title: Developmental capacity and pregnancy rate of tetrahedral- versus non-tetrahedral-shaped 4-cell stage human embryos.
abstract: OBJECTIVE
  The arrangement of the blastomeres within the 4-cell stage embryo reflects the orientation of the cleavage planes during the second division. To examine their relevance, the developmental capacity and the pregnancy rate were compared between tetrahedral-shaped and non-tetrahedral-shaped 4-cell stage human embryos.
  
  
  METHODS
  The study included 3,546 4-cell stage embryos. The arrangement of the blastomeres at the 4-cell stage was annotated as being tetrahedral or non-tetrahedral on day 2 of preimplantation development. Embryo quality was compared on day 3 and day 5. Pregnancy rates were calculated per single embryo transfer on day 3 or day 5.
  
  
  RESULTS
  In total, 2,803 4-cell stage embryos (79 %) displayed a tetrahedral arrangement and 743 (21 %) displayed a non-tetrahedral arrangement. Tetrahedral-shaped embryos developed more into high-quality embryos on day 3 (p < 0.001) and day 5 (p = 0.036) and had a higher blastulation rate (p = 0.009). Though, the number of high-quality embryos selected for transfer did not differ between both groups on day 3 (p = 0.167) and day 5 (p ~ 1). Three hundred thirty single embryo transfers were analysed. No significant difference in clinical pregnancy was found between both groups after transfer on day 3 (p = 0.209) and day 5 (p = 0.653).
  
  
  CONCLUSIONS
  The arrangement of the blastomeres according to their previous cleavage planes was correlated to the developmental potential of the 4-cell stage embryo up to the blastocyst stage. If embryo transfers are performed on day 3 and day 5 of development using embryos of adequate quality, the blastomere arrangement at the 4-cell stage had no predictable value regarding pregnancy success.
authors: Centre for Reproductive Medicine, Universitair Ziekenhuis Brussel, Laarbeeklaan 101, 1090, Brussels, Belgium, greet.cauffman@uzbrussel.be.
authors: G
authors: G
authors: Cauffman
authors: G
authors: G
authors: Verheyen
authors: H
authors: H
authors: Tournaye
authors: H
authors: H
authors: Van de Velde
mesh_terms: D000328:Adult; D001757:Blastomeres / Q000166:cytology / Q000648:ultrastructure; D048430:Cell Shape; D004622:Embryo, Mammalian / Q000166:cytology*; D047108:Embryonic Development; D005260:Female; D006801:Humans; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies