WEDNESDAY, Nov. 9 (HealthDay News) -- In what a team of scientists says is a first, the researchers appear to have successfully screened for a rare form of fetal abnormality by means of a completely noninvasive blood test.

By performing a DNA analysis on a blood sample from a prospective mother, the team was able to accurately identify a specific chromosomal irregularity called "fetal microdeletion syndrome" in the unborn child, reported investigators at the Magee-Womens Research Institute (MWRI) at the University of Pittsburgh Medical Center.

In so doing, the researchers indicated it may one day be possible to avoid the use of much more invasive -- and thereby riskier -- standard diagnostic techniques, such as amniocentesis.

"If a fetal anomaly is suspected, mothers are usually offered an invasive screening procedure," said David Peters, head of the MWRI team and an associate professor in the department of obstetrics, gynecology and reproductive sciences.

"But there is a pretty significant, if small, level of risk to the health of the fetus associated with those tests. So there's been a strong push to try and reduce that risk," he noted.

"So I think the most compelling point," said Peters, "is that we have been able to illustrate a proof of concept. We have shown that you can identify these sorts of abnormalities without having to collect a physical sample from the baby or the placenta."

Peters and his colleagues discussed their findings in a letter published in the Nov. 10 issue of the New England Journal of Medicine.

Although this may be the first such test for this particular type of defect, maternal blood tests are also being developed for other fetal anomalies such as Down syndrome, as reported by HealthDay earlier this year. That study, conducted by Greek researchers, was published in the March 6 online edition of Nature Medicine.

According to the March of Dimes, roughly one in every 150 American babies is born with a structural or numerical chromosomal abnormality.

Such abnormalities can develop during egg or sperm cell growth, both before and after conception. Oftentimes they give rise to severe mental or physical defects, including Down syndrome and spina bifida.

Typically, chromosomal abnormalities are first identified during pregnancy by invasive diagnostic procedures.

Chorionic villus sampling is one option, involving the extraction of cellular material found in tiny finger-shaped growths located in the placenta. The procedure requires a catheter or long needle, and is usually conducted in the latter part of the first trimester.

The other option is amniocentesis, involving the extraction of a small amount of amniotic fluid surrounding the fetus for subsequent DNA analysis. The procedure is usually performed during the second trimester, and entails the use of a local anesthetic and the insertion of a needle through the mother's abdominal wall, uterus and amniotic sac.

But these invasive methods involve some risk, as fetal limb damage, fetal respiratory distress and even miscarriage can occur as a result.

To explore the potential of a less-invasive screening tool, the MWRI team focused on a couple who had already previously had a child born with physical and developmental abnormalities. In that case, the culprit was the absence (or "deletion") of specific chromosomal DNA, a condition that the child had inherited from his father.

At 21 weeks into her current pregnancy, the mother underwent traditional amniocentesis, which confirmed that her unborn child also suffered from the same rare fetal microdeletion syndrome.

In turn, at 35 weeks into the pregnancy the team drew a maternal blood sample and conducted a series of high-tech genetic sequencing tests. This time, no fetal tissue or blood was extracted.

The result: The non-invasive blood test successfully arrived at the same diagnosis as the invasive amniocentesis.

Peters acknowledged that the 35-week mark is late for prenatal screenings, but added that the time frame was appropriate for a comparative analysis of a new screening approach that is still in its infancy.

"I'm not a clinician, but I think it's fair to say that at this point we're a long way away from having something that would practically be able to replace amniocentesis," he cautioned.

Dr. De-Kun Li, a reproductive and perinatal epidemiologist in the division of research at Kaiser Permanente Northern California, in Oakland, said that while the risk associated with invasive screening is very low, an equally accurate risk-free blood test would be ideal.

"I believe the risk of spontaneous abortion or miscarriage due to an amniocentesis is 0.5 percent," he noted. "And the rate has been going down, because we are now much more technologically savvy. But of course a blood test would be noninvasive, cheaper and less risky. The question is, will the accuracy be the same? If so, then of course we'll go with the blood test. No questions asked. But that's a big 'if.'"

More information

For more on birth defects and chromosomal abnormalities, visit the March of Dimes.