“…However, despite of high survival rates, vitrified M-II stage oocytes generally show poor developmental competence in terms of blastocyst formation rates and cell numbers in blastocysts [18]. Furthermore, most studies describing blastocyst production from vitrified porcine M-II stage oocytes used parthenogenetic activation to generate embryos [23, 28,[37][38][39], whereas other studies using IVF often reported the failure of embryo development [21,[40][41][42][43]. Similarly, in our laboratory, we have succeeded in the generation of blastocysts from vitrified M-II stage oocytes by parthenogenetic activation [25], whereas IVF of the M-II stage oocytes vitrified by the same method did not result in blastocyst development [27].…”