The test has been certified by an US research team from the University of California, San Francisco, who published their results in the New England Journal of Medicine. Some facilities, like Great Ormond Street Hospital, have already started giving similar tests to their patients.
The new approach relies on a cell-free DNA blood test. The test targets small amounts fetus’ DNA floating in the mother’s blood sample. The testing can normally be done after the woman reaches her 10th week of pregnancy, but not before the 14th week.
Researchers announced on Wednesday the new method gives better results and detects fewer false positives than standard testing. They gathered data from almost pregnant 16,000 women and said the new blood testing method correctly indicated all 38 cases with Down syndrome among the unborn children.
They then compared the results with those from standard testing, and the difference was firmly in favor of the blood testing procedure. Standard screening on the same sample of women only returned 30 cases of Down syndrome. More compelling data supporting blood tests was revealed when researchers counted false positives: 854 results for the standard test, compared to only nine returned by the new cell-free DNA blood test.
It is the second time medical specialists review the innovative method. Previously it was thought blood tests were effective only in high-risk pregnant women. Now, researchers are convinced the procedure is ready to replace testing for all women.
“It is clearly a better test than what we’re currently using,” Dr. Mary Norton, study lead-author, said in a press release. “If one is looking at screening specifically for Down syndrome, there’s no question this test is better for that purpose.”
What the test basically does is follow traces of fetal DNA in mother’s blood. A greater amount of cell-free DNA is suggesting that the fetus has Down syndrome. Despite experts acknowledge the new method to be more accurate, they still advise mothers to take further steps in order to make sure the diagnostic is correct before making any decision regarding their pregnancy.
“This is a major advance, but you’re still going to have to confirm the results,” Dr. Joe Leigh Simpson explained, suggesting that invasive tests like amniocentesis should be performed nonetheless.
The test can only be fooled in some extreme cases, such as undiagnosed cancer or if the fetus had a twin that died in the uterus. Also, obese women probably won’t have enough floating DNA in their blood to make the test effective.
Babies born with Down syndrome have an extra chromosome 21 in their DNA. This leads to significant physical and intellectual difficulties for those born with the syndrome, besides certain related health problems.
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