title: Separation of a pronucleus by premature cytokinesis: a mechanism for immediate diploidization of tripronuclear oocytes?
abstract: OBJECTIVE
  To describe an oocyte with a peculiar combination of abnormalities in terms of cytoplasmic fragmentation and formation of pronuclei.
  
  
  METHODS
  Case report.
  
  
  METHODS
  University-based IVF unit.
  
  
  METHODS
  A chromosomally normal couple undergoing the third treatment by assisted reproduction.
  
  
  METHODS
  Controlled ovarian hyperstimulation, follicular aspiration, testicular sperm extraction, intracytoplasmic sperm injection (ICSI), and oocyte fixation.
  
  
  METHODS
  Assessment of pronuclear formation and cytogenetic analysis of a tripronuclear fragmented oocyte.
  
  
  RESULTS
  The described oocyte revealed two polar body-like structures after follicular aspiration and developed three pronuclei after ICSI, accompanied by extrusion of another polar body-like globule. Moreover, the pronuclear stage had undergone a premature irregular cytokinesis, including one of the pronuclei in the smaller half of the divided cytoplasm. Cytogenetic analysis showed a triploid karyotype (23,X/23,X,ace/23,Y) commonly found in digynic ICSI zygotes.
  
  
  CONCLUSIONS
  The chromosomal constitution suggests that the third globule represents another cytoplasmic fragment and no regular second polar body. Separation of a supernumerary pronucleus by premature cytokinesis might be relevant for the discussion on diploidization of triploid zygotes.
authors.affiliation: Department of Gynaecology and Obstetrics, University of Ulm, Prittwitzstrasse 43, Ulm, Germany. bernd.rosenbusch@uniklinik-ulm.de
authors.forename: Bernd E
authors.initials: BE
authors.lastname: Rosenbusch
authors.forename: Michael
authors.initials: M
authors.lastname: Schneider