More older women are opting for fetal testing to ensure their babies won't have a congenital disease such as Down syndrome. Right now, the main way these genetic tests are done is by extracting some of the fetus' cells via amniocentesis - when the doctor uses a needle to draw fluid from the sac surrounding the fetus - or chorionic villus sampling - when the doctor takes a sampling of the placenta. However, both procedures have a 1-2% chance of ending in miscarriage.

Geneticists have been looking for less intrusive ways to extract fetal cells, and now, a solution may be on the horizon. In 1998, Dennis Lo and his colleagues found that fetal DNA floats freely in the mother's bloodstream. The main problem is separating the mother's DNA from the fetus'. If the fetus is a boy, they look for a Y chromosome, but if the fetus is a girl, they need other criteria.

Recent research has found two ways to do this:

1. Lo and his colleagues found that fetal DNA can be detected with unmethylated Maspin, a tumor-supressing gene that's active in fetal cells of a placenta but not in the mother.
2. Sinuhe Hahn and coleagues found that the fetus' genetic materials which circulate in the mother's bloodstream are actually much shorter than the mother's. In a study of 32 pregnant women, when the group checked their results against chorinic villus sampling, they identified mutations with almost 100% accuracy.

Both tests simply require a sampling of the mother's blood.

Other geneticists are trying to find ways to extract whole fetal cells, rather than just the fetal DNA. Researcher Ester Guetta and colleagues have identified several types of fetal cells that circulate with placenta cells in the mother's blood stream. While extracting a lot of those cells is difficult to do, she's been able to take blood samples that hold 1-2 fetal cells per 20 ml of blood and multiply that number five fold in the lab over the course of 5-7 days. She's used the methodology to predict the fetus' gender with approx 93% accuracy.

Source: Science News (7/22/06) (subscription)