title: Pregnancy achieved with pronuclear-stage embryos that were cryopreserved and thawed twice: a case report.
abstract: OBJECTIVE
  Our purpose was to determine if pronuclear-stage embryos (2PN) could be thawed, then frozen again with subsequent survival and cleavage after thawing.
  
  
  METHODS
  A simplified cryopreservation protocol was used in which a slow cooling program is started at the seeding temperature of -6 degrees C in an alcohol-bath controlled-rate freezer. 1,2-Propanediol (1.5 M) was added to embryos before cooling. A fast thawing technique at room temperature was used. The cryoprotectant was removed in one step using a 1 M sucrose solution.
  
  
  RESULTS
  Three months after refreezing, the three 2PN embryos were thawed and all three cleaved after 24 hr in culture. Following embryo transfer a pregnancy was achieved and a healthy full-term baby girl was born.
  
  
  CONCLUSIONS
  This is the third case reported of successful pregnancies after transfer of human embryos that were frozen twice before transfer and the first case where the second freeze occurred at the pronuclear stage. This is also the first successful refreezing of human embryos using a simplified freezing and thawing technique with one-step addition and removal of cryoprotectant.
authors.affiliation: University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School at Camden, USA.
authors.forename: A
authors.initials: A
authors.lastname: Baker
authors.forename: J H
authors.initials: JH
authors.lastname: Check
authors.forename: D
authors.initials: D
authors.lastname: Lurie
authors.forename: C
authors.initials: C
authors.lastname: Hourani
authors.forename: L M
authors.initials: LM
authors.lastname: Hoover
mesh_terms: D000328:Adult; D015925:Cryopreservation; D004624:Embryo Transfer; D004622:Embryo, Mammalian; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D008597:Menstrual Cycle; D011247:Pregnancy; D011256:Pregnancy Outcome