DNA in a pregnant woman's blood can reliably show whether her foetus has Down's syndrome, thus hugely reducing the need for invasive test procedures such as amniocentesis, research said.
Down's syndrome, a major developmental disorder also called trisomy 21, occurs in around one in every 800 live births.
Pre-natal diagnosis mainly entails sampling fluid, drawn by a needle, from the amniotic sac enveloping the foetus. Another technique is called chorionic villus sampling, and entails taking a sample of placenta.
Both techniques, though, carry a roughly 1% risk of miscarriage, which is why they are reserved for older mothers-to-be and other women deemed at risk.
Researchers led by Dennis Lo, a professor at the Chinese University of Hong Kong, carried out the first large-scale investigation into new DNA technology which sequences tell-tale foetal molecules in maternal blood.
The test was carried out among 753 women who were all in the high-risk category.
Eighty-six of them were found to be carrying a foetus with Down's. The test detected this with 96.6% accuracy and did not deliver any "false negatives," meaning that it wrongly said a woman did not have a Down's foetus.
"The sequencing test could be used to rule out trisomy 21 among high-risk pregnancies before proceeding to invasive diagnostic testing," says the study, published online by the British Medical Journal (BMJ).
(Sapa, January 2011)