What is cfDNA screening, and why is it being proposed?
The UK has a series of screening programmes that attempt to detect medical conditions in various parts of the general population. One of these programmes is the Fetal Anomaly Screening Programme (FASP).
Through the FASP, pregnant women are offered a ‘combined test’ between 10 and 14 weeks of pregnancy to determine the chance that their unborn baby has Down’s, Edwards’s or Patau’s syndrome. This initial tests are not ‘diagnostic’ – that is, they do not give certainty as to whether a baby has a fetal abnormality – if the ‘combined test’ indicates a high chance of the unborn child having one of these disabilities, a further invasive diagnostic test is offered. These involve a fine needle being used to derive and test amniotic fluid (amniocentesis) or a piece of the placenta (chorionic villus sampling). Such tests carry the risk of miscarriage.
The national body that regulates these programmes, the UK National Screening Committee (UKNSC), is recommending that a new non-invasive prenatal screening technique (or ‘NIPT’) called ‘cell-free DNA’ (cfDNA) testing be introduced into the FASP. This technique works by analysing fetal cells in the mother’s blood, and genetically analysing them for signs of fetal anomalies. The UKNSC has recommended that cfDNA testing is introduced as a second line screening measure following the current combined test.
The UKNSC also commissioned a pilot study by RAPID (Reliable Accurate Prenatal non-Invasive Diagnosis) – a five-year UK national programme funded by the National Institute for Health Research (NIHR) – which concluded that if implemented into the FASP, cfDNA would lead to 102 more babies with Down’s being detected every year. The same study also predicted 25 fewer miscarriages every year due to invasive tests, as a consequence of fewer women opting for such procedures due to the greater confidence they received through a positive cfDNA result.