Association of mitochondrial DNA content and embryo morphology in fully expanded euploid blastocysts

Over the past two decades, mitochondrial DNA (mtDNA) content has been studied as a potential biomarker for embryo viability and implantation success during in vitro fertilization (IVF) procedures. However, its reliability for embryo selection remains uncertain. Therefore, our study aimed to examine the relationship between blastocyst mtDNA content and blastocyst quality, timing of fully expanded blastocyst formation, and cleavage-stage embryo quality in blastocysts biopsied at the uniform expansion stage. We analyzed bioinformatics data from 125 day-5 and day-6 blastocysts from women aged 18 to 35 years. Each blastocyst was biopsied at expansion stage 4 and classified as euploid through preimplantation genetic testing for aneuploidy using next-generation sequencing. Blastocysts were categorized into four groups based on quality and the day of biopsy. Poor-quality day-6 blastocysts exhibited lower mtDNA levels compared to good-quality day-5 blastocysts (<i>p</i> = 0.006), poor-quality day-5 blastocysts (<i>p</i> = 0.008), and good-quality day-6 blastocysts (<i>p</i> = 0.003). Embryos with day-3 grades lower than 2.5 displayed lower blastocyst mtDNA levels compared to those graded 1 (<i>p</i> < 0.001), 1.5 (<i>p</i> < 0.001), and 2 (<i>p</i> < 0.001). These findings suggest further insights into the interplay between blastocyst mtDNA content and preimplantation embryo morphology. Nonetheless, mtDNA remains an unreliable biomarker for assessing embryo viability, warranting further investigation to determine its clinical relevance.