Fast and furious: successful survival and resumption of meiosis in immature human oocytes vitrified and warmed using a short protocol

RESEARCH QUESTION Can immature oocytes vitrified and warmed using a short protocol survive and resume meiosis? DESIGN This study examined modifications of oocyte vitrification and warming protocols that shorten the time of exposure to vitrification and warming solutions. A total of 561 germinal vesicles (GV), and 218 metaphase I (MI) oocytes that were immature at oocyte retrieval were vitrified at room temperature in 2 minutes. Warming was done at 37°C in 2 minutes. Resumption of meiotic activity was evaluated after 24 and 48 hours of culture. Two different commercially available vitrification and warming kits were used for comparison. RESULTS Ninety five percent of GV oocytes survived with no difference observed between kits. The survival of MI oocytes was on average 95.4% and not significantly different between the two kits. Of the 533 GV that survived, 491 converted to MI (92.1%). After culture for 48 hours, 54.4% converted to MII oocytes. In addition, of the 208 MI that survived the warming, 84.1% converted to MII oocytes after culture for 24 hours. CONCLUSIONS Vitrification and warming of oocytes at different nuclear maturation stages can be done with a 2-minute exposure time to hypertonic and a 2-minute exposure time to hypotonic solutions. With this approach, the oocytes are less exposed to room temperature during dehydration and rehydration. Warming in 0.5M sucrose helps to maintain and support the potential to resume nuclear meiotic activity of oocytes and conversion from GV to MI and to MII oocytes.