This month I’m going to be talking about a relatively new type of prenatal testing/screening that is available in the UK on a private basis. It’s something that has only been on my radar for about a year, and I initially heard about it through a friend who chose to have this type of screening test for her baby, rather than through my work as a doctor, so I’d be really interested to hear if many of you are aware that these tests are available, or if you’ve had them done during your pregnancy.
Non-invasive prenatal testing (NIPT) is a screening test for common genetic conditions, including Down’s syndrome, Edward’s syndrome and Patau’s syndrome, and also some sex chromosome abnormalities such as Turner’s syndrome and Klinefelter syndrome. The tests can also determine the sex of your baby, but of course you can opt out of this if you have chosen to keep it a surprise. In addition to these chromosome abnormalities, you can choose to have additional genetic testing for five different syndromes that are caused by microdeletions (where a small piece of a chromosome is missing). NIPT can be done as early as 9-10 weeks into your pregnancy, and is performed simply by taking a maternal blood sample, which is sent off to the laboratory for analysis, with results sent to you between 5 and 10 days later.
How does NIPT work?
During pregnancy, fragments of your baby’s DNA enter your blood stream. These screening tests are able to analyse that cell-free DNA and assess the chance that your baby has one of the chromosomal abnormalities that are being tested for. A simple way of thinking about this that I use is, for example, if they analyse your blood sample and find Y chromosomes within it, it’s pretty certain that you must be carrying a male baby — although I’m sure that the process is far more complicated than that!
How reliable is NIPT?
The results are given in terms of a chance of having an individual abnormality – either low or high risk. The detection rate is slightly different for the different syndromes, but is more reliable than the traditional first trimester screening test offered on the NHS. For Down’s syndrome, the detection rate (true positive result) for NIPT is greater than 99%, and the false positive rate (results show a ‘high risk’ when the baby does not actually have Down’s syndrome) for NIPT is less than 0.1%.
How does this compare to the NHS first trimester screening programme?
At present, the NHS first trimester screening that all women are offered is called the triple test, consisting of a blood test and a measurement of the fluid at the back of the baby’s neck, called nuchal translucency. Results are also given in the form of low or high risk, but with the triple test, you will also be given an estimate of that risk, e.g. ‘low risk – 1/64,000’.
For Down’s syndrome, the detection rate for the NHS first trimester screening is around 79%, meaning that about 20 out of 100 babies born with Down’s syndrome, where all 100 mothers had the NHS first trimester screening, will have been given a ‘low risk’ result. This sounds alarming, but this is not actually the case in reality, as the NHS screening test classes anything greater than 1 in 150 as a ‘high risk’, and those mothers will be offered further testing, in order to increase the detection rate for Down’s syndrome. For Down’s syndrome, the false positive rate for the NHS first trimester screening it is 3-5% (again, for the reason stated above, this figure is actually higher, meaning that if you get a ‘high risk’ result on the NHS screening test, your chances of having a baby with Down’s syndrome are actually very low.
If you are given a ‘high risk’ result following either NIPT or NHS first trimester screening, you should be counselled on your options and offered one of the following:
Chorionic villus sampling (CVS)
This is where a few cells from the placenta are collected using a needle through the tummy. It can be carried out between 11 and 14 weeks of pregnancy. CVS does carry a risk of miscarriage of around 0.5-1%.
This is where a sample of amniotic fluid is collected using a needle through the tummy. It can be carried out between 15 and 20 weeks of pregnancy. This also carries a risk of miscarriage of around 0.5-1%.
Detailed foetal anomaly scan at 20 weeks
You may decide to not have any invasive testing, but will be offered a detailed scan at 20 weeks, which may be performed by an obstetrician rather than an ultrasonographer. Around 50% of babies with Down syndrome may have a structural abnormality that can be picked up at this scan, for example a heart defect. If the scan is completely normal, it does not rule out a chromosomal abnormality, but it may offer reassurance that there are no serious physical defects.
If you have decided that you would continue with the pregnancy regardless of the results of testing, you may choose not to have any further tests.
How much does NIPT cost?
There are a few different providers of NIPT in the UK, the ones that I am aware of being Harmony, Serenity, Panorama, Nifty and Verify; with the most widely available one being Harmony. Prices start at around £400 for the basic chromosomal abnormality tests and an ultrasound scan to confirm that you are far along enough in your pregnancy to take the test, and whether you are carrying one or more babies. To find out if any of the NIPT options are available near you, I’d suggest googling to see if there are any local private clinics which offer it.
Should NIPT be available on the NHS?
Whilst I don’t want to open a can of worms, I anticipate that a few of you may be thinking this: if it’s a ‘better’ test than the current NHS pre-natal screening, is it ethical for it to only be available to those who can afford it? I’m going to be completely honest and say that I simply don’t know enough about it to comment further; what I do know is that the current NHS antenatal care is excellent and fulfils its purpose, and also that (pure speculation) I wonder if, in the future, as more providers offer NIPT, the (currently prohibitive) cost of the service will be driven down, making it more affordable for both the individual, and for the NHS.
Understanding Non Invasive Prenatal Testing
I should mention that whilst this post is about a non-NHS service, it has been written purely for information, and is not sponsored or affiliated in any way by any providers of NIPT (none of my posts for Rock My Family carry any conflict of interest, and I promise to be completely honest if they do!)
Do you have any experience of pre-natal testing? Were you aware that NIPT was available in the UK? I’d love to hear if you found this at all helpful. I’d also like to offer an apology of the very slow responses to comments on last month’s post; I was on holiday with Ben and Oscar, but am back to normal service this month!