12. EMBRYOS FROM THE SAME COHORT SHOW HIGH VARIABILITY IN THE MTDNA LEVELS

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Introduction Mitochondria play a vital role in cell function. Recently, there has been an increasing research on mtDNA as biomarker of embryo implantation. Reports showed that high levels of mtDNA in blastocyst are associated with low implantation potential. Based on the available evidence, it is unclear whether high levels of mtDNA is a constant feature in some group of women or it depends on each embryo, showing variability among sibling embryos from the same cohort. The aim of this study was to investigate the variability in the levels of mtDNA among sibling euploid embryos from the same cohort. Material and Methods A prospective non-selection study was performed from January 2018 to December 2018. We included 249 blastocysts biopsies from 89 couples who attended our clinic for PGT-A with oocyte donation and with at least two of their biopsied embryos diagnosed as euploid non-mosaic. The aneuploid testing was performed by NGS-Veriseq® (Illumina). The mtDNA analysis was performed once the embryo diagnosis was known using MitoSeek. Sequencing reads mapping to the mtDNA genome were extracted from bam files. The relative measure of mtDNA copy number was calculated by dividing the mtDNA reads by the nuclearDNA and subjected to mathematical correction factor according to the embryo genome. Given that the mtDNA content is dependent upon the number of cell division that preceded the biopsy, the mtDNA content was also corrected by a factor according to the day when the embryos were biopsied. Statistical analysis was performed using SPSSv20.0. Results In order to avoid confusion related to the oocyte quality we included only egg donation cycles, therefore the average maternal age at time of oocyte retrieval was 26± 4 years (range: 19.0–33.0). Overall, the mean average of mtDNA per genome was 0.0010±0.0008 (range: 0.0002-0.0039). We analysed the mtDNA within an embryo cohort. To evaluate the extent of the variability in the mtDNA among embryos from the same cohort we calculate the coefficient of variation, being the average 28.77%. Furthermore, each embryo was classified according to the mtDNA 10th-percentile which belongs. The mean difference in the 10th-percentile between the embryo with the higher and the lower mtDNA within a cohort was 30. This difference was not related with the age of the egg donor neither the male factor (p>0.05). Only 13.5% of patients showed no difference in the mtDNA content within the embryos from the same cohort. Conclusion Our results suggest high variability in the mtDNA content within euploid embryos from the same cohort. MtDNA could be used to predict reproductive potential amongst chromosomally normal embryos however the utility of quantifying mtDNA levels depend on the existence of variability among embryos from the same cohort. This study reports that mtDNA content is not a marker of prognosis amongst patients because it is variable among the embryos from the same cohort, thus mtDNA could be used as an additional marker of embryo competence and a tool for prioritize the euploid embryo to be transferred.