Three versions of this test, which can be performed as early as 10 weeks into a pregnancy, have come onto the market since December.
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.)
More is not better
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.