title: Study of nucleation status in the second cell cycle of human embryo and its impact on implantation rate.
abstract: OBJECTIVE
  To study nucleation status in two- and four-cell embryos and its effect on reproductive outcomes.
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  University-affiliated private center.
  
  
  METHODS
  A total of 1,679 embryos from 940 oocyte donation cycles from May 2012 to May 2014.
  
  
  METHODS
  None.
  
  
  METHODS
  Implantation, morphokinetics, and nucleation status restoration.
  
  
  RESULTS
  Multinucleation was present in 42.53% of embryos with known implantation data at the two-cell stage; it was present in approximately 14% of them at the four-cell stage. In all, 73.4% of the embryos were multinucleated at two cells and restored their nucleation status when they cleaved into four cells. Embryos with blastomeres multinucleated (more than two nuclei) at the four-cell stage showed a lower implantation rate. The average length of S-phase in the first embryo cell cycle in the positive known implantation data (KID+) embryos was longer than in KID- (15.50 hours vs. 14.38 hours) and slightly shorter in the second embryo cell cycle (8.35 hours in KID+ vs. 8.60 hours in KID-).
  
  
  CONCLUSIONS
  Multinucleation in two-cell-stage embryos is a frequent event, which is reversible in a high proportion of embryos, without impact on the implantation rate; and embryos with multinucleated blastomeres have a reduced outcome compared with those with binucleated blastomeres when multinucleation is present in four-cell-stage embryos.
authors.affiliation: IVI Vigo, Vigo, Spain. Electronic address: jesus.aguilar@ivi.es.
authors.forename: Jesus
authors.initials: J
authors.lastname: Aguilar
authors.affiliation: Instituto Valenciano de Infertilidad, Universidad de Valencia, Valencia, Spain.
authors.forename: Irene
authors.initials: I
authors.lastname: Rubio
authors.affiliation: IVI Vigo, Vigo, Spain.
authors.forename: Elkin
authors.initials: E
authors.lastname: Muñoz
authors.affiliation: Instituto Valenciano de Infertilidad, Universidad de Valencia, Valencia, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Pellicer
authors.affiliation: Instituto Valenciano de Infertilidad, Universidad de Valencia, Valencia, Spain.
authors.forename: Marcos
authors.initials: M
authors.lastname: Meseguer
mesh_terms: D001757:Blastomeres / Q000502:physiology*; D002467:Cell Nucleus / Q000502:physiology*; D046149:Embryo Culture Techniques; D010064:Embryo Implantation; D004624:Embryo Transfer; D004622:Embryo, Mammalian / Q000502:physiology*; D005260:Female; D006801:Humans; D007700:Kinetics; D011247:Pregnancy; D018873:Pregnancy Rate; D012189:Retrospective Studies; D016196:S Phase; D020554:Sperm Injections, Intracytoplasmic; D016896:Treatment Outcome
keywords: Embryo kinetic; multinucleation; reversibility; time lapse