Within five years, this test should be available and could ultimately replace the need to perform an amniocentesis:

A prenatal test that analyzes a mother’s blood and father’s saliva may one day be all it takes to check a fetus for genetic illnesses, replacing one that requires drawing fluid from the uterus, a study suggests.

Scientists have sequenced the DNA of a fetus at 18 weeks of pregnancy using the technique. Their analysis found 39 of the baby’s 44 brand-new mutations, not shared with either parent, according to the study published today in Science Translational Medicine.

Scientists compared their method with a traditional gene sequence from the umbilical cord once the baby was born and found the experimental method was 98 percent accurate. The results may point to a new way to scan a fetus’s genome for mutations that can cause illness, such as Huntington’s disease and Down syndrome, without inserting a needle into a pregnant woman’s uterus to draw amniotic fluid, the current practice.

“Part of what this study does is expand thinking about how genomics can be relevant,” said Jay Shendure, one of the study authors and an associate professor of genome sciences at the University of Washington in Seattle, in a telephone interview. “The main advantage is that it’s not invasive.”

The current testing method, called amniocentesis, carries a risk of miscarriage. Even with no additional risk, though, most women probably would want a less-invasive test, Shendure said.

About 10 percent of cell-free DNA in a pregnant woman’s blood comes from her fetus, Shendure said. He and fellow researchers compared groups of the mother’s genes that reside on the same chromosome. Using these groupings, the researchers were able to pick out which genes were new to the baby.