The research team led by Kypros Nicolaides at Kings College London has released results from a study of 1000 women receiving non-invasive fetal DNA testing for Down’s syndrome.
Currently, 3-5% of pregnant women in the UK undergo invasive testing for the diagnosis of genetic abnormalities, because there is a high risk the foetus is affected. As there are now well over 700,000 pregnancies each year in the UK, this equates to at least 21-35,000 invasive tests, of which around 1% will result in miscarriage. New non-invasive tests using fetal DNA present in the mother’s blood from early in pregnancy are therefore a great advance for antenatal care.
The new data reports on women with a median age of 37 who were given fetal DNA testing at ten weeks for trisomies 21 (Down’s syndrome), 18 (Edward’s syndrome) and 13 (Patau syndrome). This was followed by standard screening tests at 12 weeks. Positive results were followed by normal invasive diagnostic testing.
Both approaches correctly identified all pregnancies affected by a trisomy, but the false-positive rate (indicating the presence of a trisomy when in fact none was present) differed: 0.01% for the fetal DNA test compared with 3.4% for the normal screening tests. The new test was therefore significantly more sensitive, and dubbed ‘nearly diagnostic’ by Prof Nicolaides, who said the test would offer women clearer information to help make decisions about whether to have invasive testing. He added: "It has been trendy to say we must involve patients in the decision-making process, but it has often been something we only pay lip-service to”.
Experts agree that fetal DNA testing identifies women with high-risk pregnancies much more accurately, but as it is not 100% diagnostic it will probably not replace invasive testing for reliable diagnosis. Instead, it could be used in all those at high risk to refine the screening process and greatly reduce the number of women who need to undergo invasive testing.
The research team at KCL are about to begin a two-year prospective study of 20,000 NHS antenatal patients for a more rigorous assessment of the test.