title: A comparison of efficacy of freezing embryos at the 2 pronuclear (2PN) stage vs multi-cell when using a simplified freezing protocol with one-step removal of cryoprotectant.
abstract: OBJECTIVE
  To compare the efficacy of freezing embryos at the 2 pronuclear stage vs multi-cell stage using a simplified freezing protocol with a one-step removal of the cryoprotectant.
  
  
  METHODS
  A retrospective analysis was performed. Survival, delivered pregnancy and implantation rates were compared in transfers of all embryos frozen at 2 pronuclear stage (2PN) or all embryos frozen at multi-cell stage. The results were further stratified and compared according to the number of high quality embryos transferred.
  
  
  RESULTS
  In all categories despite comparing similar numbers and quality of embryos transferred there was a significantly higher survival rate of 2PN embryos. Significantly higher delivered pregnancy and implantation rates were seen with 2PN vs multi-cell embryos when there was only one or two embryos with > or = 6 blastomeres and < 25% fragmentation, and a trend for higher delivered pregnancy rates when there were three top quality embryos transferred.
  
  
  CONCLUSIONS
  When given the option it is preferable when using this simplified freezing and thawing protocol to freeze at the 2PN stage.
authors.affiliation: The University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School at Camden, Cooper Hospital/University Medical Center, Department of Obstetrics and Gynecology, Division of Reproductive Endocrinology & Infertility, Camden, NJ, USA. laurie@ccivf.com
authors.forename: J H
authors.initials: JH
authors.lastname: Check
authors.forename: D
authors.initials: D
authors.lastname: Summers-Chase
authors.forename: D
authors.initials: D
authors.lastname: Horwath
authors.forename: K
authors.initials: K
authors.lastname: Swenson
authors.forename: W
authors.initials: W
authors.lastname: Yuan
mesh_terms: D001757:Blastomeres; D015925:Cryopreservation / Q000379:methods*; D004622:Embryo, Mammalian; D005260:Female; D006801:Humans; D011247:Pregnancy; D017388:Zygote Intrafallopian Transfer