Friday, February 28th, 2014
A simple blood test taken early in pregnancy is showing high degrees of accuracy in predicting chromosomal abnormalities in fetuses, a study published in the New England Journal of Medicine has found. The finding is welcome news to pregnant women who worry about having invasive prenatal screenings, some of which, like amniocentesis, carry a small risk of miscarriage. More from The New York Times:
The study, published on Wednesday in The New England Journal of Medicine, found that the fetal DNA test was 10 times better in predicting cases of Down syndrome than the standard blood test and ultrasound screening, and five times better in predicting the other disorder, Trisomy 18. It also greatly reduced the number of false-positive results.
It could prevent many women who would otherwise get the standard blood test from needing to confirm positive results with invasive tests like amniocentesis or chorionic villus sampling, which can be stressful, much more costly and carry small risks of miscarriage. “Nine out of 10 women who are currently being referred for further testing would not need invasive tests,” said the lead author of the study, Dr. Diana Bianchi, the executive director of the Mother Infant Research Institute at Tufts Medical Center’s Floating Hospital for Children.
A positive result on the DNA screening would still need to be confirmed with invasive tests, because in more than half the cases in which the newer test predicted a disorder, there was no chromosomal abnormality. But a negative result would provide confidence that these two major chromosomal disorders are absent.
“It’s a better mousetrap, there’s no doubt about that,” said Dr. Michael Greene, director of obstetrics at Massachusetts General Hospital and co-author of an editorial about the study. “If the test is normal, the overwhelming probability is that your fetus is normal. There will be far fewer women who will be encouraged to have invasive testing, and, as a result, far fewer miscarriages.”
The screen analyzes blood from women who are at least 10 weeks pregnant. At that point, about 10 percent of DNA in the blood will be fetal DNA from the placenta, Dr. Bianchi said.
Image: Pregnant woman at the doctor, via Shutterstock
The results of our Ancient Chinese Gender Predictor could spill the beans about whether you’re having a boy or girl.
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Thursday, November 29th, 2012
A relatively new type of blood test that can detect genetic diseases including Down syndrome in pregnant women is making news because it is so much less invasive than amniocentesis, a procedure that carries a small risk of miscarriage, and can be conducted at 10 weeks gestational age. But the new test–three are currently on the market–is expensive, costing nearly $2,000, and is not yet regulated by the Food and Drug Administration. More from The Washington Post:
“Tens of thousands of women have used them, according to the companies that sell the tests. But they are not subject to regulation by the Food and Drug Administration, and questions have been raised about a technology whose accuracy and role are still being assessed. As a result, no major insurance company has yet agreed to cover the tests, whose list prices range up to $1,900.
New medical technologies often challenge a health-care industry grappling with pressures to control costs. It’s not yet clear whether the new tests will cut costs and miscarriages by reducing invasive prenatal diagnostic procedures such as amniocentesis or inflate costs because they’re used by women who probably would never have opted for amnio because of miscarriage fears. (The established tests are performed about 200,000 times annually in the United States and cost roughly $2,500 in the Washington area.)
With the new tests, fragments of fetal DNA extracted from the mother’s blood sample are checked for increased amounts of material from chromosomes 21, 18 and 13, a sign that the fetus carries three instead of the normal two copies of those chromosomes.
In this case, more is not better. Having an extra copy of 21, a condition called trisomy 21, is the main cause of Down syndrome, while having a third copy of 18, a condition called trisomy 18, causes a less common disorder named Edwards syndrome. Trisomy 13 is also known as Patau syndrome. All three conditions are linked to serious developmental and medical problems.
Standard first-trimester screening for these genetic conditions can be performed as early as 11 weeks’ gestation. It consists of a blood test to check levels of pregnancy-associated proteins and hormones in the mother’s blood and an ultrasound to look for extra fluid under the skin at the back of the fetus’s neck. The results are usually available within a week.
Used together, the standard blood tests and ultrasound can detect about 90 percent of Down syndrome cases and an even greater proportion of trisomies 18 and 13. But there’s a false-positive rate of about 5 percent, and only amniocentesis or the much less commonly used chorionic villus sampling, another invasive test that can cause miscarriage, can provide a definitive answer.”
Image: Pregnant woman talking to doctor, via Shutterstock
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