Improved human oocyte development after vitrification: a comparison of thawing methods.

OBJECTIVE To evaluate the developmental competence of vitrified human oocytes thawed using two different methods to establish an effective cryopreservation protocol. DESIGN In vitro model study. SETTING University-affiliated hospital. PATIENT(S) Patients who underwent a long protocol of ovarian stimulation with GnRH and gonadotropins. INTERVENTION(S) Vitrified oocytes from the patients were thawed using either a four-step method with 2.5-minute intervals or a four-step method with 5-minute intervals. MAIN OUTCOME MEASURE(S) Morphologic normality, maturation, fertilization, and development of the oocytes to the blastocyst stage. RESULT(S) The two thawing methods did not significantly affect the morphologic normality (84%-100%), maturation (75%-100%), fertilization (38%-71%), polyspermy (more than three pronuclei; 0%-20%), or parthenogenetic activation (only female pronucleus; 0%-8%) of the vitrified oocytes. However, more of the vitrified oocytes developed to the two-cell (71%-100% versus 50%-67%), four-cell (71%-93% versus 0%-50%), eight-cell (46%-71% versus 0%), and blastocyst (23%-36% versus 0%) stages after thawing using the four-step method with 2.5-minute intervals than using the four-step method with 5-minute intervals. CONCLUSION(S) Vitrified human oocytes developed to the blastocyst stage with IVF. A four-step thawing method with 2.5-minute intervals was more effective in supporting preimplantation embryo development than a four-step thawing method with 5-minute intervals.