DNA Blood Test Cuts Invasive Prenatal Testing for Down Syndrome

DNA in a pregnant woman's blood can show whether her fetus has Down syndrome, thus hugely reducing the need for invasive test procedures such as amniocentesis, according to new research.

Down syndrome, a major developmental disorder also called Trisomy 21, occurs in around one in every 800 live births.

Prenatal diagnosis mainly entails sampling fluid, drawn by a needle, from the amniotic sac enveloping the fetus. 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 fetal 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 fetus with Down syndrome. The test detected this with 96.6 percent accuracy and did not deliver any "false negatives."

"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).