A non-invasive blood test to determine if a fetus has Down syndrome early in pregnancy could be available in two or three years, researchers say.

The new test requires a small blood sample and can be done at an earlier stage of pregnancy than current tests, avoiding the roughly one per cent risk of miscarriage that comes with current prenatal tests that involve inserting a needle into the uterus.

In a small study appearing in this week's issue of the Proceedings of the National Academy of Sciences, Stephen Quake, a professor of bioengineering at Stanford University in California, described the test, which accurately identified nine cases of Down syndrome, three other fetuses with different chromosomal disorders, and six normal pregnancies.

People with Down syndrome carry an extra copy, or extra parts, of chromosome 21.

About half of infants with Edward syndrome or trisomy 18, who carry an extra copy or extra parts of chromosome 18, don't survive the first few weeks of life, and more than 80 per cent of children born with Patau syndrome or trisomy 13, who carry an extra copy or extra parts of chromosome 13, die in the first month.

"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. 

Current screening tests for pregnant women such as the alpha-fetoprotein blood test show potential signs of chromosomal disorders, but may miss five to 30 per cent of Down syndrome cases and carry a false positive rate of five per cent, which may lead women to unnecessarily undergo diagnostic tests such as amniocentesis or chorionic villus sampling.

The diagnostic tests are typically done after the 15th week of pregnancy, and involve sampling cells in amniotic fluid to count the number of chromosomes the fetus carries. It takes two to three weeks to get the results.

Quake said his approach uses a small amount of blood from a woman, can be done around 12 weeks, and results are available within a few days.

In the study, results from the 18 participants were matched to those from amniocentesis or CVS tests that were also done on the women.

Information should be fair, balanced: society

Quake is planning a followup study to evaluate the test in a larger group of women, at an estimated cost of about $300 US per test. Stanford has filed a patent on the test, and Quake works as a consultant for two companies that are negotiating licensing rights.

San Diego-based Sequenom Inc. is also working on a Down syndrome blood test using a different approach that has not yet been published in a peer-reviewed journal. The company is conducting a study on 10,000 subjects to verify its results. The test has a 99 per cent detection rate with no false positives, company officials say.

"It's highly likely that within the next two years, this test will be available to Canadian women and prospective families," said Krista Flint, executive director of the Canadian Down Syndrome Society in Calgary.

"We know that these medical advancements will continue, and we think information is terribly important to families. But we want families to receive fair and balanced information, not just about the challenges of a life with Down syndrome, but also the richly rewarding lives that are possible for citizens with Down syndrome."

In the U.S, it is estimated that 80 to 95 per cent of pregnancies with an early determination of Down syndrome will be terminated.

"I think we have to be honest about the fact that a determination of Down syndrome very early in a pregnancy is very likely going to be accompanied by pressure to terminate a pregnancy, and that's been the experience of most of the families that are connected to the Canadian Down Syndrome Society."

The group's 56 local chapters offer prospective and new parents the opportunity to meet with children with Down syndrome, as well as online information and printed brochures.

With files from Reuters