Whilst considerable focus has been on nuclear-encoded and enzymatic markers as indicators of developmental competence and good quality embryo production, the mitochondria and the mitochondrial genome have much to offer. Assessment of oocyte mtDNA copy number can be determined for women who have suffered from repeated failed fertilisation or embryonic developmental failure. This can be performed by directly assessing mtDNA copy number in failed to fertilise oocytes (73) or indirectly by assessing cytoplasmic volume following superovulation where a direct correlation between mtDNA copy number, oocyte volume and fertilisation outcome have been observed (72, 78). Likewise, the quality of the mitochondria, namely punctate mitochondria indicative of good quality mitochondria (Figure 13), could be assessed (10). For those embryos that undergo developmental arrest, assessment of mitochondrial shedding can be assessed by assaying the amount of mtDNA that is present in the embryo culture media at various stages of preimplantation development (42). Failure for this process to take place would be indicative of the lack of interaction between the nucleus and the cytoplasm to mediate the reduction in mtDNA copy number or insufficient mtDNA copy present to support this outcome.

Arrested embryos can be assessed for mtDNA copy to ascertain whether copy number or the regulation of copy number is the issue. Similarly, assessment of mtDNA copy in supernumerary blastocysts could provide significant indications as to whether effective regulation of copy number in the trophectoderm and the inner cell mass has taken place. Analysis of the trophectoderm alone will not provide this outcome as it is not indicative of the inner cell mass, which requires significant reduction in mtDNA copy number to establish the set point, as described above (21, 40, 82). Nevertheless, assessment of trophectodermal mtDNA copy number might indicate the ploidy of the embryo and implantation success (88).