Stephen R. Quake of the Howard Hughes Medical Institute and colleagues at Stanford University said researchers have long known that a pregnant woman's blood contains small amounts of DNA from the fetus.

The researchers devised a way to scan fetal DNA present in the mother's blood to determine whether the fetus' cells contain extra chromosomes associated with several types of severe birth detects.

The test developed is more accurate than techniques used in previous efforts to diagnose aneuploidy by analyzing fetal DNA. Aneuploidy occurs when there are either too many or too few chromosomes in cells.

Down syndrome, for example, is caused by a trisomy -- three copies instead of two -- of chromosome 21.

"We believe this is the first demonstration of a universal, non-invasive test for Down and other aneuploidies," Quake said in a statement. "We need a larger clinical study to understand a bit more about the best way to implement it."

The findings are published in the Proceedings of the National Academy of Sciences.