The maturity of human cumulus-free oocytes is positively related to blastocyst development and viability.

PURPOSE: We investigated whether the human oocyte maturity at the removal of cumulus/corona cells affects the embryo outcome in vitro. METHODS: A total of 620 oocytes, which subsequently underwent blastocyst culture, were included in this analysis. Oocytes that were in prophase or Metaphase I of meiosis at the removal of cumulus/corona cells were in Group II. Oocytes that were in Metaphase II at the removal of cumulus/corona cells were in Group I. RESULTS: Group I oocytes yielded the highest fertilization rates (96.3% vs. 77.1%, P < 0.001). The incidence of Group II oocytes developing to the blastocyst stage was significantly less than from Group I oocytes (38.1% vs. 86.1%, P < 0.001). The percentage of top-scoring blastocysts from Group I oocytes was higher than that of Group II oocytes (95.4% vs. 76.2%, P < 0.001). CONCLUSIONS: Oocyte maturity at the removal of cumulus/corona cells needs to be considered in selecting good quality blastocysts for embryo transfer.