Vitrification is a method to cryopreserve biological specimens that are sensitive to chilling injury such as oocytes and embryos, and it has been employed with increased survival rate and live births (Hong et al., 1999; Kuleshova et al., 1999; Yoon et al., 2000; Chung et al 2000; Wu et al., 2001: Kuwayama et al 2006). In their study the researchers propose to directly compare oocyte survival, fertilizaton and embryo development between sibling oocytes.