title: In vitro development and implantation rates of fresh and cryopreserved sibling zygotes.
abstract: OBJECTIVE
  To compare the developmental potential of cryopreserved human zygotes after thawing to sibling zygotes that were transferred without cryopreservation.
  
  
  METHODS
  Retrospective analysis of embryo data and pregnancy outcome for all in vitro fertilization (IVF) patients who had sufficient zygotes to allow fresh embryo transfer and cryopreservation of additional sibling zygotes for later use.
  
  
  RESULTS
  Zygotes survived cryopreservation at a high rate (87%). After thawing, cryopreserved zygotes developed at rates similar to those of fresh zygotes. Pregnancy occurred at similar rates after replacement of fresh embryos (27.9%) or replacement of cryopreserved-thawed zygote-derived embryos (24.3%).
  
  
  CONCLUSIONS
  Human embryos can be cryopreserved at the pronuclear zygote stage with little loss of developmental potential. Cryopreservation allowed a reduction in the number of embryos transferred during an IVF retrieval cycle, thereby reducing the occurrence of multiple pregnancy. The total cumulative pregnancy rate per retrieval cycle doubled when pregnancies from cryopreserved-thawed zygotes were added to those originating from fresh zygotes.
authors.affiliation: Department of Gynecology, Cleveland Clinic Foundation, Ohio, USA.
authors.forename: K F
authors.initials: KF
authors.lastname: Miller
authors.forename: J M
authors.initials: JM
authors.lastname: Goldberg
mesh_terms: D015925:Cryopreservation; D004624:Embryo Transfer / Q000379:methods / Q000706:statistics & numerical data; D005314:Embryonic and Fetal Development; D005260:Female; D006801:Humans; D009679:Nuclear Family; D011247:Pregnancy / Q000706:statistics & numerical data; D012189:Retrospective Studies; D017388:Zygote Intrafallopian Transfer / Q000379:methods / Q000706:statistics & numerical data