title: The merits of blastocyst versus cleavage stage embryo transfer: a Cochrane review.
abstract: This paper is based on a Cochrane review published in The Cochrane Library, issue 2, 2002 (see www.CochraneLibrary.net for information) with permission from The Cochrane Collaboration and John Wiley and Sons. Cochrane reviews are regularly updated as new evidence emerges and in response to comments and criticisms, and The Cochrane Library should be consulted for the most recent version of the review.
  
  
  BACKGROUND
  The aim of this study was to determine the relative merits of blastocyst versus cleavage stage embryo transfer, concerning the chance of pregnancy, live birth, multiple pregnancy and the factors contributing to these primary outcomes, from the best available evidence.
  
  
  METHODS
  A systematic review employing the principles of the Cochrane Menstrual Disorders and Subfertility Group was undertaken. Fourteen randomized controlled trials, all comparing day 2/3 with day 5/6 embryo transfer, were included in a meta-analysis.
  
  
  RESULTS
  For day 2/3 versus day 5/6 transfer, there was no significant difference in the odds of pregnancy [odds ratio (OR) = 0.91, 95% confidence interval (CI) 0.71-1.17] nor of live birth (OR = 0.83, 95% CI 0.48-1.42) per treated couple. These results were similar whether all trials, only trials with transfer of equal numbers of day 2/3 versus day 5/6, or only trials with transfer of fewer day 5/6 than day 2/3 embryos, were pooled. There was no significant difference in the odds of multiple pregnancy for day 2/3 versus day 5/6 transfer overall (OR 0.77, 95% CI 0.52-1.13) nor when fewer day 5/6 than day 2/3 embryos were transferred (day 2/3 versus day 5/6 OR 0.69, 95% CI 0.42-1.12).
  
  
  CONCLUSIONS
  The current evidence fails to support a widespread change of practice from cleavage stage to blastocyst stage embryo transfer in couples undergoing IVF.
authors.affiliation: Cochrane Menstrual Disorders & Subfertility Group Editorial Base, Obstetrics & Gynaecology Department, National Women's Hospital, Auckland, New Zealand. debbie.blake@aut.ac.nz
authors.forename: D A
authors.initials: DA
authors.lastname: Blake
authors.forename: M
authors.initials: M
authors.lastname: Proctor
authors.forename: N P
authors.initials: NP
authors.lastname: Johnson
mesh_terms: D001755:Blastocyst; D002970:Cleavage Stage, Ovum; D004624:Embryo Transfer / Q000592:standards*; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D016032:Randomized Controlled Trials as Topic