'Transformational' DNA test for Down's syndrome developed

A new DNA test for chromosome disorders, including Down's syndrome, is being hailed as "transformational" for expectant mothers.

For the first time, DNA analysis can be incorporated into antenatal screening in a way that is significantly more accurate and safer than existing methods.

Antenatal "reflex DNA screening", which screens for Down's syndrome, Edwards syndrome and Patau syndrome, detected more affected pregnancies than the test it replaced, with far fewer false-positives, medical scientists at Queen Mary University of London (QMUL) found.

Mr Joseph Aquilina, consultant obstetrician at Barts Health NHS Trust who participated in the project, said: "The new reflex DNA approach is transformational. Not only is the screening method better than current practice, but I have more time to devote to other clinical needs, as do the nursing and midwifery staff involved."

The new method was implemented in five UK NHS maternity units, screening more than 22,000 women between April 2015 and August 2016, and continues to be in use.

At present, women are offered screening for disorders at 10-14 weeks of pregnancy which combines an ultrasound scan and a blood test. If it shows that the baby is at risk, the mother is offered an invasive diagnostic test which involves inserting a needle into her womb to collect samples of fluid surrounding the foetus or tissue from the placenta.

With the new method, women provided a blood sample at about 11 weeks of pregnancy. The sample was divided into two; one used for the conventional screening test and one held in reserve. The first sample was used to assess the women's risk of any of the three disorders. If, on the basis of that test, the risk of having an affected pregnancy was 1 in 800 or a higher risk, the other blood sample was automatically retrieved for a DNA test without having to recall the women to provide a fresh blood sample.

This avoided needlessly worrying the women by informing them that the DNA test was required because of their increased risk of an affected pregnancy.

Professor Sir Nicholas Wald, from QMUL's Wolfson Institute of Preventive Medicine, who led the project, said: "The reflex DNA approach has substantial benefits to the well-being of the women screened.

"Not only are more affected pregnancies identified, but many fewer women will be made acutely anxious by being notified that they have a positive screening result."

The findings are published in the journal Genetics in Medicine.