New Blood Test May Signal End of Invasive Prenatal Testing

The newly approved test is more than 99 percent effective at detecting trisomies.

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Every year, more than 200,000 pregnant women undergo an amniocentesis—an invasive procedure in which a needle is inserted into the uterus in order to test for Down syndrome, and other chromosomal disorders. But a new blood test is about to be launched that could drastically cut down on that number.

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Most amniocenteses are performed on older mothers, because their children are at higher risk for "trisomies"—often fatal diseases that are caused by having an extra chromosome. But miscarriages occur in about 1 in 200 amniocentesis cases, and the needle can sometimes come into contact with the fetus. The new blood test, developed by Natera, a California-based genetic testing company, will be available starting March 1, and is more than 99 percent effective at detecting trisomies.

The test may be an option for older women who don't have a history of genetic illnesses in their families. Many amniocenteses are ordered after a hormonal test suggests a fetus may be at risk for a trisomy. But those hormonal tests are often unreliable, leading to unnecessary procedures.

"If a mother wants to know about the genetic health of their fetus, they can either have an unreliable hormone screening test, or a very reliable but risky, and incredibly uncomfortable procedure like an amniocenteses," says Jonathan Sheena, chief technology officer of Natera. "We consider that a false choice—a choice a woman should not have to make in the 21st century."

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Sheena says the test checks 20,000 places in "cell free DNA" that floats in the mother's blood to determine whether or not there are any abnormalities. While the test is useful for detecting trisomies, amniocenteses are still necessary to detect genetic disorders such as cystic fibrosis or Tay Sachs.

"Amnio gets a very big sample of the fetal genome," Sheena says. "What we're getting are lots and lots of small fragments mixed with maternal DNA."

Sheena says they are working on an updated version of the blood test that can also check for genetic diseases and disorders. He expects the more advanced procedure to be available within a few years.

"Amnio has a little more resolution than we can get today, so we're trying to dial up our resolution to be able to test for genetic disorders," he says.

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