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.