DNA blood test cuts invasive testing for Down`s syndrome

Paris: 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 published on Tuesday 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 one-percent 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 telltale 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 percent 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). Bureau Report