Maternal blood test for Down's syndrome to be trialled in UK

A new method for prenatal testing for Down's syndrome will be tried out at Great Ormond Street Hospital for Children (GOSH), London.

The maternal blood test will look for fragments of DNA from the placenta and the fetus in the mother's bloodstream through a simple blood test (reported in BioNews 708). The study will help determine whether this form of non-invasive prenatal testing (NIPT), which is already offered privately, should be offered to pregnant women in the NHS.

'At present, pregnant women who are shown to be at a higher risk of having a baby with Down's syndrome are offered invasive follow-up tests which carry a risk of miscarriage', said Lyn Chitty, professor of genetics and fetal medicine at GOSH and lead investigator. 'It is hoped that the introduction of NIPT will reduce the number of these invasive tests, while detecting more cases of Down's syndrome than we currently do'.

Down's syndrome occurs as a result of an extra copy of chromosome 21 and affects around one in every 1,000 babies born.

At present, the screening tests offered for Down's syndrome involve a combination of an ultrasound scan of the fetus and a blood test for the mother. Those found to be at higher risk are offered invasive follow-up tests, such as CVS (chorionic villus sampling) or amniocentesis, which both carry a low risk of miscarriage. The BBC reports that those who test positive using NIPT will then be offered an invasive procedure to confirm the result.

Dr Anne Mackie, from the UK National Screening Committee, added that 'early indications suggest that using NIPT to screen women who are found to be at a higher risk of having a baby with Down's syndrome would enable earlier and safer detection of the condition'.

The study, which is funded by the National Institute for Health Research and developed in collaboration with the UK National Screening Committee, will also look at ways to ensure women understand the test and the implications of the results so that they can choose whether or not to have it, explained Professor Chitty.

Women from maternity units in London and the South East will be recruited to the study, which will be launched in November this year. The test, believed to be around 99 percent accurate for Down's syndrome, will also be used to screen for the rare genetic conditions Edwards' syndrome and Patau's syndrome.