title: Cryopreserved embryo transfers suggest that endometrial receptivity may contribute to reduced success rates of later developing embryos.
abstract: OBJECTIVE
  To evaluate viability and implantation potential of cryopreserved blastocysts according to the day of blastocyst expansion and cryopreservation.
  
  
  METHODS
  Retrospective study.
  
  
  METHODS
  Private ART center.
  
  
  METHODS
  Three hundred and seventy-five patients undergoing embryo transfer with cryopreserved blastocysts.
  
  
  METHODS
  Blastocyst cryopreservation on day 5, 6, or 7 after oocyte retrieval according to the day of blastocyst expansion and subsequent embryo transfer.
  
  
  METHODS
  Clinical pregnancy rate (PR) per embryo transfer.
  
  
  RESULTS
  Clinical PRs were similar between blastocysts cryopreserved on day 5 and blastocysts cryopreserved on day 6 (32% vs. 28%). The clinical PR was lower for blastocysts cryopreserved on day 7 (15%), but this difference was not statistically significant after accounting for the number of embryos per transfer (P=.15).
  
  
  CONCLUSIONS
  Viability and implantation potential are similar for day 5 and day 6 blastocyst cryopreservation. Viability may be reduced for blastocysts cryopreserved on day 7, but not to the extent suggested by reports of fresh transfers. These results suggest that reduced success rates associated with fresh transfers of later developing blastocysts may be the result of asynchrony with endometrial receptivity instead of poorer embryo quality.
authors.affiliation: Shady Grove Fertility Reproductive Science Center, Rockville, Maryland 20850, USA. kevin.richter@integramed.com
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Richter
authors.forename: Sharon K
authors.initials: SK
authors.lastname: Shipley
authors.forename: Ingrid
authors.initials: I
authors.lastname: McVearry
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Tucker
authors.forename: Eric A
authors.initials: EA
authors.lastname: Widra
mesh_terms: D000328:Adult; D015925:Cryopreservation / Q000379:methods*; D004624:Embryo Transfer; D047108:Embryonic Development; D004717:Endometrium / Q000166:cytology*; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies; D020554:Sperm Injections, Intracytoplasmic; D016896:Treatment Outcome