The aim of this study was to evaluate the impact of different cryopreservation protocols on the repolymerization of metaphase (M)II spindles in human oocytes. Fresh aspirated donor oocytes were cryopreserved 3-4 h after retrieval using four different protocols: slow freezing using 1.5 mol/l 1,2-propanediol (PROH) + 0.2 mol/l sucrose (n = 36); 1.5 mol/l PROH + 0.3 mol/l sucrose (n = 34); 1.5 mol/l PROH + 0.3 mol/l sucrose with Na(+) depleted-choline replaced media (n = 27), and vitrification by the Cryotip method (n = 23). The control group comprised 34 fresh oocytes. Three hours after thawing, surviving and control oocytes were fixed for meiotic spindle/chromatin assessment. Survival rates were 63.8, 73.5, 74.1 and 86.9% respectively for the four protocols described above. Survival for vitrified oocytes was higher than that observed for slow freezing with 0.2 and 0.3 mol/l sucrose (P < 0.05). The proportion of oocytes showing normal spindle configuration was similar for the four protocols (81, 73.9, 88.9 and 81.3% respectively) and 88.5% for controls, showing that the MII spindle returns to its normal configuration after 3 h of post-thawing incubation under standard conditions, irrespective of the cryopreservation technique used.

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