What Drives Embryo Development? Chromosomal Normality or Mitochondria?

OBJECTIVE To report the arrest of euploid embryos with high mtDNA content. DESIGN A report of 2 cases. SETTING Private fertility clinic. PATIENTS 2 patients, 45 and 40 years old undergoing IVF treatment. INTERVENTIONS Mature oocytes were collected and vitrified from two ovarian stimulations. Postthaw, survived mature oocytes underwent fertilization by intracytoplasmic sperm injection (ICSI). Preimplantation genetic screening (PGS) and mitochondrial DNA (mtDNA) copy number were done using next generation sequencing (NGS). The only normal embryo among the all-biopsied embryos had the highest "Mitoscore" value and was the only arrested embryo in both cases. Therefore, the embryo transfer was cancelled. MAIN OUTCOME MEASURES Postthaw survival and fertilization rate, embryo euploidy, mtDNA copy number, and embryo development. RESULTS In both patients, after PGS only 1 embryo was euploid. Both embryos had the highest mtDNA copy number from all tested embryos and both embryos were arrested on further development. CONCLUSIONS These cases clearly demonstrate the lack of correlation between mtDNA value (Mitoscore) and chromosomal status of embryo.