title: Single Day 2 embryo versus blastocyst-stage transfer: a prospective study integrating fresh and frozen embryo transfers.
abstract: BACKGROUND
  Whether extended culture allowing selection of embryos with high development potential has any advantage over cleavage-stage embryo transfer remains a matter of debate. Among the currently unsolved questions, the cumulative delivery rate resulting from fresh and frozen embryo transfers needs to be taken into account in both strategies. The aim of our study was, therefore, to compare the efficacy of single embryo transfer either on Day 2 or on Day 5/6 combining fresh and frozen embryo transfers.
  
  
  METHODS
  A prospective study including 478 couples assigned on a voluntary basis to undergo elective single embryo transfer (eSET, n = 243) on Day 2 or single blastocyst transfer (SBT, n = 235) on Day 5/6 was performed. The primary outcome measurement was the cumulative delivery rate including fresh and frozen-thawed cycles in both groups.
  
  
  RESULTS
  The delivery rate per cycle following fresh embryo transfer was significantly higher in the SBT group compared with the eSET group (P < 0.01). Conversely, frozen embryo and/or blastocyst transfers tended to result in a higher number of deliveries in the eSET compared with the SBT group. Altogether, the cumulative delivery rate per couple, including fresh and frozen embryo transfers, was similar between the two groups (37.9% versus 34.2% in the SBT and eSET groups, respectively).
  
  
  CONCLUSIONS
  The observed cumulative delivery rates in this study do not allow us to take a position in favor of SBT or eSET. An improvement in blastocyst cryopreservation may change this attitude.
authors.affiliation: Service de Médecine et Biologie de la Reproduction, CHRU Bretonneau, 2 Boulevard Tonnelle, 37000 Tours, France.
authors.forename: F
authors.initials: F
authors.lastname: Guerif
authors.forename: M
authors.initials: M
authors.lastname: Lemseffer
authors.forename: R
authors.initials: R
authors.lastname: Bidault
authors.forename: O
authors.initials: O
authors.lastname: Gasnier
authors.forename: M H
authors.initials: MH
authors.lastname: Saussereau
authors.forename: V
authors.initials: V
authors.lastname: Cadoret
authors.forename: C
authors.initials: C
authors.lastname: Jamet
authors.forename: D
authors.initials: D
authors.lastname: Royere
mesh_terms: D000328:Adult; D001755:Blastocyst / Q000166:cytology / Q000502:physiology; D015925:Cryopreservation; D046149:Embryo Culture Techniques; D004624:Embryo Transfer / Q000379:methods*; D004622:Embryo, Mammalian / Q000166:cytology* / Q000502:physiology; D005260:Female; D005307:Fertilization in Vitro; D006801:Humans; D008297:Male; D011247:Pregnancy; D011256:Pregnancy Outcome; D018873:Pregnancy Rate