The influence of intrinsic and extrinsic factors on the developmental potential and chromosomal normality of the human oocyte.

The relationship between factors external to the human oocyte and the developmental potential of the female gamete after meiotic maturation in vivo is discussed. The findings indicate very different intrafollicular oxygen contents exist among follicles from the same and different patients, and marginally hypoxic conditions in some follicles are associated with a comparatively low adenosine triphosphate content and a reduction in intracellular pH for the corresponding metaphase II-stage oocyte. For such oocytes, the finding of an increased frequency of cytoplasmic pathology and chromosomal scattering (aneuploidy) suggests a compromised developmental potential. Three distinctly different patterns of cumulus cell attachment and proliferation during the first 24 hours of culture after insemination are described. As reported earlier, different cumulus cell phenotypes observed in vitro are independent of the presence of the oocyte or fertilized egg and unrelated to the degree of expansion of the cumulus at retrieval. However, developmental viability and implantation potential after in vitro fertilization-embryo transfer appear to be related to an intrinsic pattern of cumulus cell behavior in vitro. The results are discussed with respect to the role of factors external to the human oocyte that may influence or determine the ability of the oocyte to develop progressively after fertilization.