title: Single blastocyst embryo transfer maintains comparable pregnancy rates to double cleavage-stage embryo transfer but results in healthier pregnancy outcomes.
abstract: BACKGROUND
  The optimal outcome after IVF is a live, healthy, singleton term baby. This can be achieved by transferring a single embryo, but at the possible expense of reducing pregnancy rates. Recent studies suggest that delaying transfer of embryos to the blastocyst stage (day 4/5), rather than the more traditional cleavage stage (day 2-3), allows for better selection of the best embryo, maximising pregnancy rates from a single embryo transfer (SET). The aim of this study was to assess pregnancy outcomes in relation to changing embryo transfer practices.
  
  
  METHODS
  A retrospective analysis of pregnancy outcomes was made between IVF cycles conducted in 2007 when blastocyst SET became standard practice, with IVF cycles in 2003 when double cleavage-stage embryo transfer was the norm.
  
  
  RESULTS
  The implementation of a blastocyst SET policy resulted in a significant decrease in multiple birth rates, while maintaining live birth delivery rate comparable to double cleavage-stage transfer (27.2% versus 24.8%, respectively, N.S.).
  
  
  CONCLUSIONS
  Improvements in culturing protocols have facilitated extended culture, increasing embryo selection capability. These results indicate that it is now possible to maintain excellent pregnancy rates with SET blastocyst culture, while decreasing complications related to multiple births.
authors.affiliation: Repromed, Dulwich, South Australia, Australia. dzander@repromed.com.au
authors.forename: Deirdre L
authors.initials: DL
authors.lastname: Zander-Fox
authors.forename: Kelton
authors.initials: K
authors.lastname: Tremellen
authors.forename: Michelle
authors.initials: M
authors.lastname: Lane
mesh_terms: D000328:Adult; D001755:Blastocyst; D002970:Cleavage Stage, Ovum; D004624:Embryo Transfer / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro; D006340:Heart Rate, Fetal; D006801:Humans; D007231:Infant, Newborn; D016014:Linear Models; D050498:Live Birth; D008297:Male; D011247:Pregnancy; D018873:Pregnancy Rate; D011272:Pregnancy, Multiple; D059286:Pregnancy, Triplet / Q000706:statistics & numerical data; D059285:Pregnancy, Twin / Q000706:statistics & numerical data; D047928:Premature Birth / Q000453:epidemiology; D012189:Retrospective Studies; D056826:Single Embryo Transfer