Failed cfDNA screen may signal increased risk of fetal aneuploidy
Findings from a recent study designed specifically to investigate the incidence of chromosomal abnormalities among high-risk pregnancies with a screen failure provide important information for patients and providers to consider when choosing follow-up.
Researchers found that the risk of fetal chromosomal abnormalities is increased significantly when noninvasive prenatal testing (NIPT) generates a “redraw request” (RR), and the risk is even higher if the repeat NIPT also fails.
The investigation analyzed results from cell-free DNA (cfDNA) screening performed from October 2012 to June 2014 in the Kaiser Permanente Northern California Regional Prenatal Screening Program and included NIPT draws in 4446 high-risk pregnancies. An initial result of RR was obtained in 102 (2.3%) pregnancies; of those women, 39 declined another NIPT and 63 chose to redraw. Almost half of the women who had a second test had another RR result (41%), while the outcome was low risk in 32 (51%) women and high risk in 5 women (8%).
Of the 65 women with no results after 1 or 2 tests, 43 (66.2%) had no chromosomal analysis, 13 (20%) had normal chromosomes, and 9 (13.8%) had abnormal chromosomes. The rate of chromosomal abnormalities was similar whether the failed test was due to high variance in cfDNA counts (15%) or insufficient fetal cfDNA (13%).
Chi-square analysis showed the incidence of chromosomal abnormalities was significantly higher for the subgroup of women with no results after 1 or 2 tests compared with the overall cohort (13.8% vs 2.4%; P=0.0001). Additionally, when compared to the overall cohort, the risk of finding a chromosomal abnormality was increased 2.5-fold among women who had 1 failed NIPT (P=0.0001) and 4.6-fold for those with 2 failed tests (P=0.0003).
Mary Norton, MD, a co-author of the study and Professor and Vice Chair, Clinical and Translational Genetics, University of California San Francisco, noted that at her institution, a repeat the cfDNA screen is offered to high-risk women who have a failed test. Taking into account the results of the Kaiser study, such women are also counseled that they are at increased risk of having a fetus with a chromosomal abnormality and so, might choose to have diagnostic testing with either chorionic villus sampling or amniocentesis instead. Ultrasound, however, may also be a reasonable option as initial follow-up testing in some cases, noted Dr. Norton.