Meiotic spindle recovery is faster in vitrification of human oocytes compared to slow freezing.

OBJECTIVE: To investigate spindle behavior during and after slow freezing at room temperature (RT) and vitrification at different temperatures. DESIGN: Randomized, comparative study. SETTING: University hospital. PATIENT(S): Patients undergoing IVF treatment volunteered for the study and donated part of their supernumerary oocytes. INTERVENTION(S): Metaphase II oocytes were divided into group A: slow freezing RT /thawing RT; group B: vitrification RT/warming RT; group C: vitrification RT/warming 37 degrees C; and group D: vitrification 37 degrees C/warming 37 degrees C. Spindle presence was evaluated at each step of the four procedures and in culture. MAIN OUTCOME MEASURE(S): Cumulative spindle recovery rate comparing warming phase of the three vitrification groups and culture phase among the four groups. RESULT(S): During warming, the three vitrification groups showed a significantly fast spindle recovery rate compared to the thawing of the slow freezing group. A progressively significant fast cumulative recovery rate was observed in the three vitrification groups by increasing the number of phases at physiological temperature (hazard rate = 2.68; 95% confidence interval 1.71-4.02). CONCLUSION(S): The present study demonstrates that spindle recovery is faster in vitrification than in slow freezing. These data support a possible protective effect of vitrification/warming at 37 degrees C on the meiotic spindle structure and, therefore, on the subsequent clinical outcome of the procedure, although comparative clinical studies are needed.