Fetal Leak Leads to Prenatal Test

Scientists say they have for the first time screened blood from a mother for signs of genetic disease in her fetus. The technique may someday offer an alternative to invasive methods of prenatal diagnosis, such as amniocentesis and chorionic villus sampling (CVS), which increase slightly the risk of miscarriage.

Yuet Wai Kan and colleagues at the University of California, San Francisco, extracted fetal cells from maternal blood to check whether fetuses had the genes for two recessive diseases: sickle cell anemia and a similar condition called beta-thalessemia. Their results appear in the November Nature Genetics.

The method relies on the fact that a handful of cells from fetal blood leak into the mother's blood through the placenta. The scientists isolated fetal red blood cells from the blood of two pregnant women, each a carrier of one of the diseases. They stained the cells with an antibody to a fetal protein and plucked them out with a tiny needle. Standard DNA analyses revealed that neither had inherited the two copies of the gene necessary to develop symptoms, and CVS tests confirmed the results. One drawback, Kan says, is that the test won't work on fraternal twins as it cannot discern which fetus the cells came from.

A non-invasive test performed early in pregnancy would be "very attractive" for many women, says Mary Mahowald, a bioethicist at the University of Chicago. But first such a procedure must be vetted in more people. "We've shown that this is feasible," says Kan, "but we need more tests to show how accurate this is."