Researchers at Drexel University of Medicine in Philadelphia have developed a new diagnostic test that may offer pregnant mothers a new, quicker way to detect Down Syndrome in fetuses.
The new test takes various factors into account, including a combination of two blood tests from the mother, an ultrasound and the mother’s age.
Dr. Ronald Wapner, the lead researcher, claims that the accuracy of the new test is much greater than the current tests popular in the United States today.
Current testing in the United States involves a screening of four different variables, including three measurements from the blood and the maternal age of the woman.
The new test is also an improvement in that it yields results as early as 12 weeks in the first trimester of the pregnancy. The current screening approach misses about 25 percent of Down Syndrome fetuses and does not generate results for about 20 weeks into the woman’s pregnancy, which is the second trimester.
If a woman decides to abort the fetus, 20 weeks into the pregnancy is often too late because abortion is difficult to obtain and may pose a threat to the mother’s health.
“The tests involve taking only a little blood from the mother during the second trimester. Considering the woman’s age, the risk will then be pronounced ‘elevated’ or ‘normal’ based on the test results,” said Dr. Sabine Droste, University of Wisconsin professor of obstetrics and gynecology.
The new test uses a similar screening method to the current one, but the researchers added a new blood test for hormone inhibin A to increase the reliability of the test.
Increasing the reliability will decrease the amount of “false positives” generated, which will decrease the number of women who will have to turn to the invasive diagnostic procedure, Droste said.
While the false positive rate is decreased from the current testing rate, false positives do still exist with the new test. The researchers incorrectly identified a Down Syndrome baby nine percent of the time.
The syndrome is the most common chromosomal birth defect, occurring in one in every 800 babies, and the age of the mother is a very important factor in this testing because the risk of disease increases with the age of the mother.
“The baby inherits three, instead of two, copies of the 21st chromosome, which results in mental retardation and also the possibility [of] birth defects. Affected individuals have a shortened life expectancy, short stature and a need for a protective environment all their lives,” Droste said.
Despite the decrease in number of incorrect screenings, Jackie Tillett, certified nurse-midwife of the UW Medical School department of obstetrics and gynecology, said caution must nonetheless remain a key component during testing.
“I think that these tests should be available to women with careful discussion of the possible results. The false positive rate of nine percent could be devastating to families, ” Tillett said. “Further testing would need to be done before life-changing decisions should be made.”
