DNA Blood Test Detects Down Syndrome: It's Less Invasive, But Is It Right For Your Pregnancy?

New findings published in the New England Journal of Medicine discuss a new DNA blood test that has been found accurate in detecting Down syndrome during pregnancy, which occurs when a baby is born with an extra copy of chromosome 21.

For the study, researchers examined about 16,000 pregnant women. They discovered that the cell free DNA test identified all 38 fetuses that were affected by Down syndrome, according to the American Live Wire. For the standard screening methods that typically involve amniocentesis or CVS (chorionic villus sampling), it was much less accurate, detecting only 30 out of the actual 38 affected cases.

Amniocentesis involves placing a long, thin needle in the womb from the placenta between the 14th and 16th week of pregnancy. The fluid that's retrieved is then sent to a laboratory for analysis, where as CVS involves a small extraction via bits of tissue from the placenta that attach to the wall of the uterus. CVS can also be completed a bit earlier than amniocentesis at 10 weeks with results delivered 10 days after completion. Both tests can be relatively accurate. However, they can carry false positives, as well as a small risk of miscarriage.

Of course, the test may not be right for everyone. If women are considering terminating their pregnancy, they may require a more diagnostic approach, including the aforementioned more invasive procedures, to rule out any false positives. And while there were nine false positives in the study, the false positive rate for the new fetal DNA test was only 0.06 percent versus 5.4 percent for standard screening.

"Those women who do opt for cell-free DNA testing should be informed that it is highly accurate for Down syndrome, but it focuses on a small number of chromosomal abnormalities and does not provide the comprehensive assessment available with other approaches," concluded lead study author Dr. Mary Norton of the University of California, San Francisco, via VOA News.