New DNA test could revolutionize prenatal screening

NEW YORK -- A report in the New England Journal of Medicine Wednesday could revolutionize prenatal screening for Down Syndrome and other disorders.

When 29-year-old Jennifer Fontaine was pregnant last year, a standard blood screen suggested her baby had a severe genetic defect.

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Jennifer Fontaine
CBS News
"It was very devastating to read that the baby might not make it through the birth, the baby might be stillborn, or if she does make it through the birth, she might not live up to her first birthday," said Fontaine.

But that standard blood screen isn't definitive and has a high rate of false positive results.

So Fontaine was given the option of either an amniocentesis -- an invasive test that carries a 1 in 600 chance of miscarriage -- or a more targeted blood test which analyzes fetal DNA circulating in the mother's blood. She opted for the blood test.

After waiting for more than two weeks, she got good news; there was no defect.

"It was the best feeling ever to know everything was fine and that in a few months we were going to have a perfect baby little girl, so we were happy," said Fontaine.

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Dr. Diana Bianchi
CBS News
Since 2011, the fetal DNA blood test given to Fontaine has been used to screen high-risk pregnant women for several chromosomal defects. Researchers wanted to find out if this DNA test could be useful for low risk women, as well. They looked at samples from over 1,900 women and found that for Down Syndrome, the standard screening had a 3.6 percent false positive rate compared to 0.3 percent for the fetal DNA screen.

That's a tenfold reduction in false positives.

Dr. Diana Bianchi of Tufts Medical Center led the study.

"Far fewer women are made anxious and need to go on to the further counseling and certainly there's a reduction in the need for an invasive diagnostic procedure," said Bianchi.

The DNA test costs as much as $1,500, but given the potential benefits of avoiding further invasive testing, that might change.


  • Jonathan LaPook

    Dr. Jonathan LaPook is the medical correspondent for the CBS Evening News. Follow him on Twitter at @DrLaPook

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