Effect of equilibration time on clinical and neonatal outcomes in human blastocysts vitrification

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PURPOSE: Prolonged exposure to equilibration solutions may be detrimental to an embryo's developmental potential, whereas a shorter exposure may affect the penetration of cryoprotectants into blastomeres. The purpose of this study was to evaluate the effects of different equilibration times on the clinical and neonatal outcomes of human blastocyst vitrification. METHODS: This is a retrospective study based on data collected between November 2008 and November 2015. A total of 192 blastocysts (80 non-expanded and 112 expanded) obtained from 167 patients were analyzed. The blastocysts were divided into two groups according to their equilibration time: 8-11 minutes or 12-15 minutes. The clinical and neonatal outcomes of warmed blastocysts were evaluated. RESULTS: The survival, implantation, and live birth rates of non-expanded blastocysts were not different between the two groups, but they significantly improved for the expanded blastocysts in the 12-15 minutes group compared to the 8-11 minutes group. The results were similar for the neonatal outcomes after vitrified embryo transfer, when partitioned by equilibration time and blastocyst stage at vitrification. CONCLUSIONS: For the non-expanded blastocysts, a shortened equilibration time (8-11 minutes) is sufficient for effective vitrification.