title: Can cumulative pregnancy rates be increased by freezing and thawing single embryos?
abstract: OBJECTIVE
  To evaluate the extent to which transfers of frozen single embryos increase cumulative pregnancy rates.
  
  
  METHODS
  Retrospective analysis.
  
  
  METHODS
  IVF unit of a university hospital.
  
  
  METHODS
  Patients undergoing IVF cycles that were carried out from 2001 to 2005 (n = 1758). Patients were assigned to three groups according to the number of embryos frozen: group A, no cryopreservation; group B, a single embryo frozen; group C, several embryos frozen.
  
  
  METHODS
  Analysis of fresh ETs as a function of the number of embryos frozen and comparison outcomes for the thawing of a single embryo between subgroups B* (only one embryo frozen and thawed) and C* (last embryo of the cohort thawed).
  
  
  METHODS
  Implantation and pregnancy rates after fresh ETs and embryo survival and pregnancy rates after the transfer of a single thawed embryo.
  
  
  RESULTS
  The pregnancy rate per fresh ET increased significantly with the number of embryos frozen: 16.2% in group A, 21.4% in group B, and 26.5% in group C. For single thawed embryos, survival was higher in group C* (91.7%) than in group B* (72.6%). The pregnancy rate was also significantly higher in group C* (19.4% vs. 0%).
  
  
  CONCLUSIONS
  The freezing of single embryos is of no benefit in cumulative pregnancy rates. ET strategies should therefore be reviewed.
authors.affiliation: Reproductive Biology Unit, University Hospital, Hôpital Pitié-Salpêtrière, Paris, France. marie.prades@psl.aphp.fr
authors.forename: Marie
authors.initials: M
authors.lastname: Prades
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Golmard
authors.forename: Danièle
authors.initials: D
authors.lastname: Vauthier
authors.forename: Gilles
authors.initials: G
authors.lastname: Lefèbvre
authors.forename: Catherine
authors.initials: C
authors.lastname: Poirot
mesh_terms: D000328:Adult; D015925:Cryopreservation; D010064:Embryo Implantation; D004624:Embryo Transfer; D004622:Embryo, Mammalian; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies; D016896:Treatment Outcome