Not everybody is a big fan of being poked with needles to have their blood drawn. But from a medical perspective, blood tests are far less invasive and carry less potential for harm than other diagnostic tools. That’s why medical researchers are increasingly hunting for reliable blood tests for serious diseases, like the experimental Alzheimer’s disease test we covered last week. And this week, researchers report progress on assessing a new condition: a promising blood test for determining Down syndrome in a fetus.

The technique involves a blood test for the mother and an ultrasound for the baby. From the combined results, doctors can estimate the chance that the baby has Down’s. [CBS News]

Down syndrome happens when a baby has an extra copy of chromosome 21. Because the fetus’ DNA can cross over into the plasma of the mother, doctors can seek out the extra chromosome in a blood sample taken from the mother.

The researchers reporting in the British Medical Journal say that in a pool of 753 women, their tests had no false negatives. It accurately found all 86 fetuses with Down (The women selected were all at high risk for down in their fetus; the prevalence among the general public is only about 1 in 800). That’s a larger pool of women sampled than in similar research we covered in 2008, and with a higher success rate. The test is not perfect, though: It also identified false positives for Down in 2 percent of the fetuses that did not have the syndrome, which is why even a test more accurate than this one must have a backup to verify positive results.

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Two separate groups of researchers have developed a non-invasive test for Down syndrome, using only a blood sample from the pregnant woman to examine the fetus’ DNA. While the genetic tests are still in clinical trials, experts are hailing the achievement as significant because current prenatal tests like amniocentesis require inserting a needle in the uterus, and carry a risk of miscarriage.

A biotechnology company called Sequenom says it will begin selling its test next June, while researchers from Stanford, who just published their results in the Proceedings of the National Academy of Sciences, are still planning a large-scale clinical trial. Some experts say that the results are somewhat preliminary, and should be viewed cautiously: The Stanford test has been tried on only 18 blood samples. Sequenom has tried its test on only about 400 samples and has not yet published its results in peer-reviewed journals. Still, both tests have perfect records so far: no false negatives or false positives. “This is quite simply a major step forward, if it works at all like we expect it might,” [says Down Syndrome expert] Jacob A. Canick [The New York Times].

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