title: A prospective randomized study: day 2 versus day 5 embryo transfer.
abstract: BACKGROUND
  This randomized controlled study was performed in an unselected IVF/ICSI population to test the hypothesis that blastocyst transfers result in higher clinical pregnancy rates (CPR) per oocyte retrieval when compared with day 2 transfers.
  
  
  METHODS
  Blind randomization for transfer on day 2 (group 1) or day 5/6 (group 2) was performed before stimulation. Oocytes and embryos were cultured in sequential media in 5.5% CO(2), 5% O(2), 89.5% N(2) and 90% humidity. A maximum of two embryos was transferred.
  
  
  RESULTS
  The two groups were similar for age, IVF indication, number of treatment cycles, rate of ICSI/IVF, number of fertilized oocytes and number of embryos transferred. The CPR/oocyte retrieval was comparable in group 1 (32%) and in group 2 (44%), while the CPR/embryo transfer was significantly higher (P < 0.01) in group 2 (60%) than in group 1 (35%). Similarly, the implantation rate per embryo transferred was significantly higher (P < 0.03) in group 2 (46%) than in group 1 (29%). The cryo-augmented delivery rate/oocyte retrieval was comparable in group 2 (36.3%) and in group 1 (28.6%).
  
  
  CONCLUSIONS
  This randomized study in an unselected population showed a significantly higher CPR/embryo transfer and a tendency toward a higher CPR/oocyte retrieval in patients receiving blastocysts when compared with day 2 transfers.
authors.affiliation: Leuven University Fertility Center, University Hospital Gasthuisberg, Catholic University Leuven, Herestraat 49, B-3000 Leuven, Belgium. Ingrid.Vanderauwera@pandora.be
authors.forename: Ingrid
authors.initials: I
authors.lastname: Van der Auwera
authors.forename: Sophie
authors.initials: S
authors.lastname: Debrock
authors.forename: Carl
authors.initials: C
authors.lastname: Spiessens
authors.forename: Hilde
authors.initials: H
authors.lastname: Afschrift
authors.forename: Els
authors.initials: E
authors.lastname: Bakelants
authors.forename: Christel
authors.initials: C
authors.lastname: Meuleman
authors.forename: Luc
authors.initials: L
authors.lastname: Meeuwis
authors.forename: Thomas M
authors.initials: TM
authors.lastname: D'Hooghe
mesh_terms: D000328:Adult; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D011247:Pregnancy; D011446:Prospective Studies; D020554:Sperm Injections, Intracytoplasmic; D013997:Time Factors