title: Better perinatal outcomes following transfer of fresh blastocysts and blastocysts cultured from thawed cleavage embryos: a population-based study.
abstract: BACKGROUND
  Fresh embryo transfer results in higher live birth rates, while thawed embryo transfer appears to result in healthier babies. This study aims to investigate the association between the transfer of fresh or thawed embryos at the cleavage or blastocyst stage and the perinatal outcomes.
  
  
  METHODS
  This analysis is a retrospective population-based study of 150 376 autologous embryo transfer cycles in Australia during 2002-2006. The rates of pregnancy, live delivery and 'healthy baby' delivery (a single baby born live at term, weighing >or=2500 g, surviving for at least 28 days post birth and not having congenital anomalies) were compared after transfer of fresh cleavage embryos, fresh blastocysts, thawed cleavage embryos, blastocysts from thawed cleavage embryos and thawed blastocysts.
  
  
  RESULTS
  The live delivery rate was significantly higher for transfer of fresh blastocysts (27.9%) than for blastocysts cultured from thawed cleavage embryos (22.0%), fresh cleavage embryos (21.7%), thawed blastocysts (16.3%) and thawed cleavage embryos (15.2%). Compared with the transfer of fresh blastocysts, the likelihood of a 'healthy baby' was significantly lower for blastocysts from thawed cleavage embryos [adjusted odds ratios (AOR) 0.73, 95% confidence intervals (CI) 0.65-0.82], fresh cleavage embryos (AOR 0.67, 95% CI 0.64-0.69), thawed blastocysts (AOR 0.57, 95% CI 0.53-0.62) and thawed cleavage embryos (AOR 0.53, 95% CI 0.51-0.56). Of thaw cycles, transfers of thawed blastocysts (AOR 0.79, 95% CI 0.70-0.89) and thawed cleavage embryos (AOR 0.71, 95% CI 0.63-0.79) had significantly lower odds of 'healthy baby' than transfer of blastocysts from thawed cleavage embryos.
  
  
  CONCLUSIONS
  These data suggest that an optimum practice model to maximize the outcomes of the birth of a 'healthy baby' is the transfer of blastocysts and the freezing of cleavage embryos in fresh cycles and subsequent transfer of blastocysts cultured from these thawed cleavage embryos.
authors.affiliation: Perinatal and Reproductive Epidemiology Research Unit, School Women's and Children's Health, University of New South Wales, Level 2, McNevin Dickson Building, Randwick Hospitals Campus, Randwick, NSW 2031, Australia. alex.wang@unsw.edu.au
authors.forename: Yueping Alex
authors.initials: YA
authors.lastname: Wang
authors.forename: Michael
authors.initials: M
authors.lastname: Chapman
authors.forename: Michael
authors.initials: M
authors.lastname: Costello
authors.forename: Elizabeth Anne
authors.initials: EA
authors.lastname: Sullivan
mesh_terms: D001315:Australia; D001755:Blastocyst; D016009:Chi-Square Distribution; D002970:Cleavage Stage, Ovum; D015925:Cryopreservation; D016208:Databases, Factual; D046149:Embryo Culture Techniques; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods*; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies; D016896:Treatment Outcome