title: Blastocyst transfer in frozen-thawed cycles.
abstract: OBJECTIVE
  It is well known that fresh blastocyst transfer results in better pregnancy outcomes with a smaller number of transferred embryos compared with cleavage stage embryo transfer. However, in terms of frozen-thawed blastocyst transfer, only a few studies are available. We aimed to evaluate clinical outcomes of frozen-thawed embryo transfer (FET) with blastocysts.
  
  
  METHODS
  Retrospective analysis of FET cycles with blastocysts (B-FET) between Jan 2007 and June 2009 was performed. Age-matched FET cycles with cleavage stage embryos (C-FET) during the same period were collected as controls. A total of 58 B-FET cycles were compared with 172 C-FET cycles and also compared with those of post-thaw extended culture blastocysts from frozen pronuclear stage embryos (22 cycles).
  
  
  RESULTS
  There was no difference in the patient characteristics of each group. The embryos' survival rates after thawing were comparable (>90%) and there was no difference in the implantation rate or clinical and ongoing pregnancy rate among the three groups.
  
  
  CONCLUSIONS
  In FET, blastocyst transfers may not present better pregnancy outcomes than cleavage stage embryo transfers. A further large-scale prospective study is needed.
authors.affiliation: Department of Obstetrics and Gynecology, Kyungpook National University Hospital, Daegu, Korea.
authors.forename: Ae Ra
authors.initials: AR
authors.lastname: Han
authors.forename: Chan Woo
authors.initials: CW
authors.lastname: Park
authors.forename: Hyoung-Song
authors.initials: HS
authors.lastname: Lee
authors.forename: Kwang Moon
authors.initials: KM
authors.lastname: Yang
authors.forename: In Ok
authors.initials: IO
authors.lastname: Song
authors.forename: Mi Kyoung
authors.initials: MK
authors.lastname: Koong
keywords: Blastocyst; Frozen-thawed embryo transfer; Pregnancy outcome