Researchers from the Harris Birthright Research Centre for foetal medicine at Kings College London have developed a blood test which analyses foetal cell free DNA (cfDNA) in maternal blood to test whether the child is affected by Downs Syndrome or not.
In the initial tests 1,005 pregnant women were tested at the ten-week stage and researchers found that the test provided a result that showed either a 99 per cent chance of having Down Syndrome or a less than one in 10,000 chance.
Next month, the research team will begin a two-year prospective study of 20,000 women to further assess the test at Kings College Hospital and Medway Maritime Hospital in Chatham, Kent.
Professor Kypros Nicolaides, the chief researcher, said, ‘This study has shown that the main advantage of cfDNA testing, compared with the combined test, is the substantial reduction in false positive rate.
'Another major advantage of cfDNA testing is the reporting of results as very high or very low risk, which makes it easier for parents to decide in favour of or against invasive testing.’
Women are usually tested between weeks 11-13 of pregnancy with an ultrasound during which the pocket of fluid at the back of a baby’s neck is measured. Babies with Down syndrome tend to have more fluid than normal.
The mother may also have blood tests to check levels of certain hormones. They are then given an estimation of the chances of their child having Down Syndrome. Those with a higher estimated risk can have one of two invasive tests, which have a one in 100 risk of miscarriage. These are either a chorionic villus sampling, which involves the testing of a small sample of placenta or an amniocentesis, which tests the amniotic fluid around the baby.
The new blood test currently costs around £400 and the conventional test costs £180 for all pregnant women.
Carol Boys, chief executive of the Down Syndrome Association, said, ’The latest results from Professor Nicolaides and his team at King’s College show that the use of an early non-invasive blood test that could be used throughout the national screening programme is still a fair way off.
‘The test is becoming more accurate. There are still small but significant anomalies that make it difficult to see how this could replace the current screening process. For pregnant women, this test has become an additional option, and the screening period has been extended by a further two weeks. Invasive procedures are still required to confirm results.’
Around 750 babies are born with Down syndrome each year in the UK. The condition is caused by the presence of an extra copy of chromosome 21, which occurs by chance.
- The research was published in Ultrasound in Obstetrics in Gynaecology and can be found here.