title: Trophectoderm morphology: an important parameter for predicting live birth after single blastocyst transfer.
abstract: BACKGROUND
  In order to select the best blastocyst for transfer, in humans, three morphological parameters have routinely been used, i.e. degree of blastocoele expansion and appearance of both the trophectoderm (TE) and the inner cell mass (ICM). Although it has been shown that blastocysts with highest scores for all three parameters achieve highest implantation rates, their independent ability to predict pregnancy outcome remains unclear.
  
  
  METHODS
  This study is a retrospective analysis of 1117 fresh day 5 single blastocyst transfers and their live birth outcome related to each morphological parameter.
  
  
  RESULTS
  All three parameters had a significant effect on live birth however, once adjusted for known significant confounders, it was shown that TE was the only statistically significant independent predictor of live birth outcome.
  
  
  CONCLUSIONS
  This study has shown, for the first time, the predictive strength of TE grade over ICM for selecting the best blastocyst for embryo replacement. It may be that, even though ICM is important, a strong TE layer is essential at this stage of embryo development, allowing successful hatching and implantation.
authors.affiliation: Fertility Centre Scandinavia, Carlanderska Hospital, PO Box 5418, S-402 29 Göteborg, Sweden. aish.ahlstrom@fcivf.com
authors.forename: A
authors.initials: A
authors.lastname: Ahlström
authors.forename: C
authors.initials: C
authors.lastname: Westin
authors.forename: E
authors.initials: E
authors.lastname: Reismer
authors.forename: M
authors.initials: M
authors.lastname: Wikland
authors.forename: T
authors.initials: T
authors.lastname: Hardarson
mesh_terms: D000328:Adult; D001755:Blastocyst / Q000166:cytology*; D005260:Female; D006801:Humans; D050498:Live Birth; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011247:Pregnancy; D011336:Probability; D012189:Retrospective Studies; D056826:Single Embryo Transfer