What You Need To Know About The ‘New’ test for Down’s Syndrome
Firstly, it’s not new. The ‘new test’ for Down’s Syndrome is a type of non-invasive prenatal test (NIPT). The test is performed by taking a small blood sample from the mum and identifying tiny fragments of baby’s DNA in her bloodstream which have crossed over the placenta. It can be used to test for several serious genetic conditions including Down’s Syndrome. The test has been available in many private clinics for several years. It is known by several different brand names depending on which laboratory performs the test. This month the UK National Screening Committee has recommended that it be offered to ‘high risk’ women within the NHS. Some hospitals have already adopted this strategy, but uptake varies and it is not yet universally available in the NHS.
The test is popular for two main reasons. Until now the most common standard practice in the NHS has been to offer all women ‘combined screening’ by way of a scan at around 12 weeks of pregnancy and a blood test. The results are given as a ‘risk’, for example your baby has a 1 in 100 chance of having Down’s Syndrome. A cut-off of 1 in 150 is used as classifying women as ‘high-risk’, they are then offered more accurate invasive testing. These invasive tests, called chorionic villous sampling and amniocentesis, unfortunately carry a risk of causing miscarriage, about 1 in 100.
The risk of miscarrying a healthy baby versus wishing to gain more information about their unborn baby is a very difficult decision.
Non-invasive prenatal tests do no carry any risk of miscarriage as they are a simple blood test taken from the mother. The blood test usually costs around £400 privately, it can be done from 10 weeks of pregnancy and results can be received in less than 1 week.
The test is not only safer but more accurate too. The current standard ‘combined’ ultrasound and blood test screening detects about 80 to 90% of babies with Downs Syndrome. So a significant number of mums carrying babies with Down’s Syndrome are given false reassurance at present. The new NIPT is more accurate detecting 98 to 99% of babies with Down’s Syndrome. False alarms given by the test are also thankfully rare occurring in only 0.3% of cases or 3 in 1000.
NIPT is not a complete replacement for the usual 12 week ultrasound scan, at your scan appointment the sonographer will also perform many other checks on baby’s development.
Deciding which test is right for you is a difficult decision. I would encourage all women to make sure they understand the ‘numbers’ involved. For some women being prepared with the most possible information is the right choice other may feel more comfortable without undergoing checks for genetic abnormalities. Testing is full of moral and ethical dilemmas but only you know what is right for your pregnancy.
I wouldn’t feel comfortable finishing this blog without saying that Down’s Syndrome is a genetic condition which can have serious health consequences for a baby but these babies can also have long, happy, healthy, fulfilling lives. Please make sure you get all the information and support you need, discuss your options with your midwife or doctor and those closest to you. I would also point to Antenatal Results and Choices, which is an excellent charity offering unbiased information and support to women and families.
Dr Lucy Hooper