Suboptimal trophectoderm mitochondrial DNA level is associated with delayed blastocyst development.

Our data provided further evidence D5 blastocysts contained significantly greater mtDNA quantity than D6 blastocysts, and mtDNA quantity could be a key factor that affects the development rate of blastocysts. Furthermore, one must avoid using an arbitrary threshold when incorporating mtDNA quantity into the embryo selection criteria, as the observed value may have vastly different clinical implication when blastulation rate is also considered.