The usual blood screenings done in this country identify up to 75 percent of Down 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 syndrome and yielded results at about 12 weeks.
Nine percent of the time, it incorrectly indicated a fetus probably had Down syndrome.
About one in 800 babies has Down 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 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 In chorionic villus sampling, cells are withdrawn from the placenta with a needle, usually at 10 to 12 weeks of pregnancy.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.
Dr. Mark I. Evans, director of the Institute for Genetics and Fetal Medicine at St. Luke'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, doctors 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.
