A new test to identify Down Syndrome
Marc Siegel, MD
Let me tell you about an amazing new test, Materni T21, for identifying the most common chromosomal abnormality in the human fetus, Trisomy 21, or Down Syndrome. This test, now being produced by two companies, Sequenom and Aria, has been found to be sensitive for discovering Down Syndrome in over 99% of cases. The news media has paid too little attention to this important technology.
Since Down Syndrome is present in 1 out of 800 babies—a chance that rises to 1 out of 100 by age 40—and since 50% of Down's babies have significant heart disease, it makes sense to have a good test available to determine whether a fetus has it or not.
Previously, women over 36 years of age or otherwise at high risk of Downs were compelled to have an amniocentesis where a bore needle was placed into their belly at 16 weeks to sample the amniotic fluid. Now, with the widespread availability of the new blood test, it is reasonable for a woman to consider an ultrasound and the Materni T21 test.
For most pregnant women over 40, an agonizing mathematical moment usually takes place at 16 weeks, where the risk of miscarriage from the invasive procedure (about 1 in 200), is compared with the risk of an undetected Downs baby. Now, it appears that this deliberation can be replaced by a blood test.
Any time a risky, invasive test can be replaced by a blood sample, doctors and their patients rejoice. What remains is for this test to prove its utility on a large number of mothers throughout the world. But the new test is off to a very good start.Marc Siegel, MD, is an internist and professor of medicine at New York University and the author of False Alarm: The Truth About the Epidemic of Fear