London, June 21 : A simple, risk-free blood test that can detect Down's syndrome from the blood of pregnant women has raised the prospect of screening being routinely available to every expectant mother.
Researchers in Hong Kong have developed a way of identifying genetic markers, which show whether an unborn child has the chromosomal disorder, without relying on risky amniocentesis techniques.
The experimental procedure has been shown to diagnose 90 per cent of Down's syndrome cases in a small trial, while also correctly identifying 97 per cent of foetuses that do not have the condition.
Scientists hope that if the procedure can be refined and its accuracy improved, it could replace more invasive testing techniques within three to five years.
The most common prenatal test for Down's syndrome involves amniocentesis or chorionic villus sampling (CVS) in which a sample of the fluid surrounding the foetus is collected and analysed.
Both procedures are invasive and and carries a one per cent risk of miscarriage. As a result, it is only usually carried out if there is a high enough risk of a disorder - in older mothers, for example.
The Non-Invasive Prenatal Diagnosis (NIPD) test would do away with these risks, but at the same time, would create an ethical dilemma for many couples following a positive result. There are fears that the new approach could ultimately lead to a greater number of abortions.
Nigel Carter, of the Wellcome Trust Sanger Institute, near Cambridge, whose team is working on the technique, said: "As well as your ultra-sound scan, you would have a few millilitres of blood taken for your Down's test."
"It's the sort of procedure that could move from being offered only to mothers at risk, to become a more normal screening procedure," Times Online quoted Carter, as saying.
Down's syndrome occurs when three copies of chromosome 21 are inherited instead of the usual two, causing learning difficulties, often accompanied by serious cardiac defects and a high risk of early-onset dementia.
The NIPD study is published in the journal Nature Medicine.