title: Live birth rates after transfer of equal number of blastocysts or cleavage-stage embryos in IVF. A systematic review and meta-analysis.
abstract: BACKGROUND
  Both cleavage-stage and blastocyst-stage embryo transfer policies have advantages and drawbacks. The number of embryos transferred, however, is a crucial parameter that needs to be considered before attempting any comparison.
  
  
  METHODS
  An extensive literature search yielded initially 282 studies from which 8 randomized controlled trials met the inclusion criteria: (i) truly randomized design (ii) policy to transfer equal number of embryos in both the cleavage-stage and the blastocyst-stage groups and (iii) published as full text in a peer-review journal. Primary outcome was the live birth rate and secondary outcomes were clinical pregnancy rate, multiple pregnancy rate, cancellation rate and cryopreservation rate.
  
  
  RESULTS
  A total of 1654 patients were reviewed. Live birth rate per randomized patient was significantly higher (n = 6 studies) in patients who had a blastocyst-stage transfer as compared to patients with cleavage-stage embryo transfer [odds ratio (OR): 1.39, 95% confidence interval (CI): 1.10-1.76; P = 0.005]. Clinical pregnancy rate (OR: 1.27, 95% CI: 1.03-1.55; P = 0.02) and cancellation rate per patient randomized (OR: 2.21, 95% CI: 1.47-3.32; P = 0.0001) were significantly higher in patients with a blastocyst-stage embryo transfer as compared to patients in whom a cleavage-stage embryo transfer was performed. The cryopreservation rate was significantly higher in the cleavage-stage group (OR: 0.28, 95% CI: 0.14-0.55; P = 0.0002).
  
  
  CONCLUSIONS
  The best available evidence suggests that the probability of live birth after fresh IVF is significantly higher after blastocyst-stage embryo transfer as compared to cleavage-stage embryo transfer when equal number of embryos are transferred in the two groups compared.
authors.affiliation: Centre for Reproductive Medicine, University Hospital, Vrije Univestiteit Brussel (Free University of Brussels), Laarbeeklaaan 101, B-1090 Brussels, Belgium. evangelos.papanikolaou@vub.ac.be /
authors.forename: Evangelos G
authors.initials: EG
authors.lastname: Papanikolaou
authors.forename: Efstratios M
authors.initials: EM
authors.lastname: Kolibianakis
authors.forename: Herman
authors.initials: H
authors.lastname: Tournaye
authors.forename: Christos A
authors.initials: CA
authors.lastname: Venetis
authors.forename: Human
authors.initials: H
authors.lastname: Fatemi
authors.forename: Basil
authors.initials: B
authors.lastname: Tarlatzis
authors.forename: Paul
authors.initials: P
authors.lastname: Devroey
mesh_terms: D001723:Birth Rate; D001755:Blastocyst; D002970:Cleavage Stage, Ovum; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D050498:Live Birth; D011247:Pregnancy; D018873:Pregnancy Rate