2. CLINICAL COMPARISON OF TWO PGT-A PLATFORMS UTILIZING DIFFERENT THRESHOLDS TO DETERMINE PLOIDY STATUS

Abstract

Introduction Unlike previous technologies that lack the diagnostic performance to reliably detect mosaicism for preimplantation genetic testing for aneuploidy (PGT-A), next generation sequencing (NGS) based platforms now allow for the detection of lower-level mosaicism. Due to this increased sensitivity, thresholds need to be put in place to classify embryos as euploid, aneuploid, or mosaic. The lower cutoff for mosaic samples ranges from 20 % to 30 %, and the upper cutoff for mosaic samples ranges from 70%-80% in most commercial PGT laboratories in the field today. These varying cutoffs will lead to varying percentages of mosaic embryos reported, suggested to be somewhere between 20 %. A more stringent threshold could result in greater pregnancy rates. Here we compare clinical outcomes and embryo reporting between two different PGT-A reference laboratories that use different testing platforms and different mosaic cutoffs. Materials and Methods Retrospective analysis of PGT-A results (n=623) and frozen embryo transfer (FET) cycles (n=99) using embryos diagnosed by either Cooper Genomics or Igenomix between January 2018 - January 2019. Cooper Genomics uses Illumina's MiSeq platform with Bluefuse software and thresholds of 20% to 80 % (lower to upper cutoff) while Igenomix uses ThermoFisher's Ion Torrent platform with Ion Reporter software and thresholds of 30% to 70 %. Patients with a history of recurrent miscarriage were excluded from this study. Results Fifty six (56) cycles included embryos analyzed by Cooper Genomics and 43 cycles included embryos analyzed by Igenomix as a PGT-A reference laboratory. There was no differences in maternal age or number of embryos replaced per transfer between the two cohorts. IVF outcome was similar between the two groups: The pregnancy (+FHB) observed in cycles that transferred embryos diagnosed as euploid by Cooper Genomics was 67.9% (38/56) compared to 69.8% (30/43) with Igenomix. Miscarriage rate was also similar, 8.9% (5/56) and 6.9% (3/43) respectively. Cooper Genomics reported a much higher rate of mosaicism (17.0%) compared to Igenomix (4.9%) (p Conclusion Retrospective analysis of PGT-A+FET cycles revealed there was no differences in pregnancy or miscarriage rates indicating a similar diagnostic efficacy achieved by the two PGT-A platforms. Although the embryos diagnosed as euploid by the two platforms appeared to have the same potential to generate a pregnancy, the methodology and higher threshold utilized by Igenomix resulted in significantly less mosaic embryos and a slightly greater percentage of euploid embryos available for transfer. It is assumed that cumulative pregnancy rates between the two reference laboratories would vary based on the finding that there were more euploid embryos available from Igenomix. Results from subsequent FET cycles will be collected and further examined. NGS has now created three categories of embryos that exist after PGT-A, the interpretation of the millions of data points generated by this technology still remains a challenge and it is important that the diagnostic methodology used does not overestimate the degree of mosaicism.