A new DNA blood test has been proven to be accurate in the detection of Down syndrome in unborn children.
Down syndrome, also called Trisomy 21, occurs when a baby is born with an extra copy of the chromosome 21.
According to WebMD, the symptoms of Down Syndrome include short stature (height), low muscle tone, a short wide neck, and short stocky arms and legs. Other facial feature symptoms include slanted eyes, a nasal bridge that looks as though it has been pushed in, small ears, an irregular shaped mouth and tongue, and irregular and crooked teeth.
For years, the standard testing for Down syndrome involved undergoing an amniocentesis or CVS (chorionic villus sampling). Amniocentesis involves placing a long, thin needle into the womb to extract the amniotic fluid from the placenta between the 14th and 16th week of pregnancy. The fluid is then sent to a laboratory for analysis. CVS is done by extracting small bits of tissue from the placenta where it attaches to the wall of the uterus. CVS can be done earlier than an amniocentesis, at around 10 weeks, and the results are usually delivered within 10 days of testing. While both of these tests can be relatively accurate, they do deliver many false positives and carry a small risk of the woman encountering a miscarriage.
Now, doctors have discovered a new blood test, called a cell-free DNA test, that can screen fetuses for Down syndrome. So far, the test has proven to be far less invasive and far more accurate.
“With advances in genetics, one can sequence that DNA, and measure the amount that comes from each of the chromosomes,” said Dr. Mary Norton of the University of California, San Francisco, according to VOA News. “And by doing that, you can say, ‘Oh, look there’s extra here that comes from chromosome 21 that’s consistent with the fetus having Down syndrome.'”
According to Fox News, the new study, published in the New England Journal of Medicine, has been the largest study done that shows accurate testing, even in low-risk women. However, the test is not considered diagnostic and it may be necessary for other testing to be done, especially if the woman is considering terminating the pregnancy.
“This is a great test for detecting Down syndrome but it doesn’t detect everything, it isn’t diagnostic, and it doesn’t always work to provide a result,” Norton said.
“There are some false positives and false negatives, so we do still consider it a screening test that needs to be confirmed by a CVS or amniocentesis if the results are abnormal. But it’s far, far more accurate than the last generation screening tests that are currently being done most of the time now.”
The researchers studied 16,000 women pregnant women. They found that the cell-free DNA blood test correctly identified the 38 fetuses that had Down syndrome in the group. However, the standard screening using amniocentesis and CVS only identified 30 of the 38 cases. 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,” said Norton.
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