Vacuolated and post-mature oocyte characteristics: does it matter in fertilization rate and embryo quality?

Oocyte quality is a critical factor in female fertility, and the evaluation of the competent developmental potential of oocytes is one approach to predicting successful fertilization and embryo development. Cytoplasmic vacuoles, perivitelline space (PVS) granularity and size, and fragmented first polar body (PB) are common oocyte abnormalities. The objective of this study is to evaluate the fertilization rate and embryo quality derived from oocytes with vacuolated cytoplasm, as well as oocytes with granulated PVS and fragmented PB. This study examined data from 1051 metaphase II oocytes obtained from 181 women experiencing tubal factor infertility. The oocytes were categorized based on their morphology into three distinct groups: Group N: normal morphology oocyte; Group Vacuole+: oocyte with vacuole-positive cytoplasm; and Group ECAs: oocytes with extracytoplasmic abnormalities (including granulated PVS, large PVS, and fragmented 1st polar body). The subsequent examination of fertilization rate and quality of embryos was conducted following sperm injection. The results showed that the fertilization rate was higher in the group of normal oocytes (Normal) compared to the two other abnormal groups (p < 0.0001). Furthermore, the number of total embryos in the normal morphology group was significantly higher than in the Vacuole + and ECAs groups (p = 0.001). However, the number of low-quality embryos in the Vacuole + group was significantly higher than in the normal oocytes and ECAs groups (p = 0.045). Conversely, the rate of high-quality embryos in the normal group was significantly higher than in the Vacuole + and ECAs groups (p = 0.0001). Oocyte morphology exerts a substantial influence on fertilization rate and embryo quality. However, there is a paucity of consensus regarding the oocyte abnormalities that are more deleterious. These findings suggest that a combination of oocyte abnormalities, including granular PVS, large PVS, fragmented polar bodies, and vacuolated cytoplasm, can have a detrimental effect on fertilization rate and embryo quality.