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MG-145 Importance of fetal fraction analysis for CFDNA testing in the general pregnancy population
  1. Eric Wang,
  2. Craig Struble,
  3. Christopher Kingsley,
  4. Rhoberta Steeke,
  5. Annette Batey,
  6. Desiree Hollemon,
  7. Arnold Oliphant,
  8. Thomas Musci
  1. Ariosa Diagnostics


Background Harmony™ Prenatal Test uses an assay method, Digital Analysis of Selected Regions (DANSR™), for analysis of chromosomes 13, 18, 21, X and Y as well as other chromosomes to measure fetal fraction (FF). Products from the DANSR assay are then analysed with Fetal fraction Optimised Risk of Trisomy Evaluation (FORTE™) algorithm to assess patient-specific risk of trisomy. Alternative tests, such as those using massively parallel shotgun sequencing, use a Z-statistic or Normalised Chromosome Value (NCV) to discriminate between normal and abnormal chromosomal counts without accounting for FF.

Methods A general pregnancy population cohort of 15,841 women between 10.0 to 14.3 weeks gestation were followed to pregnancy outcome. Z-statistics were computed using previously described standard Z-test of proportions and compared to FORTE risk scores generated by Harmony. A Z-statistic of ≥3 was ‘Positive’ for trisomy and a FORTE risk score of ≥1% was ‘High Risk’ for trisomy.

Results See Table 1. Cumulative test discordant rate for non-trisomies with FORTE was 0.08% compared to 1.07% with Z-statistic.

Abstract MG-145 Table 1

PPV: Positive Predictive Value

Conclusion Analysis using FORTE to incorporate FF in cfDNA testing yields >10 fold reduction in discordant results This will become increasingly relevant as cfDNA testing gets more broadly used in the general pregnancy population.

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