Simple New Blood Test for Down Syndrome: Does It Give You Peace of Mind?

pregnant woman getting blood drawn

When you're pregnant, of course you want as much (accurate) info as you can get about the baby growing inside you, so listen up: A DNA blood test usually only given to pregnant women at high risk of having a baby with Down syndrome is way more accurate than the standard screening test -- and can benefit all women. 

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It's called cell-free fetal DNA testing, and it examines the tiny bits of your fetus's DNA floating around in your blood. (Sounds kind of gross, but when you're tested, blood is taken from your arm and sent to the lab, per usual.)  It's done early on -- after just 10 weeks of pregnancy.

Right now, this DNA testing, which has been on the market since 2011, is usually offered to women over 35 or at high risk of having a baby with Down syndrome. Most other moms-to-be get screened via a blood test that looks for abnormal hormone and protein levels associated with chromosomal defects. There's also an ultrasound screening that measures fluid under the skin at the back of the fetus's neck, another marker of Down syndrome.

But cell-free fetal DNA testing has been gaining in popularity in recent years, and more and more doctors are using it. (Although whether your insurance will cover it is a whole different story.)

Let's be clear, though. Cell-free fetal DNA testing can detect abnormalities, but it can't provide a definitive diagnosis. Any results must be confirmed through a more fine-tuned test like amniocentesis.

But as a screening tool, cell-free fetal DNA testing (please, someone give this a cute nickname and quick!) is better than the standard first-trimester tests moms-to-be currently undergo. So says new research hot off the press in the New England Journal of Medicine (and hey, we trust 'em).

Here's what you need to know about it:

The good:

The test is more accurate. This study, headed by researchers at University of California, San Francisco was huge -- like 16,000 women huge. The test correctly ID'd 38 fetuses with Down syndrome. (Standard blood tests only found 30.)

It's also better at ID'ing other chromosomal defects. The test correctly flagged 9 out of 10 fetuses with another chromosomal defect called Edward's Syndrome and 2 out of 2 fetuses with trisomy 13 or Patau Syndrome.

More from The Stir: Mom Shares Beautiful Journey of Raising a Child with Down's Syndrome

The bad:

It's not flawless. The test relies on there being enough fetal DNA floating in your blood. In the case of 500 of the pregnant women who participated in the study, there wasn't enough. But when further testing was done, 2.7 percent of fetuses did have chromosomal defects.

Like we mentioned, it's not a replacement for amnio. (Sorry!) This test analyzes your baby's DNA which is mixed up with your own, so it can't give you an actual diagnosis like amniocentesis, which relies on a sample of amniotic fluid. You want definitive answers, you still gotta go the needle-in-the-stomach route. 

Will you ask your doctor about this new test?

 

Image © iStock.com/lostinbids

 

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