WASHINGTON Oct 6 A prenatal blood test can be used to determine if an unborn baby has Down's syndrome without the small risk to the fetus posed by invasive testing methods such as amniocentesis, U.S. researchers said on Monday.
Researchers led by Stephen Quake of Stanford University in California created a way to look for the extra chromosomes that cause Down's and similar birth detects in the tiny amounts of fetal DNA that circulate in the mother's blood.
The test, which requires a small blood sample from the mother, is safer than amniocentesis, in which a needle is stuck into the uterus, and can be done earlier in a pregnancy.
Down's syndrome, which causes mental retardation and other problems, is caused when a child has three copies instead of the normal two of chromosome 21.
The test also detects other chromosomal conditions such as Edward syndrome, which kills half of babies in the first week of life and Patau syndrome, which kills more than 80 percent of children in infancy.
Quake's team demonstrated the accuracy of the new genetic test in a small study involving 18 women.
It accurately identified the nine women with a Down's syndrome pregnancy and three others with fetuses with different chromosomal disorders, the researchers wrote in the journal Proceedings of the National Academy of Sciences.
"It's the first universal, noninvasive test for Down syndrome. So this should be the first step in putting an end to invasive testing procedures like amniocentesis and chorionic villus sampling," Quake said in a telephone interview.
Blood tests for pregnant women like the alpha-fetoprotein test can find potential signs of a chromosomal disorder such as Down's, but cannot diagnose it with certainty.
Quake said such tests serve as only "indirect and weak predictors of what's going on."
For a definitive determination, women must have an invasive diagnostic procedure such as amniocentesis or chorionic villus sampling. This is done typically after the 15th week of pregnancy.
These procedures carry a small risk -- roughly 1 percent -- of causing a miscarriage or birth defects.
Because of that, their routine use has been mostly by women age 35 and older at higher risk for having Down's syndrome babies. Scientists have been working for years to devise safer, noninvasive tests suitable for any pregnant woman.
Quake said the new test also could be administered much earlier in a pregnancy than amniocentesis or CVS -- potentially as early as five weeks after conception. And the results are back within a couple of days, instead of two to three weeks.
Some women terminate the pregnancy when they learn the fetus has Down's syndrome but others, including Republican U.S. vice presidential candidate Sarah Palin, do not.
Quake said the new test could be widely available in two or three years, and could become a routine prenatal test of a baby's health. Quake said the next step is a larger study involving hundreds of women.
Stanford University has filed a patent on the test and two companies are negotiating for the licensing rights, Quake said. He said he is has been hired as a consultant for both companies, which he declined to identify.