title: Vitrification versus slow freezing gives excellent survival, post warming embryo morphology and pregnancy outcomes for human cleaved embryos.
abstract: OBJECTIVE
  The objective of this retrospective study was to evaluate the efficacy of vitrification and slow freezing for the cryopreservation of human cleavage stage embryos in terms of post-warming survival rate, post-warming embryo morphology and clinical outcomes.
  
  
  METHODS
  The embryos of 305 patients at cleavage stages were cryopreserved either with vitrification (153 patients) or slow-freezing (152 patients) methods. After warming; the survival rate, post-warmed embryo morphology, clinical pregnancy and implantation rates were evaluated and compared between the two groups.
  
  
  RESULTS
  In the vitrification group versus slow freezing group, the survival rate (96.9% vs. 82.8%) and the post-warmed excellent morphology with all blastomeres intact (91.8% vs. 56.2%) were higher with an odds ratio of 6.607 (95% confidence interval; 4.184-10.434) and 8.769 (95% confidence interval; 6.460-11.904), respectively. In this group, the clinical pregnancy rate (40.5% vs. 21.4%) and the implantation rate (16.6% vs. 6.8%) were also higher with an odds ratio of 2.427 (95%confidence interval; 1.461-4.033) and 2.726 (95% confidence interval; 1.837-4.046), respectively.
  
  
  CONCLUSIONS
  Vitrification in contrast to slow freezing is an efficient method for cryopreservation of human cleavage stage embryos. Vitrification provides a higher survival rate, minimal deleterious effects on post-warming embryo morphology and it can improve clinical outcomes.
authors.affiliation: Embryology Department, Reproductive Medicine Research Center, Royan Institute, ACECR, 19395-4644, Tehran, Iran. mr_valojerdi@yahoo.com
authors.forename: Mojtaba
authors.initials: M
authors.lastname: Rezazadeh Valojerdi
authors.forename: Poopak
authors.initials: P
authors.lastname: Eftekhari-Yazdi
authors.forename: Leila
authors.initials: L
authors.lastname: Karimian
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Hassani
authors.forename: Bahar
authors.initials: B
authors.lastname: Movaghar
mesh_terms: D000328:Adult; D015925:Cryopreservation / Q000379:methods*; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer; D004622:Embryo, Mammalian; D005260:Female; D005615:Freezing; D006801:Humans; D010062:Ovulation Induction; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies