P-248 The meiotic spindle is preserved during freezing but post-thawing rehydration causes its destabilization in human eggs

Abstract Study question Is the human egg spindle integrity impaired by vitrification and thawing procedures? Summary answer Cryoprotective-caused dehydration stabilizes MII spindle, but re-entry of water during induces depolymerization microtubules, thus promoting instability division apparatus. What is known already Freezing sperm preimplantation embryos have become routine IVF procedures with excellent clinical results, whereas cryopreservation oocytes remains problematic. The major factor underlying oocytés notorious propensity to cryoinjury temperature sensitivity meiotic fidelity which critical for faithful post-fertilization development. Most studies focus on evaluating vitrified-thawed oocytes' outcome, behavior freezing process has received only a little attention. design, size, duration experimental study involved total 165 donated research. presence morphology were examined polarized light microscopy (PLM) fluorescent confocal imaging map out dynamics vitrification-thawing procedure. Participants/materials, setting, methods A 114 women gave informed consent their surplus immature be used in this project. Oocytes that completed maturation vitro subjected (Oosight) vitrified using Kitazato/Cryotop open system. PLM-positive/negative fixed at 6 steps protocol 2 hours after (15 each subgroup). Microtubules DNA fluorescently labeled inspect chromosome-spindle configuration. Main results role chance Time-course experiments showed PLM-detectable bipolar remained intact all one oocyte (44/45) pre-vitrification equilibration. Notably, PLM signal became more prominent adding cryoprotectant displaced intracellular water. In contrast, progressively disappeared thawing. Specific tubulin labeling revealed microtubule mass was still present most (41/45) from sample group. However, apparatus tended lose its bipolarity disintegrate (8/45) washing steps. This trend accented group lacked spindles before freezing. Here, minority cells (11/45) undergoing rehydration displayed characteristic difference eggś capability ensure apparent even when 13/15 initially PLM-positive 7/15 PLM-negative exhibited normal-shaped spindles. Based these data, we hypothesize transient disappearance warming may attributed restoration destabilization. speed efficiency reconstruction seem depend overall egǵs fitness. Limitations, reasons caution research limited number hormonally-primed extruded polar body shortly retrieval. obtained data represent snapshots process. technically challenging live needed complement description post-vitrification recovery. Wider implications findings Our demonstrate frozen-thawed eggs are not products de novo assembly built preexisting mass. Suboptimal handling reducing interval between ICSI enhance unavoidable compromise developmental potential eggs. Trial registration not-applicable