Screening fetuses for Down Syndrome is now more effective, accurate, safer, and faster, thanks to a new test that analyzes fetal DNA that is found in a pregnant woman's blood.
A genetic test, currently being marketed by Illumina Inc. of San Diego, California, which also funded the research, was studied by a team of researchers and was proven to yield much fewer false positives in the 1,914 women tested, compared with the standard serum screening, even as early as 10 weeks into the pregnancy.
The findings of the study were published in the New England Journal of Medicine. The test is called the cell free DNA test, or cfDNA, and works by looking at small amounts of actual fetal DNA floating freely in the mother's blood. The study analyzed blood samples collected from 21 centers in the United States, from a total of 1,914 pregnant women with a mean age of 29.6 years who were undergoing standard screening for aneuploidy, a condition in which one or more missing chromosomes can signal the possibility of the unborn baby eventually being born with Down Syndrome. Then the results from the standard screening were compared with the results from the cfDNA test.
The study has found that, on top of the greatly reduced number of false-positive results, the cfDNA test performed 10 times better than other noninvasive tests currently available in screening for Down Syndrome, and was 5 times better in predicting the presence of Trisomy 18, another disorder.
The test was correct 45.5 percent of the time in predicting Down Syndrome, which is much higher compared with the performance of the standard screening test, which was correct only 4.2 percent of the time. The test was also accurate in predicting Trisomy 18 almost 41 percent of the time, whereas the standard screening was correct only 8 percent of the time.
Diana W. Bianchi, executive director of the Mother Infant Research Institute at Tufts Medical Center in Boston, who headed the study, explained that this could mean good news for women who would have to undergo invasive tests like amniocentesis or chorionic villus sampling, just to confirm results yielded by the standard blood test.
"Nine out of 10 women who are currently being referred for further testing would not need invasive tests," said Dr. Bianchi, who is also a paid advisory board member of Illumina, Inc.
"The major advantage of using cfDNA testing was the reduction in rates of false positive results. A consideration of cost-effective ways to incorporate cfDNA testing into general obstetrical practice is beyond the scope of this study. Our findings, however, suggest that cfDNA testing merits serious consideration as a primary screening method for fetal autosomal aneuploidy," the research concluded.
Some eyebrows were raised at the connection between Illumina, Inc., Dr. Bianchi, and the study. Dr. Michael Greene, director of obstetrics at Massachusetts General Hospital an associate editor at The New England Journal of Medicine, said that the study could have been "purer" from an academic perspective if Illumina, Inc. was not the one who paid for it, but he also said, "We can't have our cake and eat it too."
He also clarified that the New England Journal of Medicine considered this study to be well done, whereas it had rejected other studies on cell-free DNA.
