Paradigm shift in Down’s syndrome screening offers pregnant women safer option
Fertility and Pregnancy Advances mean that thousands fewer UK women will need to undergo invasive diagnostic testing.
Recent technological advances in DNA testing have led to a dramatically improved and much safer prenatal screening test. It requires only a blood sample from a pregnant woman to be able to estimate the chance that her baby may be affected by Down’s syndrome and other serious genetic conditions. The unprecedented accuracy of this new form of non-invasive prenatal testing (NIPT) means that thousands fewer UK women will need to undergo invasive diagnostic testing to determine if their baby has Down’s syndrome.
Currently, screening for Down’s is offered to all pregnant women in the NHS through either the combined test (ultrasound and blood test) or quadruple test (just blood tests only) depending on the stage of pregnancy. These tests identify women at risk of having a baby with Down’s – a result of a 1 in 150 chance is seen as a higher risk (or a ‘positive’ result). All higher risk women have the option of having an invasive diagnostic test (amniocentesis or CVS) to confirm. However at best, the combined and quadruple tests are 75-90% sensitive meaning that up to 25% of all Down’s babies can be missed and additionally, due to the lack of accuracy, not all women who receive a high risk result will actually have an affected pregnancy.
As Dr Brenda Kelly, Consultant Obstetrician and Fetal Medicine Specialist at the John Radcliffe Hospital, Oxford explains, “faced with a higher risk result, the decision whether or not to undergo invasive testing can be agonising for expectant parents. In around 8 of 9 cases the result from the diagnostic test will be normal. However, the price for that reassurance, is the small risk of miscarriage and the associated stress, discomfort and anxiety of the invasive procedure.”
Like most healthcare providers, Dr Brenda Kelly welcomes the move to offer NIPT testing to NHS patients. “This development represents a paradigm shift in prenatal care. With NIPT we now have a test that is over 99% accurate in the detection of pregnancies affected with Down’s syndrome and a very, very low false positive rate. In other words, the true pick-up rate of Down’s is excellent and far fewer women will undergo unnecessary invasive testing. However, it is important to remember that NIPT is a screening, not a diagnostic test; it is accurate, but not 100% accurate so any women with a higher risk result following this new test will still be offered invasive testing.”
In January of this year, the UK National Screening Committee, which advises ministers and the NHS about all aspects of screening, published a report which, whilst recognising the benefits of NIPT, stopped short of full roll–out to all pregnant women on the NHS. Current plans are to offer it only to women deemed at higher risk through the combined or quadruple test. While the details of this implementation are still being developed, several NHS trusts, have already started to offer the tests either free for high risk women, or privately. Pregnant women who want to know more should therefore ask their doctor or midwife for details.