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The Cell-Free Way

Noninvasive prenatal testing of cell-free fetal DNA isolated from maternal blood performed better than standard biochemical serum screening methods for detecting fetal aneuploidies, as fewer false-positive cases were reported, researchers from Tufts Medical Center, Illumina, and elsewhere write in the New England Journal of Medicine this week.

The researchers collected blood samples from some 2,050 women with singleton pregnancies at 21 different medical centers in the US. Those samples were blinded and sent for cfDNA analysis at Illumina, which funded the work. Of those women, about 1,910 also underwent standard screening.

As GenomeWeb Daily News notes, the researchers uncovered eight aneuploidies in the fetal DNA — five instances of trisomy 21, two cases of trisomy 18, and one instance of trisomy 13, using the sequencing-based approach. Additionally, 18 samples yielded no results. Results were verified either by chromosomal karyotyping or birth outcomes.

The DNA-based test, the researchers calculated, had a 0.3 percent false-positive rate for predicting trisomy 21 and a 0.2 percent false-positive rate for predicting trisomy 18. The conventional approach, meanwhile, had a 3.5 percent false-positive rate for predicting trisomy 21 and a 0.6 percent false-positive rate for predicting trisomy 18.

These results indicate that all women, not just those with high-risk pregnancies, could be offered such tests, researchers say.

"The current testing scares the wits out of a very large number of women, relatively speaking, who when they go through further testing are found to have totally normal fetuses," Michael Greene, the chief of obstetrics at Massachusetts General Hospital and who wasn't involved in the study, tells the Los Angeles Times. "With this new test, the number of women who get inappropriately or improperly labeled as having an abnormal fetus is very small. So that's a major advantage."

Other companies, including Natera, Ariosa Diagnostics, and Sequenom, offer similar cfDNA tests to detect fetal aneuploidies.