Preliminary data reported in the February 16th issue of the Journal of the American Medical Association and recently highlighted by March of Dimes Medical Director Nancy Green on CBS’ The Early Show indicate that in the future, laboratory tests may become available that can help doctors determine whether a fetus is at risk for a genetic defect by using as sample of blood from the mother.

Pregnant women commonly have procedures called amniocentesis and chorionic villus sampling (CVS) to determine if their unborn children have genetic birth defects or certain other conditions. With amniocentesis, a needle is inserted into a pregnant woman’s abdomen through to the amniotic sac surrounding the fetus in order to obtain a sample of amniotic fluid for testing; with CVS, either a needle inserted through the woman’s abdomen or a tube inserted through the woman’s vagina and cervix is used to obtain a tissue sample from the placenta. Unfortunately, while amniocentesis and CVS are considered to be generally safe, a small percentage of women miscarry as a result of having the procedures.

Researchers are now trying to find less invasive, safer tests that can provide the same type of information as these more invasive procedures. Recently, Swiss scientists took a major step toward this achieving this goal with a test that uses a sample of maternal blood. It has been known for some time that fetal DNA can be found in the maternal bloodstream during pregnancy. Since maternal DNA sequences can be distinguished from fetal DNA sequences in a mother’s blood sample using a new technique called “size fractionation,” the investigators in this study were able to compare the blood test to CVS for 32 women who were ten to twelve weeks pregnant and were at risk for having a baby with beta-thalassemia (because both mother and father were carriers of a defective gene).

The study reports that the researchers were able to correctly determine the presence of one of four gene mutations that cause beta-thalassemia in the fetal DNA in all but three cases, with only one false-positive test. The investigators believe that this approach may lead to an inexpensive, non-invasive, and accurate test for beta-thalassemia as well as other genetic disorders. It is important to remember, however, that the findings are preliminary – more studies are needed before such a test can be approved for routine use.

Sources
Detection of Paternally Inherited Fetal Point Mutations for Beta -Thalassemia Using Size-Fractionated Cell-Free DNA in Maternal Plasma. JAMA. February 16, 2005;293:843-849. Abstract available online: http://jama.ama-assn.org/cgi/content/abstract/293/7/843

National Library of Medicine Information Page on Beta Thalassemia. Available online: http://ghr.nlm.nih.gov/condition=betathalassemia

March of Dimes Medical Director Appears on CBS Early Show to Discussion New Research on Prenatal Screening. March of Dimes press release, February 16, 2005. Available online: http://www.marchofdimes.com/aboutus/14458_15093.asp

New Era Near For Fetal Screening? Feb. 16, 2005, posted on CBS’ The Early Show Web site. Available online: http://www.cbsnews.com/stories/2005/02/16/earlyshow/health/main674396.shtml

Familydoctor.org. Prenatal Diagnosis: Amniocentesis and CVS. Available online: http://familydoctor.org/144.xml