title: Influence of storage time on vitrified human cleavage-stage embryos froze in open system.
abstract: BACKGROUND
  During in vitro fertilization, rapid growth of vitrification and liquid nitrogen storage of embryos have been well characterized. However, the effect of storage time on vitrified cleavage-stage embryos in an open system is poorly understood.
  
  
  OBJECTIVE
  To investigate the influence of storage time on the survival and pregnancy outcomes of vitrified human cleavage-stage embryos froze and stored in an open system.
  
  
  METHODS
  A retrospective study of 786 vitrified-warmed cycles of 735 patients was performed from January 2013 to October 2013. The cycles were divided into five groups according to storage time: 1-3 months, 4-6 months, 7-12 months, 13-24 and 25-60 months. The clinical outcomes of cycles with different storage time were analyzed.
  
  
  RESULTS
  There were no significant differences of the survival rate, clinical pregnancy outcomes, birth rate, gestational weeks and singleton birthweights at various storage times.
  
  
  CONCLUSIONS
  For vitrified embryos froze and stored in an open system, the storage time would not influence the survival rate and pregnancy outcomes by storage time up to 5 years.
authors.affiliation: a The ART Center, Northwest Women's and Children's Hospital , Xi'an , China.
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.affiliation: a The ART Center, Northwest Women's and Children's Hospital , Xi'an , China.
authors.forename: Wanqiu
authors.initials: W
authors.lastname: Zhao
authors.affiliation: a The ART Center, Northwest Women's and Children's Hospital , Xi'an , China.
authors.forename: Xia
authors.initials: X
authors.lastname: Xue
authors.affiliation: a The ART Center, Northwest Women's and Children's Hospital , Xi'an , China.
authors.forename: Silin
authors.initials: S
authors.lastname: Zhang
authors.affiliation: a The ART Center, Northwest Women's and Children's Hospital , Xi'an , China.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: a The ART Center, Northwest Women's and Children's Hospital , Xi'an , China.
authors.forename: Juanzi
authors.initials: J
authors.lastname: Shi
mesh_terms: D000328:Adult; D002970:Cleavage Stage, Ovum / Q000502:physiology*; D015925:Cryopreservation / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D010043:Outcome and Process Assessment, Health Care / Q000706:statistics & numerical data*; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D013997:Time Factors; D058989:Vitrification
keywords: Cleavage-stage embryos; open system; pregnancy outcomes; storage time; survival rate; vitrification