Jacob Kitzman and Matthew Snyder, working in the laboratory of Dr. Jay Shendure, an associate professor of genome sciences at the University of Washington, said fetal DNA appears in the mother's plasma a few weeks after conception, rises during gestation and vanishes after the baby is born.
The concentration varies among individuals, but about 10 percent of the cell-free DNA in a pregnant woman's blood plasma comes from the fetus, Kitzman said.
There are other maternal blood tests for major aberrations in the fetus' genetic makeup, but they search for just a few genetic disorders or specific congenital abnormalities.
Kitzman said his team's method could assess many and more subtle variations in the fetus' genome, down to a minute, one-letter change in the DNA code.
"The improved resolution is like going from being able to see that two books are stuck together to being able to notice one word misspelled on a page," Kitzman said in a statement.
Technical advances and statistical modeling made analyzing genetic variations residing on the same chromosome and from these groupings possible. The researchers pick out the parts of the baby's genetic material inherited from each parent with more than 98 percent accuracy, the study said.
The findings were published in Science Translational Medicine.