Series of tests detect Down's better, sooner
By Associated Press
Published October 9, 2003
A new combination of blood tests and ultrasound can detect fetuses with Down's syndrome sooner and more accurately than standard U.S. screening tests, offering mothers-to-be more peace of mind and more time to decide whether to end a pregnancy, researchers say.
The study of 8,216 women at a dozen U.S. medical centers confirms findings in England and elsewhere, where the combination is already widely used.
"It's earlier by about a month, so we've moved the standard testing to the first trimester and improved its accuracy," said lead researcher Ronald Wapner, chairman of obstetrics and gynecology at Drexel University College of Medicine in Philadelphia. "The absolute biggest advantage is this allows women to make private decisions" before they are visibly pregnant.
The usual blood screenings done in this country identify up to 75 percent of Down's syndrome babies, but do not yield results until about 20 weeks into pregnancy, when abortion is more dangerous for women and often difficult to obtain.
The new combination - two blood tests, ultrasound and the mother's age - correctly identified 85 percent of fetuses with Down's syndrome and yielded results at about 12 weeks.
Nine percent of the time, it incorrectly indicated a fetus probably had Down's syndrome.
About one in 800 babies has Down's syndrome, the most common chromosomal birth defect. Children with the syndrome suffer mental retardation and deformities such as a broad, flat face, short hands and a small head and ears.
When the four indicators together show a high probability of Down's syndrome, women can choose a definitive - and invasive - test. In chorionic villus sampling, cells are withdrawn from the placenta with a needle, usually at 10 to 12 weeks of pregnancy. In amniocentesis, which is more commonly done in this country, fluid is drawn from the amniotic sac with a needle; it is done at 14 weeks or later. Both techniques carry about a 1 percent risk of miscarriage.
The study was reported in today's New England Journal of Medicine.
In Tampa, the new test may give peace of mind to more women without taking the riskier invasive tests, said Dr. Catherine Lynch, associate professor and director of the division of general obstetrics and gynecology at the University of South Florida.
But she expects a negative reading on this test won't be enough for all patients.
"For someone who absolutely wants to know, 100 percent, they still would have to have chorionic villus sampling or amniocentesis," she said. "Otherwise, this gives a pretty good level of confidence that everything is okay."
The advanced testing likely won't be available for everyone in Tampa immediately, Lynch said. High-risk centers, such as at Tampa General Hospital, have ultrasound sonographers who already can perform the ultrasound that the researchers used. But others probably will need more training first, she said.
"It'll probably be a little time yet before it's mainstream," Lynch said.
Dr. Mark I. Evans, director of the Institute for Genetics and Fetal Medicine at St. Luke's's/Roosevelt Hospital Center in New York, said the study will cause a gradual shift from second-trimester screening to this method.
"There have been literally hundreds of thousands of patients evaluated worldwide who confirm these data," said Evans, president of the Fetal Medicine Foundation of America. "It's being routinely used all over the United Kingdom, Israel, Brazil and many other countries."
But in an accompanying editorial, Drs. Michael T. Mennuti and Deborah A. Driscoll of the University of Pennsylvania School of Medicine wrote that second-trimester screening should continue to be the standard until detailed guidelines can be developed for using the ultrasound and other tests.
Because mothers 35 or older have a higher risk of having a Down's syndrome baby - one chance in 270 - most get one of the invasive tests.
In addition to looking at the mother's age, the screening combination tested by Wapner and colleagues looks for low levels of a protein called pregnancy-associated plasma protein A, and for high levels of a type of the hormone human chorionic gonadotropin. The ultrasound test looks for telltale high levels of fluid in the fetus' neck.
Evans, who has researched the ultrasound test and been using it for a decade, said it is the single best marker of Down's syndrome. But he also warned that correctly reading the ultrasound requires specialized training and experience. It is available at some U.S. academic medical centers.
- Times staff writer Lisa Greene contributed to this report.
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