Within a few years, a pregnant woman might be able to have a simple blood test to determine whether the child she is carrying is afflicted with a number of serious genetic disorders — including Down syndrome, cystic fibrosis and Tay-Sachs disease.

Three studies published or presented this month demonstrate how foetal DNA can be isolated from the mother’s blood and checked for genetic abnormalities.

A test based on such technology could eventually replace amniocentesis and chorionic villus sampling — invasive tests that examine foetal DNA but carry a small risk of miscarriage. Such a test could also ignite new research into how some disorders might be treated in utero, says Dr Kenneth Moise, a professor of obstetrics and gynecology at Baylor College of Medicine in Houston.”This is a new age of being able to diagnose foetal genetic problems by doing a blood test of the mother,” he says. “The beauty of this whole thing is that we can do it at 8 to 10 weeks of pregnancy.”

Researchers have long known that foetal cells circulate in the mother’s blood and scientists have tried vigorously to develop a prenatal genetic test by isolating those cells. The foetal cells, however, are so scarce, Moise says, that “it was like looking for a needle in a haystack.” Moreover, because such cells can remain in a mother’s blood for many years, doctors couldn’t be sure if the cells were from the foetus or an earlier pregnancy.

About 10 years ago, however, new studies revealed that foetal DNA — packets of genetic code from a developing foetus but not whole foetal cells — also could be found in a pregnant woman’s blood. The discovery of this material, called free foetal DNA, launched new efforts to isolate the genetic material.

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