’ syndrome have an extra chromosome 18 and babies with Patau’s syndrome have an extra chromosome 13. However the abnormalities that babies with Edwards’ syndrome and Patau’s syndrome have are so severe that sadly these babies miscarry, are stillborn, or die shortly after birth.
The Harmony™ Prenatal Test will look at the risk of Edwards’ and Patau’s syndrome too, although the results so far suggest that the pick up rates aren’t quite so good as the Down’s syndrome detection rates (98% for Edwards’ syndrome and 80% for Patau’s syndrome), but these babies usually have abnormalities that can be seen on ultrasound scan, so certain ultrasound features should always heighten suspicion, regardless of a normal Harmony™ Prenatal Test.
Do I still need to have a scan as well as the Harmony™ Prenatal Test?
Yes. The Harmony™ Prenatal Test cannot be used in multiple pregnancies, so it is important to have a scan first to check that you are not having twins. But a good 12-week scan will also pick up a significant number of structural abnormalities, such as spina bifida, and an increased nuchal translucency measurement is a strong marker for a wide range of conditions other than Down’s syndrome. It is therefore essential that the Harmony™ Prenatal Test results are always looked at in the context of the 12-week scan findings and never in isolation.
A nuchal translucency measurement of more than 3.5mm is particularly worrying and is more common in babies who have some of the rarer and more unusual genetic abnormalities that will not be picked up by the Harmony™ Prenatal Test. Parents may consider having an invasive test, regardless of the Harmony™ Prenatal Test result, if the nuchal translucency measurement is above 3.5mm or there are other serious structural abnormalities. This will affect only a very small number of patients.
It is also very important to have the 20-week anomaly scan to look for any structural anomalies that may not be obvious at the 12-week stage.
How is the Harmony™ Prenatal Test done?
The Harmony™ Prenatal Test involves taking two tubes of the mother’s blood from a vein in her arm, in exactly the same way that a normal blood test is done. Other than a small amount of discomfort and possible bruising, there are no risks to the mother and absolutely no risk of harm to the baby. The sample is then sent to a laboratory in the USA, Ariosa Diagnostics Inc, who will extract cell-free DNA from the blood and carry out the Harmony™ Prenatal Test.
The results are sent back to Beard Mill Clinic within two weeks.
When should I have the Harmony™ Prenatal Test done?
The Harmony™ Prenatal Test can be done anytime from 10 weeks onwards, right up until the end of the pregnancy.
There will be some parents who make the decision early on that they definitely want to have the test done. These ladies will be seen at Beard Mill Clinic at 10 weeks to have a quick scan to confirm dating and check that there is definitely only one baby. At this visit, three tubes of blood will be taken – one for the biochemical markers that are routinely looked at as part of the first trimester screening test and then two special tubes to be sent to the USA for the Harmony™ Prenatal Test.
A second visit would then be scheduled for 2 weeks later, to perform a detailed 12-week scan, looking at the structure of the baby and any ultrasound markers of an abnormality. The results of the Harmony™ Prenatal Test will be available at that point so will be fully explained to the parents and any necessary follow-up arrangements made.
Some parents may prefer to have the usual combined first trimester screening test (the nuchal scan) and only decide to have the Harmony™ Prenatal Test if they are found to be at high-risk, or aren’t completely reassured by their risk and want a more accurate test, but without taking any of the risk associated with an invasive test. These ladies will have their usual first trimester screening at Beard Mill Clinic and will be given sufficient time and information to help them decide if the Harmony™ Prenatal Test is really the right thing for them to do.
Can anyone have the Harmony™ Prenatal Test?
The Harmony™ Prenatal Test is only available at a few private clinics in the UK, but any parents can choose to have the test and can contact Beard Mill Clinic directly. A referral from your GP is not required.
It can be performed in all single and twin pregnancies, including those conceived by IVF.
In 5% of cases the analysis of the sample fails because insufficient cell-free DNA is extracted. In this situation, the mother will be asked to provide a second blood sample at no additional cost.
How much does the Harmony™ Prenatal Test cost?
At Beard Mill Clinic the test is only offered as a package of first trimester screening if booking before 14 weeks. This includes:
- A dating scan at 10 weeks (if booking before 10 weeks)
- The blood test for the two first trimester biochemical markers
- The Harmony™ Prenatal Test
- A detailed 12-week scan
- Pre-test counseling and a full explanation of the results
The cost of this package is £500.
After 14 weeks the cost is the same, but the 12-week scan and biochemical markers are replaced by a detailed anomaly scan.