Researchers said Wednesday that using a new fetal DNA tests–Roche blood test–to screen fetuses for Down Syndrome can be much more effective than standard prenatal screenings in low-risk women. Their new study, which was published in the New England Journal of Medicine, is the largest study to demonstrate the accuracy of fetal DNA tests.
Along with the other researchers, Dr. Mary Norton of the University of California, San Francisco, tested about 16,000 women with an average age of 30. The experts compared Roche’s Harmony test to the standard prenatal screening within the group of women. Standard screening consists of a fetal ultrasound and depends on biomarkers in the blood.
The standard screening identified 30 cases of Down Syndrome whereas the Roche test identified all 38 cases in the pregnant women. The standard screening had a false positive rate of 5.4 percent, but the Roche test had a rate of 0.06 percent.
Although the test results can be accurate, experts warned women who test positive to still confirm the results using a more invasive procedure. A more invasive diagnostic test would be amniocentesis.
Norton said that the test is great for detecting Down Syndrome and it is a “major advance.” However, she said that the test “doesn’t detect everything” and it does not always “provide a result.”
For instance, around 500 of the women did not receive any results from the fetal DNA test due to lack of fetal DNA in each woman’s blood. The test focuses specifically on Down Syndrome. Therefore, further tests concluded that nearly 2.7 percent of the fetuses had chromosomal defects that could not have been detected using the fetal DNA test, according to Reuters.
A letter published in the New England Journal of Medicine by Ankita Patel and colleagues of Baylor College of Medicine and the Chinese University of Hong Kong stated that women should not terminate pregnancies based on these sort of screenings. Patel said that women thought the fetal DNA test is diagnostic “because it’s genetic.”
The FDA is looking into regulating the tests. Patel thinks that regulating the tests are a good idea because it would “give women more disclaimers” so that they are aware of “what they are getting into.”
