A more accurate and safer prenatal test for Down's, Edwards' and Patau's syndromes is to be offered by the NHS from 2018, it has been announced.
The UK National Screening Committee had recommended introducing the blood test, known as non-invasive prenatal testing (NIPT), earlier this year, based on the results of an evaluation study (see BioNews 835).
The test analyses fetal DNA circulating in the mother's blood. It carries no risk of miscarriage and has an accuracy rate of 99 percent. Currently, pregnant mothers are offered screening to identify those most at risk of carrying a fetus with a chromosomal abnormality. Those at highest risk are then offered amniocentesis – an invasive test in which a needle is used to take a small sample of amniotic fluid. This carries a risk of miscarriage of around one in 100, resulting in around 46 miscarriages every year in the UK.
The new blood test will only be offered to the approximately 10,000 high-risk women who are currently offered amniocentesis. If the test is positive, women will still be offered amniocentesis as it is the only definitive test, but the Department of Health calculates that there will be only 1400 invasive tests a year and three miscarriages as a result.
Sir David Spiegelhalter, professor for the public understanding of risk at the University of Cambridge, said that the blood test would lead to around 20 more positive diagnoses of Down's syndrome each year.
The news has been met with anger from the campaign group Don't Screen Us Out, which argues that many women will feel pressured into having NIPT and then aborting a fetus with Down's syndrome. However, recent statistical analysis from the University of Cambridge suggests that NIPT is unlikely to increase current abortion rates.
'There's been a lot of concerns expressed about the increased number of terminations,' Professor Spiegelhalter told The Guardian. 'In the assumptions under the current model that's not the case. The estimate is that there wouldn't be a change.'
He points out that the test is being introduced purely on safety grounds. 'People feel very strongly about it, of course they do. It's all the more reason to stand back and look at the figures,' he said. 'There's a mismatch at the moment between the official basis on which this is being rolled out and the discussion around it.'
Professor Alan Cameron, a fetal medicine consultant at Queen Elizabeth Hospital in Glasgow, argued that presenting a more balanced view of Down's syndrome might result in more women choosing to keep the pregnancy: 'The whole essence of a good screening programme is the counselling you have. My experience is that much fewer women would terminate now than they ever did before. People see Down's kids having good, healthy, lives, working in the community, you see kids around with Down's syndrome that are doing a good job.'