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A new blood test is offering a safe and more accurate way to perform prenatal screenings for Down syndrome. This is detailed in a new study published today in The New England Journal of Medicine. The findings are being welcomed as an important advance, but there are also some concerns, as NPR's Rob Stein reports.

ROB STEIN, BYLINE: Doctors recommend all pregnant women get screened for Down syndrome. But the tests aren't totally accurate, so some women get false alarms. And Diana Bianchi of Tufts University says that's more than just nerve-wracking. The follow-up tests women get can cause miscarriages.

DIANA BIANCHI: That's what we're really concerned with, at the end of the day, that there's an unintended miscarriage resulting from a procedure that didn't need to be performed in the first place.

STEIN: But there's a new screening test that some doctors have started using. It's easy. All it takes is a blood sample. Then high-speed genetic scanners analyze tiny bits of DNA from the baby that float around in a woman's blood when she's pregnant.

BIANCHI: The blood test is counting sections of DNA, and if there is more DNA than would be expected, it suggests that the baby has an abnormality.

STEIN: But there's been a lot of questions about how often the new test gets it right. So Bianchi and her colleagues tried it on nearly 2,000 women, and it worked better than the standard tests - way better. It's 10 times more predictive, according to the new study.

BIANCHI: It means that a significant proportion of women are not being made anxious, by being told they have an abnormal test result.

STEIN: And that means fewer women will get those follow-up tests that could end up causing a miscarriage.

BIANCHI: It's very good news for pregnant women.

STEIN: Other experts agree the new test is a big deal, but they have some reservations. It'll probably be more expensive. And Michael Greene at Massachusetts General Hospital fears some women may not realize that it's still not perfect.

MICHAEL GREENE: I'm worried that without a proper sense of perspective on the test, women may use a positive screening test as the basis for terminating what would actually have been a normal pregnancy.

STEIN: So it's really important that women still get those risky follow-up tests to be 100 percent sure.

Others have more concerns. Abortion opponents think the test will prompt more women to terminate their pregnancies. And advocates for people with Down syndrome have their own fears. Brian Skotko, a Harvard medical geneticist, says there are still lots of misconceptions about Down syndrome.

BRIAN SKOTKO: People with Down syndrome are artists. They're poets. They're athletes. Their lives are happy ones and fulfilling ones. I have a sister with Down syndrome who certainly is a life coach, for not only myself, but for my entire family. If the new tests become a routine offering, then we have to start to ask: Will babies with Down syndrome slowly start to disappear?

STEIN: And that's not all. The technology the new test uses can scan the entire genetic code of a fetus. So Hank Greely, a bioethicist at Stanford, says it could be used to screen fetuses for all sorts of things.

HANK GREELY: In the near future, you could imagine people testing for your risk of getting Alzheimer's when you're 70 years old, or diseases that don't strike till middle of life, like breast or ovarian cancer, or something as minor as color blindness. I think regulators, legislators, doctors will have to make some hard decisions about what kind of information they want to give parents that parents could then use to terminate a pregnancy.

STEIN: Bianchi says all she's trying to do is to find a better way to screen pregnant women for Down syndrome and similar conditions. Some women may decide they want to end their pregnancies. But for others, it just gives them more time to plan for caring for their new babies, not matter how they come out.

Rob Stein, NPR News.

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