Because a pregnant woman's blood carries pieces of fetal DNA, researchers can devise tests to tell with a high degree of certainty whether the fetus carries extra chromosomes (as an extra chromosome 21 in Down syndrome, for example). They can also test for versions of genes that cause or raise the risk for a disease, potentially screening for a whole slew of genetic disorders in one fell swoop.
And as geneticists learn more about the genetics behind traits such as eye color or hair color, these noninvasive fetal tests will be to pick up on those characteristics as well.
“Prenatal genetic diagnostic technology is advancing at an astonishingly rapid pace,” Bianchi writes. She cites 117 research reports in her paper -- and notes that 53 of them were published in the last two years alone.
The developments hold a lot of promise for personalized fetal medicine, she says, but “time is of the essence” for scientists, bioethicists, physicians, parents and government officials to do some serious thinking and decision-making about how the new advances should be applied and regulated.
Already, noninvasive tests for Down syndrome are on the market in the U.S and several thousand of such tests have been performed. The companies marketing them are tussling with each other over patent rights: One of them, San Diego's Sequenom, Inc., was just denied a request to a California court to block sales of another test, by rival Ariosa Diagnostics of San Jose.
The new tests could soon replace the two-pronged approach currently used, in which a blood test is done first, measuring for abnormal levels of certain proteins. If the protein levels are abnormal, that’s followed by either amniocentesis or chorionic villus sampling, to obtain fetal cells and count the chromosomes.
One might think there could be no down side to move toward a single blood test, since amniocentesis and chorionic villus sampling are invasive and carry a small but finite risk of miscarriage. But even here, Bianchi writes, the experience of future parents and the decisions they ultimately make can be affected. The multi-step process allows future parents several time points at which they can reflect on what they would do if the test reveals their fetus has Down’s. That is not the case if you just have one test and then need to make a decision.
The issues become even messier when one moves beyond that simple example. Figuring out the sex of a fetus is important if the mother is a carrier for a disease that will affect only males. But that has also made gender selection possible.
Whole-genome tests will reveal traits that only raise the risk of a condition, not carve it in stone – which “raises parental anxiety, as well as the possibility of termination of a clinically unaffected fetus,” Bianchi writes.