The new method is the work of scientists at Stanford University and Lucile Packard Children's Hospital in California, and the Howard Hughes Medical Institute in Chevy Chase, Maryland, and was published online on 6 October in the Proceedings of the National Academy of Sciences. The new test does not carry a risk of miscarriage.
Amniocentesis and chorionic villus sampling, the current prenatal gene testing methods, require the insertion of a needle into the uterus and increase the risk of miscarriage by about half a per cent.
The new method scans for occurrences of fetal aneuploidy, an abnormality in the number of fetal chromosomes in the pregnant woman's blood.
For the study, researchers used blood samples from 12 women already known to have aneuploid pregnancies and 6 with normal pregnancies. They then separated the blood into plasma and cells and discarded the cells. This meant they could focus on scraps of DNA floating around in the plasma without being distracted by the DNA of the cells.
The team found that the DNA scraps floating around in the plasma, which came from both the pregnant woman and the fetus, were about 25 to 30 base pairs long, which is long enough to match each scrap to a specific chromosome. By tallying up how many gene scraps came from each chromosome they found that women with Down Syndrome pregnancies had more scraps of chromosome 21 DNA floating in their plasma tha the women with normal pregnancies.
