A safer prenatal test for Down’s syndrome due to be introduced on the NHS is not predicted to lead to more pregnancies being terminated, according to one of Britain’s most eminent statisticians.
Sir David Spiegelhalter, professor for the public understanding of risk at the University of Cambridge, said that the best evidence available suggests that the blood test, which will be made available in 2018, would lead to an increase of around 20 in the number of positive diagnoses made each year through screening.
He added the test would result in far fewer women opting for invasive testing, reducing miscarriage numbers.
Spiegelhalter cautioned that this evidence sometimes appeared to have fallen out of view in debates in which some campaigners have warned that a generation with Down’s syndrome could be “screened out”.
“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.”
According to the Department of Health’s own projections, Spiegelhalter said, more than 40 miscarriages would be avoided every year because far fewer women would be given amniocentesis, an invasive test in which a tiny amount of fluid is removed from the womb. He added, however, that it was impossible to predict exactly how families would respond to the new screening regime.
“There’s been a lot of concerns expressed about the increased number of terminations,” said Spiegelhalter. “In the assumptions under the current model that’s not the case. The estimate is that there wouldn’t be a change.”
The new test, which works by detecting tiny quantities of foetal DNA circulating in the mother’s blood, will be offered to about 10,000 women a year who are considered to have a higher chance of giving birth to a baby with Down’s syndrome, or two rarer genetic conditions: Edwards’ and Patau’s syndromes.
The test is offered after the standard screening that all pregnant women receive at 12 weeks, which involves an ultrasound and a blood test.
According to recent Department of Health figures, 7,900 women agreed to an invasive test and 46 miscarried. More than 3,000 chose not to have the test for fear of losing their baby or because they would wish to continue with their pregnancy regardless of the result. The figures showed 1,031 Down’s cases detected in a year.
The blood test, which predicts Down’s syndrome with more than 90% accuracy, means most high-risk women will be able to avoid amniocentesis. The government predicts that around 10,000 women would opt to have the non-invasive prenatal test (NIPT). Of these, the Department of Health predicts that most would be screened out and fewer than 1,500 would proceed to the invasive test, where 1,055 Down’s cases would be positively identified.
The motivation for introducing the new blood test is safety, but controversy has been building based on concerns that far more parents would be inclined to find out if their baby was affected by a genetic disorder, potentially leading to more pregnancies being terminated.
In a BBC documentary last month, A World Without Down’s Syndrome?, actor Sally Phillips, whose son Olly has Down’s syndrome, raised concerns about the new test and highlighted the joy that her son had brought to her family.
Spiegelhalter said he “in no way seeks to criticise the campaign groups”, but wants to give people access to the best evidence available. His analysis is due to be published on the website of the Winton Centre for Risk and Evidence Communication at the University of Cambridge, which launched last week and will aim to provide unbiased statistics on public health and policy issues.
Philip Dunne, the health minister, said: “We want women to be able to access the safest screening tests available, so based on the clinical evidence, we have approved the use of a new non-invasive prenatal test for Down’s, Edwards’ and Patau’s syndromes. By offering non-invasive prenatal testing, fewer pregnant women will go on to be offered diagnostic testing which carries a risk of miscarriage.”
Lynn Murray, spokesperson for the campaign group Don’t Screen Us Out, said that the concerns of those opposed to the policy went beyond the projected screening statistics. “We are very disappointed that the Department of Health have approved the NIPT roll-out without consultation with the very group that this is going to have the biggest impact on, people with Down’s syndrome and their families,” she said. “The government has admitted itself that it has made no assessment of the impact this will have on the community of people with Down’s syndrome.”
New prenatal test for Down"s syndrome "will not lead to more terminations"
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