Essential IVF pp 377-421 | Cite as

The Enigma of Fragmentation in Early Human Embryos: Possible Causes and Clinical Relevance

  • Jonathan Van Blerkom


Blastomere fragmentation is one of the most enigmatic aspects of early human embryogenesis. Within cohorts of embryos maintained under identical conditions, including those cultured in the same dish, fragmentation affects none, some or all embryos during the early cleavage stages. The importance of fragmentation in clinical IVF is related to several questions: First, is this phenomenon indicative of reduced competence or a premorbid condition that argues against transfer to the patient or cryopreservation for future attempts at pregnancy? Second, is fragmentation a normal process in early human development or an in vitro artifact, perhaps associated with suboptimal culture media and conditions, which have yet to be identified? Three, what is the cellular or molecular basis of fragmentation, and do different patterns and extents of fragmentation have a common or different etiology. Virtually all empirically based systems currently used to assess performance in vitro and select human embryos for transfer include some form of fragmentation characterization. For some schemes, the degree of fragmentation is a subjective estimate based on the relative size of the fragment population observed by light microscopy (slight-to- extensive, e.g. Puissant et al, 1987; Giorgetto et al, 1995; Hoover et al, 1995). Depending upon protocols used in clinical IVF laboratories, numerical (e.g., 1-to-4) or letter grades (e.g., A-to-D) may be assigned to represent the apparent degree of fragmentation, which is often determined at a single inspection during cleavage.


Human Embryo Polar Body Cleavage Stage Human Oocyte Developmental Competence 
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© Springer Science+Business Media New York 2004

Authors and Affiliations

  • Jonathan Van Blerkom
    • 1
    • 2
  1. 1.Department of Molecular, Cellular and Developmental BiologyUniversity of ColoradoBoulderUSA
  2. 2.Colorado Reproductive EndocrinologyRose Medical CenterDenverUSA

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