title: Blastocyst embryo transfer is the primary determinant for improved outcomes in oocyte donation cycles.
abstract: OBJECTIVE
  Using oocyte donation cycles as an ideal model, we sought to compare pregnancy and implantation rates in cleavage stage (day 3) versus blastocyst stage (day 6) embryo transfers (ET); assess the predictive value of blastocyst formation rates based on cleavage cell stage and morphology grade; and evaluate the ability to predict formation of high quality (HQ) blastocysts.
  
  
  METHODS
  Ninety three consecutive oocyte donation cycles from July 2003 to August 2005 were retrospectively evaluated and analyzed to determine if either resulted in a cleavage stage (n = 30) or blastocyst (n = 45) ET. The primary outcomes measured pregnancy rates, the percent development of HQ blastocysts based on day 3 embryo status, and the ability to select day 3 embryos suitable for transfer among four blinded evaluators by assessing their day 6 embryo outcome.
  
  
  RESULTS
  Cleavage stage ET resulted in significantly lower pregnancy rates, clinical pregnancy rates, and implantation rates (47% [n = 14/30]; 40% [n = 12/30] and 27 + or - 7%) compared to blastocyst stage (82% [n = 37/45]; 73% [n = 33/45] and 64 + or - 6% [+ or -SE], P < 0.01). In total, HQ blastocysts resulted from high and good quality day 3 embryos 35% (191/546) and 17% (93/546), respectively. Blinded evaluation revealed at least one, two or all three day 3 embryos were correctly selected for ET on day 6, 97%, 67% and 19%, respectively.
  
  
  CONCLUSIONS
  Day 6 ET resulted in significantly better clinical outcomes compared to day 3 ET. While day 3 status is not predictive of blastocyst quality, the selection of at least one day 3 embryo ultimately suitable for blastocyst ET underscores the significance of optimal endometrial receptivity.
authors.affiliation: Sackler School of Medicine, University of Tel Aviv, Tel Aviv, Israel.
authors.forename: Natalie
authors.initials: N
authors.lastname: Porat
authors.forename: Lynn M
authors.initials: LM
authors.lastname: Boehnlein
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Barker
authors.forename: Peter
authors.initials: P
authors.lastname: Kovacs
authors.forename: Steven R
authors.initials: SR
authors.lastname: Lindheim
mesh_terms: D000328:Adult; D001755:Blastocyst; D016009:Chi-Square Distribution; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods; D006801:Humans; D008875:Middle Aged; D018587:Oocyte Donation / Q000379:methods*; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies; D016896:Treatment Outcome