Oocyte cryopreservation outcomes including pre-cryopreservation and post-thaw meiotic spindle evaluation following slow cooling and vitrification of human oocytes

ObjectiveTo report our oocyte cryopreservation (OC) outcomes including meiotic spindle (MS) evaluation of metaphase II (MII) oocytes destined for OC and thaw.DesignRetrospective.SettingUniversity-based infertility center.Patient(s)Women attempting pregnancy using cryopreserved oocytes.Intervention(s)OC, MS evaluation.Main Outcome Measure(s)Survival, two pronuclear (2PN) fertilization, achieving embryo quality suitable for transfer or refreezing, blastocyst formation.Result(s)Thirty-two OC-thaw cycles resulted in 20 pregnancies, 18 either ongoing or delivered. In 26 cycles, MS evaluation was performed: 262/303 (86%) thawed/recovered oocytes survived, 218/262 (83%) achieved 2PN fertilization, 133/218 (61%) became suitable for day-3 and 122/218 (56%) for day-5 transfer. In total, 58 embryos were transferred resulting in a 62% pregnancy and a 41% implantation rate. Of oocytes evaluated before cryopreservation, 247 (82%) were spindle-positive; 96% of these were also spindle-positive after thawing. Blastocyst formation and suitability for day-5 transfer was achieved more often if a post-thaw spindle was visualized. Of all slow-cooled and vitrified oocytes, a higher percentage of those slow-cooled achieved 2PN fertilization and usability. MS evaluation of oocytes cryopreserved by either method was associated with similar outcomes.Conclusion(s)OC outcomes are improving. An MS was almost always exhibited both before cryopreservation and after thawing, suggesting that, with appropriate technique, OC presents minimal harm to the MII oocyte. A meiotic spindle evaluation might help to further OC technology.