(HealthDay News) — Maternal plasma cell-free DNA (cfDNA) sequencing for trisomies 18 and 21 gives 5–10 fold higher positive predictive values than standard aneuploidy screening in a general obstetrical population, according to a study published in the February 27 issue of the New England Journal of Medicine.

Noting that cfDNA testing is already known to be effective in women at high risk of fetal aneuploidy, Diana W. Bianchi, MD, from Tufts University in Boston, and colleagues performed massively parallel sequencing of maternal plasma cfDNA from 1,914 pregnant women at low risk of fetal abnormalities. The authors sought to determine the accuracy of detecting fetal trisomies 21 and 18 compared with standard aneuploidy screening.

The researchers found significantly lower false positive rates for cfDNA testing compared with standard screening (0.3 vs. 3.6% for trisomy 21 and 0.2 vs. 0.6 percent for trisomy 18). cfDNA testing detected all cases of trisomy 13, 18, and 21, with a negative predictive value of 100%. Overall, the positive predictive values were significantly higher for cfDNA testing than standard screening (45.5 vs. 4.2% for trisomy 21 and 40.0 vs. 8.3% for trisomy 18).

“In a general obstetrical population, prenatal testing with the use of cfDNA had significantly lower false positive rates and higher positive predictive values for detection of trisomies 21 and 18 than standard screening,” Bianchi and colleagues conclude.

Several authors disclosed financial ties (including employment) to Illumina, which supported the study.

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