Intracytoplasmic morphological abnormalities in human oocytes

In human oocytes, many types of abnormal phenotypes have been observed both within the cytoplasm and outside of the cytoplasm. The morphological evaluation of oocytes and its impact on embryo quality has been controversial. However, abnormal oocyte phenotypes can be directly influenced by the follicular environment, ovarian function and the effects of ovarian stimulation used in assisted reproductive technology. This review focuses on four critical intracytoplasmic anomalies; fluid-filled vacuoles, smooth endoplasmic reticulum clusters (sERC), refractile bodies / lipofuscin bodies and centrally located cytoplasmic granularity (CLCG). The fine structures, morphological and immunochemical characteristics and the possible mechanism giving rise to each phenotype are discussed.