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Interpreting Failed Results on NIPT

Interpreting Failed Results on NIPT

Noninvasive prenatal testing (NIPT) has become popular with many physicians in screening pregnant patients. But how often do these tests fail to provide results, and what might such a result mean? Researchers helped answer this question last week in San Diego at The Pregnancy Meeting, the Society for Maternal-Fetal Medicine’s annual meeting, when John Turocy, MD, presented research on the high rate of chromosomal abnormalities in patients in whom noninvasive prenatal testing fails to provide results.

To help answer these questions, researchers offered high-risk women (per ACOG guidelines) noninvasive prenatal tests, which were conducted at an outside laboratory between October 2012 and June 2014 as part of the Kaiser Permanente Northern California Regional Prenatal Screening Program. Test results were reported as low risk, high risk, or redraw request (RR) if no result was obtained. The incidence of chromosomal abnormalities in the RR group was compared with that of the entire cohort.

Noninvasive prenatal tests were performed in a total of 4446 pregnancies. Of those, 102 (2.3%) resulted in an initial result of RR, with 63 of the women choosing to redraw the test and 39 declining. Of the 63 women who were retested, 32 (51%) were low risk, 5 (8%) were high risk, and 26 (41%) once again received the result RR.

Overall, a total of 65 (1.5%) of the 4446 tests had no final result after either one or two blood draws, 4219 (94.9%) had low-risk results, and 162 (3.6%) had high-risk results. Of the 65 women whose test failed to yield a result, 43 (66.2%) opted for no chromosomal analysis, 13 (20%) discovered their fetus had normal chromosomes, and 9 (13.8%) learned their baby had chromosomal abnormalities (3 had triploidy, 3 had T18, 1 had T13, 1 had T20, and 1 had 45,X). In cases where results were not obtained because insufficient fetal cfDNA, 7 (13%) of 52 had abnormal chromosomes. In cases with no result because of high variance in cfDNA counts, 2 (15%) of 13 had abnormal chromosomes.

The rate of chromosomal abnormalities in patients with no final result was significantly higher than the rate of chromosomal abnormalities in the overall cohort (9 [13.8%] of 65 vs 108 [2.4%] of 4446, respectively; P=0.0001.

These findings show that there tends to be a high rate of chromosomal abnormalities on repeat testing after a failed NIPT result. In addition, nearly half of tests again will fail on subsequent NIPT attempts.

“This is important information for patients and providers and requires clear understanding on how to interpret test results and appropriate follow-up,” explained Turocy.

Turocy J, Norem C, Blumberg B, et al. Chromosomal abnormalities detected in patients with failure to obtain test results using non-invasive prenatal testing. Abstract no 65. Presented at: The Pregnancy Meeting, the Society for Maternal-Fetal Medicine’s annual meeting; February 6, 2015; San Diego, Calif.

 
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