The present study has the objective to study whether the mitochondrial DNA copy number values that can be generated when human embryos are analyzed for chromosomal content before embryo transfer correlates with the actual number of mitochondria as well as their energy requirements of the human embryo.

The possibility of analyzing trophectoderm cells from human blastocyst during preimplantational genetic testing offers the opportunity of analyzing not only the chromosomal constitution of the trophoblastic cells, and by extension, to infer not with certain degree of uncertainty, the chromosomal content in the inner cell cells mass and the entire embryo; but analyzing other interesting aspects related to cellular physiology such us the mtDNA content.

The number of mitochondrial copy number has a huge variation among oocytes from the same cohort and also from oocytes from different patients. It is believed that this initial number of mtDNA content is correlated with the ability of oocytes to fertilized and to achieve blastocyst stage. Whatever the initial concentration of mtDNA a given oocyte will have, it expected to equally segregate into the number of blastomeres along embryo development, so the mtDNA copy number of per daughter cell will transiently decrease, being the smallest at the blastocyst stage. Studies in different mammalian species including humans have shown that mtDNA replication does not occur before morula stage so the mitochondrial content of the oocytes should be enough to sustain embryo development before implantation occurs.

The net amount of mitochondrial DNA will exponentially increase at blastocyst stage coinciding with an increases in oxygen consumption. Despite the mtDNA copy number is higher in ICM compared to TE cells the proportion of moderate and high activity mitochondria is higher in the TE cells. This also agrees with mitochondrial morphological changes in the trophectoderm cells where mitochondria are much more elongated, less matrix electrodense and have more cristae, in ICM the will be rounded and more electrodense.

The objective of the present work is to analyze whether a correlation exist between the mitochondrial DNA copy number and both the actual number of mitochondria in the blastocyst and the metabolic needs of the human blastocysts and the ATP production.

Inclusion Criteria of women whose blastocysts will undergo PGT-A and be eligible for study:

• > 38 years old
• Sperm count: > 2 million spermatozoids/ml
• Oocytes retrieved > 4 oocytes MII
• Antral Follicles (AFC: ≥4)

Blastocysts from women undergoing PGT-A and available for analysis )