New Down syndrome testing may aid diagnosis
Friday, November 16, 2001
LONDON -- Using ultrasound to look for the nose bone in early pregnancy could help to identify Down syndrome babies sooner, new research suggests.
Some experts say the test, described for the first time this week in The Lancet medical journal, could be a major step forward, bringing the detection rate of Down syndrome screening up from about 65 percent today to about 98 percent, and allowing diagnosis in the first trimester rather than in the second, when the condition is normally confirmed.
Because the method has a lower false positive rate than current screening tests, it could also reduce the number of women having to undergo unnecessary diagnostic tests, which involve inserting a needle into the womb and trigger miscarriages about 1 percent of the time, experts said.
"Adding the nasal bone test is a big leap forward," said Dr. Howard Cuckle, professor of reproductive epidemiology at Leeds University in England, who was not connected with the study.
However, other obstetricians said that while the findings were impressive, detecting a nasal bone on an ultrasound requires special skills and it would be difficult to maintain quality measurements everywhere.
Early screening rare
"In the U.S., we are still not fully using first trimester screening, partly due to insurance reimbursement issues -- most health insurers pay for only one routine sonogram," said Dr. Joshua Copel, chief of maternal fetal medicine at Yale University School of Medicine.
Doctors are also waiting for the results of a major U.S. study comparing first- and second-trimester screening techniques, he said.
One of every 700 children is born with Down syndrome, a chromosomal abnormality that is a common cause of mental retardation and is marked by a broad, flat face with slanting eyes.
The condition is caused by having three Chromosome 21s, instead of two.
Prenatal diagnosis is made by one of two tests that analyze chromosomes in cells taken from the mother's belly with a needle.
The most popular test is amnioscentisis, which draws out amniotic fluid during the second trimester of pregnancy.
The other, which is most widely used in Europe, is chorionic villus sampling, or CVS. The CVS test extracts a sample of the placenta and is performed during the first trimester.