Does the number of embryos loaded on a single cryo-carrier affect post-vitrification survival rate?

Adva Aizer*, Meirav Noach-Hirsh, Olga Dratviman-Storobinsky, Jigal Haas, Raoul Orvieto

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Background: We aimed to assess whether the survival rate of embryos is influenced by the number of embryos/oocytes loaded on a single cryo-carrier during vitrification. Methods: This was a retrospective study that included 974 patients who underwent thawing of 1896 embryo-warming cycles between September 2016 and January 2020. A distinct analysis was made for cleavage stage embryos (2-10-cell stage) and blastocysts. For vitrification, embryos were placed in a Cryotop™ open device using a SAGE vitrification kit following the manufacturer's instructions. Warming was carried using a SAGE warming vitrification kit according the manufacturer's instructions. Results: Total post-vitrification survival rates of embryos at the cleavage stage or blastocyst stage was 94.8%. At the cleavage stage, cryo-preserving three embryos per single cryo-carrier gave the highest full intact embryo survival rate (91.5%) compared with one or two embryo(s) per single cryo-carrier (85.7%, P < 0.0002 and 87.3%, P < 0.004). Conversely, post warmed full intact blastocyst survival rate for two blastocysts was significantly lower compared with one blastocyst (76.7% vs. 87.9%, P < 0.0193) per single cryo-carrier. Conclusion: Post-thawing survival rate following vitrification is affected by the number of embryos per single cryo-carrier undergoing the vitrification equilibration phase, with the optimum number of three cleaved embryos or one blastocyst per single cryo-carrier. Further studies are required to determine the optimum number of cleaved embryos or blastocysts that should be loaded onto a single cryo-carrier vitrification device.

Original languageEnglish
Pages (from-to)87-91
Issue number1
StatePublished - 2021


  • Cryo-carrier
  • Cryopreservation
  • Cryotop
  • Straw
  • Survival rate
  • Vitrification


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