DNA Blood Test Gives Women A New Option For Prenatal Screening : Shots - Health News A simple blood test can analyze bits of fetal DNA leaked in the mother's bloodstream. It's less risky than invasive alternatives like amniocentesis, but it doesn't tell as much about fetal health.

DNA Blood Test Gives Women A New Option For Prenatal Screening

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Expectant mothers have to make a lot of decisions, like whether they want to know if their fetus has chromosomal disorders like Down syndrome. If parents do want to know, there are several ways to go about testing each with its own pros and cons. Today in Your Health, we're going to look at some new testing technology that women are choosing. But as NPR's Nell Greenfieldboyce reports, it's so new that some women and their doctors don't realize what they have signed up for.

NELL GREENFIELDBOYCE, BYLINE: One woman who opted for this new kind of pregnancy screening is Amy Seitz. She's an epidemiologist, and she's married to a doctor. So she's interested in medical advances.

AMY SEITZ: I think that I initially heard about it through family and friends. Speaking with them, they had - you know, had the option of it given to them by their doctors.

GREENFIELDBOYCE: This kind of test uses a simple blood sample from an expectant mother and analyzes bits of fetal DNA that have leaked into her bloodstream. It's only been on the market since October of 2011. Several companies now offer it.

Seitz got pregnant with her second child last year, and at 35 years old, she knew there was an increased chance of chromosomal disorders like Down syndrome. She didn't want an invasive procedure like amniocentesis or CVS. Those are considered the gold-standard tests but doctors must put a needle into the womb to collect cells that contain fetal DNA, which means a small risk of miscarriage.

SEITZ: I wasn't interested in going as far as getting an amniocentesis because of the risk associated with that. And so when I heard about this test, that was part of the reason that I was most interested in it.

GREENFIELDBOYCE: Seitz says this new way of testing fetal DNA seemed to have already become fairly common where she used to live in Washington, D.C. But she'd recently moved to Alabama, and the clinic she went to there wasn't as familiar with it. Although when she talked to her doctor, she learned they just had a visit from a company sales rep.

SEITZ: You know, I think it was a fairly new test for them at that point. But she was interested in pursuing it further to see what needed to be done.

GREENFIELDBOYCE: Seitz got her blood drawn last July, becoming one of hundreds of thousands of pregnant women who've gone for this new kind of test instead of the more traditional, invasive ones. Doctors say the impact has been huge.

MARY NORTON: Those of us in the field who do diagnostic procedures like CVS and amnio have seen a drastic decrease in the number of those procedures that are being performed.

GREENFIELDBOYCE: Mary Norton is an expert on maternal fetal medicine and genetics at the University of California, San Francisco.

NORTON: Places are reporting doing fewer than half the number of procedures that were being done previously.

GREENFIELDBOYCE: But she says things have changed so quickly that it may be hard for doctors and patients to know what they're dealing with.

NORTON: You know, in three years, yes, they've been around for a little while, but it's still new and it's quite different than previous genetic testing that's been available. It's quite a different paradigm, if you will.

GREENFIELDBOYCE: An invasive test, like an amnio, lets doctors get a complete picture of the chromosomes. And if there's a problem, you know it. You get a solid diagnosis. Until these new tests came along, the only less invasive option was for an expectant mother to get an ultrasound plus have her blood tested for specific proteins. This can reveal if there's an increased risk of certain disorders, but it's not very accurate. It produces a lot of false alarms. Norton says studies have shown that the new fetal DNA tests do a better job. They're less likely to flag a normal pregnancy as high-risk.

NORTON: They're much more accurate than current screening tests, but they are not diagnostic tests in the sense that an amniocentesis is. And so I think that has led to some confusion.

GREENFIELDBOYCE: Even though the newer blood tests do look at fetal DNA, they can't give a definitive answer like an amniocentesis can. That's because they are analyzing scraps of fetal DNA in the mother's blood, and they're all mixed up with her own DNA. Norton says when women get worrisome results from one of these new tests and are referred to her center, they sometimes don't understand why doctors are offering a follow-up amnio.

NORTON: Because they were under the impression that this was as good as an amnio.

GREENFIELDBOYCE: She's concerned that some people might end a pregnancy without getting confirmatory testing. She points to one study last year that found a small number of women did that.

NORTON: You know, there's at least some evidence that it's happening to a greater degree than I think many of us are comfortable with.

GREENFIELDBOYCE: The tests are being used more and more widely. Some worry that the company's websites and marketing materials don't make the limitations clear enough. But Lee Shulman doesn't see it that way. He's an obstetrician and geneticist at Northwestern University in Chicago who's consulted for a couple of the testing firms.

LEE SHULMAN: Patients need to understand that while this is better, it is not a diagnostic test. And I think the companies have done a great job in putting this material out. Whether or not clinicians use this material and take it to heart and use it for patient counseling is a different story.

GREENFIELDBOYCE: He says this technology is so new that a lot of doctors have no experience with it. And consumers need to understand that.

SHULMAN: If the patient - if the couple are not getting the answers, not getting the information they feel comfortable with, they need to seek out prenatal diagnostic centers, maternal-fetal specialists, clinical geneticists who may have more experience.

GREENFIELDBOYCE: For example, here's one thing that might turn out to be a little more complicated than you'd expect. Along with screening for the common chromosomal disorders, companies offer parents the chance to learn their baby's sex weeks before it's clear on a sonogram. Diana Bianchi is an expert on prenatal genetics at Tufts University Medical Center.

DIANA BIANCHI: Many women are very excited by the idea that as part of their blood testing, they could find out pretty definitively if the baby is a boy or a girl.

GREENFIELDBOYCE: She says what they may not realize is that the test will also determine whether there's something abnormal about the sex chromosomes, which isn't that uncommon.

BIANCHI: Approximately 1 in 700 pregnancies, there's an extra X or an extra Y.

GREENFIELDBOYCE: These are mild conditions, but they normally would go undetected unless a woman had invasive test like in an amnio. Amy Seitz in Alabama, thought it was a bonus that getting this new blood test would tell her if she was having a boy or a girl. But it didn't actually do that because of a paperwork glitch.

SEITZ: The box for sex got unchecked somewhere along the way, so we weren't able to find it out from the test.

GREENFIELDBOYCE: The results she did get were reassuring. Nell Greenfieldboyce, NPR News.

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