title: The safety of long-term cryopreservation on slow-frozen early cleavage human embryos.
abstract: OBJECTIVE
  To evaluate the impact of cryopreservation storage time on cleavage-stage embryo survival rate, pregnancy rate, implantation rate, singleton birth weight, and live birth rate.
  
  
  METHODS
  This study was a retrospective analysis, including 867 thaw cycles and 3,367 embryos. Women who underwent IVF-FET cycles between 2005 and 2012 were analyzed. The patients were divided into four groups, as follows: group 1 (12-23 months); group 2 (24-35 months); group 3 (36-48 months); and group 4 (≥48 months).
  
  
  RESULTS
  The storage time did not have a significant effect on survival, damage rate of the blastomeres, implantation rate, pregnancy rate, singleton birth weight, and live birth rate for embryos frozen at cleavage stages.
  
  
  CONCLUSIONS
  Storage time did not influence the survival and pregnancy outcomes of slow-frozen early cleavage human embryos. The developmental potential of cryopreserved human embryos with different storage times does not appear to have a negative influence on further development.
authors.affiliation: Reproductive Medical Centre, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing, China.
authors.forename: Qinli
authors.initials: Q
authors.lastname: Liu
authors.forename: Ying
authors.initials: Y
authors.lastname: Lian
authors.forename: Jin
authors.initials: J
authors.lastname: Huang
authors.forename: Xiulian
authors.initials: X
authors.lastname: Ren
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Shengli
authors.initials: S
authors.lastname: Lin
authors.forename: Ping
authors.initials: P
authors.lastname: Liu
authors.forename: Jie
authors.initials: J
authors.lastname: Qiao
mesh_terms: D000328:Adult; D001724:Birth Weight; D015925:Cryopreservation; D010064:Embryo Implantation; D004624:Embryo Transfer; D047108:Embryonic Development; D005260:Female; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate; D012189:Retrospective Studies; D013997:Time Factors