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% figure, according to the
report.
"Our findings suggest that the advantages of serum screening are much less
in current practice than were suggested in demonstration projects," the authors
write.
The researchers do note, however, that blood testing may be more effective
in younger women, although this needs to be proven.
Although Howe and his colleagues conclude that it may be too late to stop
the move towards blood testing for Down syndrome, they urge that any new
screening methods should be put to the test in clinical trials before being
adopted.
