title: The time aspect in storing vitrified blastocysts: its impact on survival rate, implantation potential and babies born.
abstract: OBJECTIVE
  Does the storage time of vitrified human blastocysts negatively impact their survival, the implantation potential of embryos or the malformation rate of babies born?
  
  
  CONCLUSIONS
  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.
  
  
  BACKGROUND
  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.
  
  
  METHODS
  A retrospective study including 603 transfers was conducted between January 2009 and April 2012. Blastocysts were vitrified using a closed system.
  
  
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
  
  
  CONCLUSIONS
  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.
  
  
  BACKGROUND
  No external funding was sought for this study and the authors have no conflict of interest to declare.
authors.affiliation: IVF Centers Prof. Zech - Bregenz, Römerstrasse 2, 6900 Bregenz, Austria.
authors.forename: B
authors.initials: B
authors.lastname: Wirleitner
authors.forename: P
authors.initials: P
authors.lastname: Vanderzwalmen
authors.forename: M
authors.initials: M
authors.lastname: Bach
authors.forename: B
authors.initials: B
authors.lastname: Baramsai
authors.forename: A
authors.initials: A
authors.lastname: Neyer
authors.forename: D
authors.initials: D
authors.lastname: Schwerda
authors.forename: M
authors.initials: M
authors.lastname: Schuff
authors.forename: D
authors.initials: D
authors.lastname: Spitzer
authors.forename: A
authors.initials: A
authors.lastname: Stecher
authors.forename: M
authors.initials: M
authors.lastname: Zintz
authors.forename: N H
authors.initials: NH
authors.lastname: Zech
mesh_terms: D001755:Blastocyst / Q000502:physiology*; D015925:Cryopreservation / Q000379:methods; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer; D005260:Female; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D012189:Retrospective Studies; D013997:Time Factors
keywords: aseptic vitrification; blastocyst; live birth rate; malformation rate; period of storage