The British Journal this week reported that the NHS is one step closer to offering pregnant women who have an increased chance of having a baby with Down's syndrome a new test to detect the condition.
What is Down's?
Down's syndrome is a genetic condition that occurs when there is an extra copy of chromosome 21. Chromosomes contain the genes for development, and there are 23 pairs in each cell. The extra copy usually leads to certain characteristic physical features and some learning disabilities. People with Down's syndrome can find it harder to communicate or grasp new concepts, and can often have additional health problems. Around 775 babies are born with the condition each year in England and Wales.
Current tests
Currently, all women are offered screening for Down's syndrome:
- a combined test between 11-14 weeks of pregnancy, which is a blood test and a nuchal scan
- a quadruple blood test between 14 – 20 weeks
If either of the screening test results show a higher risk of having a baby with Down's, women are offered further diagnostic tests:
- a chorionic villus sampling (CVS) test, where a sample of the placenta is removed with a needle for further examination, from week 11 onwards; or
- an amniocentesis, where a sample of the amniotic fluid which surrounds the baby in the womb is extracted with a needle, from approximately week 15 onwards.
Both tests are reported to have a 1 in 100 chance of increasing the risk of miscarriage.
The new test
The new screening test being trialled is a blood test known as non-invasive pre-natal testing. It works by screening some of the baby's genetic profile from the mother's blood sample. The theory behind this is that some parts of a baby's DNA are interspersed with the mother's blood, and so any anomalies within the DNA can be picked up. Such a test would mean fewer women would need to undergo an amniocentesis test, which is more invasive and carries a higher risk of miscarriage and serious infection.
Studies have shown the NIPT to be 99% accurate in detecting Down's syndrome following a successful trial involving over 10,000 women in October 2015, and it has recently been approved by the UK National Screening Committee. It is currently awaiting final approval from the government before it can be introduced on the NHS.
Arti Shah, Associate at Fieldfisher, commented:
“It is always interesting to read about new scientific discoveries being made to improve health, and if a blood test can be used instead of a more invasive test such as amniocentesis, it will no doubt provide greater reassurance to expectant mothers.”
Sources:
Screening for Down's syndrome, Edwards' syndrome and Patau's syndrome - NHS (www.nhs.uk)