Variables associated with mitochondrial copy number in human blastocysts: what can we learn from trophectoderm biopsies?

Objective: To study the potential variables that affect the mitochondrial DNA (mtDNA) content of trophectoderm (TE) cells in blastocysts that have undergone TE biopsy. Design: Observational retrospective single-center analysis. Setting: University-affiliated private in vitro fertilization center. Patient(s): A total of 465 consecutive preimplantation genetic screening (PGS) cycles of 402 women undergoing preimplantation genetic testing. Intervention(s): Trophectoderm biopsy performed on blastocysts of women undergoing preimplantation genetic testing-aneuploidy (PGT-A). Main Outcome Measure(s): The mtDNA content in trophectoderm cells. Result(s): We checked the possible influence of patient characteristics, ovarian stimulation variables, embryo morphology, and embryo culture conditions on mtDNA values. Of all the analyzed variables, some such as body mass index (BMI), serum progesterone (P4), aneuploidy, and trophectoderm quality had an effect on mtDNA content in blastocysts. Body mass index had a small but positive effect on the mtDNA copy number; as the BMI values increased, the probability of women producing blastocysts with an mtDNA content above the median increased by 6%. For P4 serum concentration, an increase in P4 lowered the probability of blastocysts having values above the median by 39%. Embryo-associated variables such as TE quality and aneuploidy status appeared to affect the mtDNA copy number. For the aneuploid blastocysts, the probability of being above the median increased by 42%. Finally, blastocysts with poor quality TE had more chances of carrying higher mtDNA values. Conclusion(s): Summarizing, larger quantities of mtDNA in blastocysts are associated with the condition of aneuploidy and low quality TE, as well as being from women with high BMI values. Understanding the biological meaning of mtDNA content in human blastocysts and what factors may interfere with their values is fundamental. Other key gaps, such as whether a correlation exists between mtDNA content and mitochondrial mass and biogenesis in human TE cells, and whether this correlation can be extended to the inner cell mass, need to be further addressed. These questions are currently being investigated. (C) 2017 by American Society for Reproductive Medicine.