New prenatal genetic test gives parents more answers

New applications of a genetic test could help parents learn more about the genetics of their unborn children.

Three studies released Wednesday in the New England Journal of Medicine highlight the use of microarray testing as the latest technology in chromosome analysis. Researchers suggest using this test to identify potential intellectual disabilities, developmental delays, autism and congenital abnormalities as well as determining why a pregnancy failed.

During pregnancy a number of tests are suggested by the American College of Obstetricians and Gynecologists based on the mother's age, medical history or ethnic or family background, along with results of other tests. Chromosomal microarray analysis is a genetic test that finds small amounts of genetic material that traditional testing such as karyotyping cannot detect.

The genetic material is obtained during a regular amniocentesis (where small amounts of amniotic fluid and cells are taken from the sac surrounding the fetus and tested during the second trimester of pregnancy) or another commonly used test called CVS, or chorionic villus sampling (where a small amount of cells is taken from the placenta during the first trimester).

According to one study, this prenatal testing surpassed standard testing to detect more genetic abnormalities. Lead study author Dr. Ronald Wapner, says with microarray, doctors don't look at chromosomes and are able to evaluate smaller pieces of DNA.

If potential development issues are found, "we are way better able to counsel parents about what they would mean for the child," Wapner says. "... We can modify the course and improve the outcome for the child." This type of testing can also be helpful to researchers, as learning what genes cause certain problems may lead to development of potential cures and treatments, he says.

Adequate counseling for parents is needed in case tough decisions need to be made regarding the pregnancy, given the testing outcome, Wapner says.

Dr. Nancy Rose, chair of the American College of Obstetricians and Gynecologists' committee on genetics, says the organization is going to review the studies but can't comment on them yet. However, Rose, who is also the director of reproductive genetics for Intermountain Healthcare, says as a reproductive geneticist, "It's a great promising new technology, but the clinical application really needs some careful evaluation" because of any potential ethical issues.

The second study examined microarray testing in relation to stillborn babies. According to the National Institutes of Health, 1 of every 160 births in the United States is a stillbirth. Parents and doctors often don't know why the babies didn't survive. In this study researchers were able to help parents better understand the reason their baby didn't survive and provide them with information that may one day lead to a successful pregnancy. The microarray testing can be done on tissue that is not alive, where previous tests require live tissue.

"It's a great test for patients who have a pregnancy loss," says Rose, "... and it's superior to detect genetic changes in fetuses that have birth defects."

The third paper was a case report of a specific genetic condition that was not detected prenatally by karyotyping, ultrasounds or the microarray testing, underscoring the limitations to these tests and the potential advantage of the genetic sequencing approach.