The time aspect in storing vitrified blastocysts: its impact on survival rate, implantation potential and babies born.

STUDY QUESTION Does the storage time of vitrified human blastocysts negatively impact their survival, the implantation potential of embryos or the malformation rate of babies born? SUMMARY ANSWER There was no evidence that storage times of up to 6 years after vitrification (VIT) had a negative impact on blastocyst survival, the implantation potential of embryos or the malformation rate of babies born. WHAT IS KNOWN ALREADY Although several thousand children have been born after blastocyst VIT, many aspects of this technique remain to be elucidated. New applications, such as fertility preservation, lead to long storage times of vitrified gametes or embryos but it remains to be determined if these vitrified embryos are stable over time. STUDY DESIGN, SIZE, DURATION A retrospective study including 603 transfers was conducted between January 2009 and April 2012. Blastocysts were vitrified using a closed system. PARTICIPANTS/MATERIALS, SETTING, METHODS All patients underwent the transfer of aseptically vitrified/warmed blastocysts in a cryo-cycle. A total of 1077 blastocysts were transferred. Survival rates (SRs), implantation potential, birth rates and characteristics of the children born were evaluated. MAIN RESULTS AND THE ROLE OF CHANCE We found that the storage of vitrified blastocysts in aseptic conditions neither impaired blastocyst viability (SR after warming during the first year of storage was 83.0% compared with 83.1% after 5-6 years of storage: NS) nor decreased pregnancy rates (clinical pregnancy rate after 1 year of storage was 40.0 versus 38.5% after 6 years: NS). In addition, no increase in the malformation rate over time was observed. LIMITATIONS, REASONS FOR CAUTION Our study only included the transfer of blastocysts which had been vitrified aseptically (i.e. using a closed system). Therefore, our results might not be applicable to 'open' VIT systems. The long-term follow-up of children born will be necessary to confirm our findings. WIDER IMPLICATIONS OF THE FINDINGS The results suggest that vitrified human blastocysts can be stored for long periods of time without significant negative consequences for the offspring. Therefore, the method should be of benefit to those patients who need to consider taking measures for fertility preservation. STUDY FUNDING/COMPETING INTEREST(S) No external funding was sought for this study and the authors have no conflict of interest to declare.