A DNA test of a pregnant woman's blood is more accurate than current methods of screening for Down syndrome and other common disorders, new research has found. If other studies bear this out, it could transform prenatal care by giving a more reliable, noninvasive way to detect problems very early in pregnancy.
That would let couples decide sooner whether to have an abortion or to prepare for a major medical problem. It also might cut down on the 200,000 invasive tests like amniocentesis done each year in the United States to diagnose or rule out problems in a fetus.
“It offers women a safe and accurate alternative” for screening, said the study's leader, Dr. Diana Bianchi of Tufts Medical Center in Boston.
Several companies already sell the DNA blood tests, which can be done when the fetus is only 9 to 10 weeks old, a couple of weeks earlier than current methods.
The tests screen for disorders caused by extra or missing chromosomes, such as Down syndrome, which occurs in about one of every 700 pregnancies.
Current screening methods are imprecise. Ultrasounds and various blood tests can hint at a problem but don't directly test for one.
The next step is diagnostic testing — amniocentesis, like a needle biopsy to collect fetal cells, or chorionic villus sampling, which takes a snip of the placenta.
The DNA tests aim to improve screening and lower the number of women referred for the more invasive tests.
The new study, whose results were published Wednesday by the New England Journal of Medicine, is the first to look at the tests' use in a general U.S. population.
Several independent experts called the new research a good first step, but not enough to warrant using the DNA tests now in the general population.
“It's encouraging,” but doctors will want to wait for other and larger studies underway now of various fetal DNA tests, said Dr. Nancy Rose, a University of Utah professor who heads the genetics committee of the College of Obstetricians.
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