Embryo developmental capability and pregnancy outcome are related to the mitochondrial DNA copy number and ooplasmic volume.

Purpose: To investigate the correlation between the ooplasmic volume and the number of mitochondrial DNA (mtDNA) copies in embryos and how they may affect fecundity.

Method: Using real-time PCR, mtDNA quantification was analyzed in unfertilized oocytes and uncleaved embryos. The size of the ovum was also assessed by calculating the ooplasmic volume at the time of granulosa cell removal for IVF or ICSI. Quantification analysis of the mtDNA in blastomeres was performed by real-time PCR at the 7-8 cell stage of the cleaved embryos at 72 h after oocyte retrieval. We calculated the cytoplasmic volume of the blastomeres.

Result: Our studies showed a significantly lower mtDNA copy number in unfertilized oocytes and uncleaved embryos in women who were older than 40 years of age (p < 0.05). The larger ooplasmic volume was also associated with earlier and more rapid cleavage (p < 0.05). The ooplasmic volume was also significantly larger in the group achieving pregnancy. We found a significant positive correlation between blastomere volume and the number of mtDNA copies (r = 0.76, p < 0.01, from Pearson product-moment correlation coefficient).

Conclusions: We have shown that blastomere volume is directly proportional to the number of mtDNA copies. Therefore, larger cytoplasmic volume, with earlier cleavage speed, implies more mtDNA copies. Evaluation of mtDNA quantification and the measurement of ooplasmic and blastomere volume may be useful for selection of high quality embryo and pregnancy outcome.