BY Shirley Butler
March 3, By
Merritt McKinney NEW YORK, Mar 03 (Reuters Health)
Despite
claims that blood tests are more effective at detecting Down syndrome during
pregnancy, study results show that the traditional method of using a mother's
age and routine ultrasound testing is just as effective.
Down
syndrome is a disorder that causes mental retardation as well as physical
abnormalities. Since women 35 and older are most likely to give birth to a baby
with the condition, the traditional way to detect Down syndrome has been to
consider a woman's age in combination with routine scans during pregnancy. But
since 1992, blood tests have been the preferred method for detecting Down
syndrome in the womb, according to a report in the March 4th issue of the
British Medical Journal. But there has been little evidence to back up the
claim that blood, or serum, testing is more effective than using age and
ultrasound results to predict the risk, according to the study's lead author. "If
you asked most obstetricians about the evidence for serum screening, I am sure
that they would tell you that the case for its use was unassailable," Dr.
David T. Howe, of the Princess Anne Hospital in Southampton, England, told
Reuters Health. "In fact, there has never been a controlled study of its
effectiveness anywhere in the world."
According to
Howe, the blood test was adopted widely, despite its higher cost, based on the
assumption that it could detect two-thirds of the cases of Down syndrome, while
screening by maternal age would detect just one-third of cases. These
assumptions are false, according to Howe, since the current study shows that a
woman's age and routine screening can detect about two-thirds of cases of Down
syndrome. In the study, Howe and his colleagues evaluated the effectiveness of
screening by maternal age and ultrasound scanning in all women who gave birth
at Princess Anne Hospital and its branches from 1993 to 1998. During that time,
31,259 babies were born, including 53 infants with Down syndrome. If something
appeared out of the ordinary on the ultrasound, women were given the option of
undergoing amniocentesis, a procedure that involves extracting fluid from the
womb to test for abnormalities. Overall, the traditional screening method
detected 68% of cases of Down syndrome, considerably higher than the often
cited 30%.