Dynamic Morphology of the Human Ooplasm and Subsequent Embryonic Development Analyzed by Time-Lapse Cinematography

Abstract

It has been reported that oocyte dysmorphisms, such as the appearance of a cytoplasmic vacuole, granularity, and deformed shape, are strongly associated with poor embryonic development. In this study, we analyzed the dynamics of cytoplasmic dysmorphisms of oocytes and zygotes using time-lapse cinematography (TLC) that we had originally developed. Mature oocytes (n=1,601) were classified into two groups: good quality oocytes (GQO), which indicated oocytes without any defects; and poor quality oocytes (PQO), oocytes with one or more defect. Of the 1601 oocytes, 74.1% were GQO and the remaining were PQO, which were evaluated by three senior embryologists. The rate of unfertilized oocytes was significantly lower in PQO. GQO also showed a higher development rate to good quality embryos than PQO. The time required for embryonic development in GQO was significantly less than that in PQO (P<0.01). In the zygotes (n=144), 11.4% showed vacuole-like phenomenon (VLP) in the cytoplasm. The VLP appeared in the peripheral cytoplasm after extrusion of the second polar body and moved synchronously as the mPN and fPN migrated toward the central cytoplasm. The VLP size gradually increased and remained after the first cleavage. The rate of multinucleated blastomere (MNB) formation was significantly higher in embryos with VLP than in those without VLP. The appearance of VLP was closely associated with aberrant embryonic development, particularly MNB formation. Our results suggest that the dynamic morphology of the cytoplasm in oocytes and zygotes influences subsequent embryonic development and viability, suggesting that the assessment of oocyte morphology could be a useful parameter in the prediction of embryonic development.