Researchers found 98% of Down’s syndrome cases could be detected by A new non-invasive blood test

A new non-invasive blood test which can reliably detect whether or not an unborn baby has Down’s syndrome during the first trimester of pregnancy is to go on trial at two hospitals next month.

The test, which analyses a baby’s DNA present in its mother’s blood, could be an improvement on current screening methods, according to researchers.
Down’s syndrome, and other chromosomal disorders characterised by an additional chromosome, is currently tested for between the 11th and 13th weeks of a pregnancy, using an ultrasound screen and a hormonal analysis of the pregnant woman’s blood.
Those deemed at high risk of carrying a baby with such a disorder are then given a definitive test involving chorionic villus sampling and amniocentesis.
But this is invasive and carries a risk of miscarriage.
A study carried out at the Harris Birthright Centre at King’s College London is the first to look at the feasibility of screening for the chromosomal disorders – known as trisomies – using foetal cell free DNA (cfDNA) from a pregnant woman’s blood.
The tests, carried out at the 10-week stage on 1,005 pregnancies, were found to be more sensitive at detecting Down’s syndrome and returned fewer ‘false positive’ results than the initial combined tests usually carried out between the 11th and 13th weeks.
Researchers found that up to 98 per cent of cases of Down’s syndrome could be detected.
Invasive testing was then needed for confirmation in less than 0.5 per cent of cases.
The test costs £400 so will not be offered across the NHS at this stage, but it will initially be offered free of charge on a trial basis at two hospitals – Kings College Hospital in London and Medway Maritime Hospital in Kent.
The authors of the study, published in the Ultrasound in Obstetrics & Gynecology journal, 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.’
The authors added: ‘Screening by cfDNA testing contingent on the results of an expanded combined test would retain the advantages of the current method of screening, but with a simultaneous major increase in detection rate and decrease in the rate of invasive testing.’