Aug. 9, 2011 -- Using fetal DNA from a mother's blood to determine the unborn baby's sex is highly effective, according to a new review of the research.

"After seven weeks of gestation, the accuracy of fetal sex detection is very good using maternal blood," says researcher Diana W. Bianchi, MD, a reproductive geneticist and executive director of the Mother-Infant Research Institute at Tufts Medical Center in Boston.

At seven weeks, she found 95% accuracy. "After 20 weeks, it was nearly perfect."

The research involves tests done by hospital or research groups worldwide. "It shouldn't be confused with what the direct-to-consumer companies are advertising [to help parents find out the gender of their unborn infants]," she says.

The hope, Bianchi says, is to use these research-based tests to detect unborn babies at risk for sex-linked disorders, such as hemophilia, and other genetic disorders early in the pregnancy. Depending on those results, it could delay or rule out the need for more invasive tests such as amniocentesis.

The review is published in the Journal of the American Medical Association.