Effects of ovarian hyperstimulation on mitochondria in oocytes and early embryos

A mouse model was used to compare the number and function of mitochondria in oocytes and embryos obtained by superovulation and in a natural cycle (control group). The superovulation group had a higher number of total oocytes, MII oocytes, embryos with two pronuclei, 2-cell embryos and blastocysts than the control group (P < 0.05 for all). The superovulation group had high proportion of MII oocytes with low number of mitochondrial (mt) DNA copies. The average number of mtDNA copies, ATP level and mitochondrial membrane potential (??m) in MII oocytes in the superovulation were lower than in the control group (P < 0.05 for all). However, at the blastocyst stage, mean mtDNA copies, ATP level and ??m did not differ significantly between the two groups. These results suggest that ovarian hyperstimulation does not cause damage to the mitochondria in eggs but, rather, more eggs with poor mitochondrial quality are recruited, resulting in a decline in average mitochondrial quality.