Fine structural markers of human oocyte quality in assisted reproduction.

After completing its maturation, the human oocyte acquires very peculiar fine structural features. In this review we describe by LM, TEM and SEM the nuclear and cytoplasmic changes, as well as the changes in the texture of the ZP, occurring in the human oocyte during the final stages of maturation. Oocytes were obtained during ART cycles and destined to morphological evaluation after the informed consent of the patients. The critical analysis of the data reviewed leads us to emphasize that: 1. both the completion of the maturative changes in the preovulatory period and the absence of degenerative alterations in the cytoplasmic microdomains of the human mature oocyte ultimately render the female gamete competent for fertilization; 2. several minute cellular aberrations, detectable only by electron microscopy analysis, may occur in the human oocyte as the consequence of the application of ART protocols (IVM and cryopreservation, in particular) and could be responsible for ART failures, even affecting early embryo development.