Maternal Blood Test Might Reveal Fetal Health

Early research points the way to safe, accurate prenatal screen

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By Randy Dotinga
HealthDay Reporter

FRIDAY, Oct. 7, 2005 (HealthDay News) -- New research is moving scientists closer to the holy grail of prenatal medical care: a maternal blood test that could reveal health problems in an unborn child.

Researchers from Hong Kong reported this week that they've discovered a potential new way to differentiate the DNA of the mother from that of the fetus in a maternal blood plasma sample. The key, they say, lies in a DNA trait that's much more common in maternal genetic material.

Specialists couldn't predict how long it may take for the findings to translate into a routine fetal DNA screening test available in the doctor's office. And the study results don't appear to have any bearing, at least for now, on controversial fetal DNA tests that promise to predict a baby's gender early in pregnancy.

Still, the research is promising, said Dr. Siobhan Dolan, associate medical director at the March of Dimes. "This study is a step in the right direction," she noted.

Currently, the best screening tests for fetal medical problems -- including amniocentesis -- are also potentially dangerous to the unborn child. Doctors and researchers have been looking for a noninvasive test, and a test using the mother's blood would certainly fit the bill (current blood tests for pregnant mothers don't directly measure the health status of the fetus).

The good news is that a small bit of fetal blood does blend in with the mother's blood. "The trick is to find a way to sort out in the blood what came from the fetus and what came from the mother," Dolan said.

Only about 3 percent of DNA in maternal blood plasma comes from the fetus, said study author Dennis Lo, a professor of chemical pathology at the Chinese University of Hong Kong. There are ways to differentiate the fetal DNA, such as looking for the male Y chromosome, he said, but that only works for male fetuses.

In the new study, Lo and his colleagues report that they can differentiate maternal from fetal DNA by looking for a specific gene that acts differently in mothers and fetuses. They also used their technique to accurately detect cases of pregnancy-associated hypertension, also known as preeclampsia, in pregnant women.

The findings appear in this week's early online edition of the Proceedings of the National Academy Sciences.

Earlier this year, researchers reported that they were able to more easily analyze fetal DNA by boosting its levels in blood samples. Scientists have also found a way to separate bits of maternal and fetal DNA by analyzing their size.

The new research may have implications for existing fetal DNA tests, such as those that detect potentially dangerous blood group incompatibilities between mother and fetus, Lo said. It's not yet known if the tests will help pick up other diseases like Down syndrome, but researchers are hopeful, Lo said.

More information

To learn more about the types of prenatal tests that are currently available, go to the March of Dimes.

SOURCES: Siobhan Dolan, M.D., M.P.H., associate medical director, March of Dimes, White Plains, N.Y.; Dennis Lo, D.Phil, professor, chemical pathology, Chinese University of Hong Kong; Oct. 3-7, 2005, Proceedings of the National Academy Sciences online

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