For many years the goal of researchers has been to develop a diagnostic prenatal test for Down's syndrome that does not involve an invasive procedure with an accompanying risk of miscarriage. The most recent breakthroughs have involved analysing cell-free maternal and fetal DNA in the mother's blood. This has come to be known as 'non-invasive prenatal testing' (NIPT), because all that is needed is a maternal blood test.
Although NIPT for Down's syndrome is not diagnostic, large scale studies show that the test has a detection rate of over 99%. So it is currently a very sensitive screening test for Down's syndrome, and can also look for Edwards' and Patau's syndrome.
NIPT is not yet available on the NHS except in a small number of hospitals as part of either a research study or pilot project. An evaluation study was completed last year by Professor Lyn Chitty and her RAPID (Reliable Accurate Prenatal non-Invasive Diagnosis) project team. The team set out to provide information on how it might be implemented into the NHS in a fair and affordable way. Prof Chitty reported their findings to the UK National Screening Committee in June 2015. After a detailed review of the evidence and a public consultation, the UKNSC has recommended a staged implementation into the NHS. This has yet to be agreed by Government Ministers. In the meantime, NIPT is widely available in the private sector.
Individual clinicians and private clinics are offering NIPT provided by a number of different laboratories, based here and overseas. There is no ‘direct to consumer’ testing available; it must be done via a health care professional. You can find out more about the labs doing the analysis below. They all claim high detection rates but some differ in the way they analyse the cell free fetal DNA. One way to check their claims is to look at the published data* they have on their test performance. You should be able to find this on their websites.
NIPT can be performed from 10 weeks of pregnancy. Before this it is difficult to collect enough cell-free fetal DNA (cffDNA) from the blood sample. Even after 10 weeks there is a chance that they will not be able to collect enough cffDNA to provide a result. This can happen in about 3% of cases. Women who are significantly overweight have been found to be at higher risk of being in this 3%. Most providers will do a second test for free if this happens.
Results usually take 10 days to two weeks to come back from the laboratory. Remember NIPT does not give a yes/no answer for Down’s syndrome. If the result is reported as 'low risk' or very unlikely to be affected’, it is extremely unlikely that the baby has the condition. If the test result given is 'high risk' or ‘likely to be affected’ you will be offered a CVS or amniocentesis to give a definite diagnosis. It is important to realise that in this case the CVS or amniocentesis will most often confirm that the baby has Down's syndrome.
Our research suggests that costs for NIPT range from £400 to £900. If a provider is charging significantly more than £500, ask what the fee includes. Most clinics will include an ultrasound scan in the cost. If you are interested in having the test at a private clinic, make sure you check that they have a clear link with an NHS unit, so that there is a co-ordinated care pathway in place if you were to have a worrying test result.
Most private providers offer NIPT for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome (which are two very severe chromosomal disorders). There is lots of published evidence that NIPT can produce a very accurate result for these conditions.
Some private clinics are offering NIPT for other conditions and even ‘micro deletions’ (when small pieces of genetic information are missing). We would advise you to think very carefully before agreeing to be tested for other conditions. The evidence is not so clear on how good NIPT is for these and sometimes you might be given information that leads to great uncertainty. Please feel able to call us on the helpline to talk this through or get expert advice from a clinical geneticist or genetic counsellor.
*to be of the highest quality, test performance data should be published in a peer reviewed scientific journal and should report pregnancy outcomes from studies involving 1000s of women.
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