Optimal timing of oocyte maturation and its relationship with the spindle assembly and developmental competence of in vitro matured human oocytes

Objective: To develop and test a simple, feasible approach to improve spindle assembly and developmental competence of human in vitro matured oocytes by parthenogenetic activation in maturation medium.

Design: Prospective, randomized study.

Setting: University research laboratory-based assisted reproductive technology laboratory.

Patient(s): Four hundred thirty-two patients with male factor infertility undergoing intracytoplasmic sperm injection (ICSI) cycles.

Intervention(s): In vivo failed-to-mature oocytes from the ICSI cycles were divided into four groups according to differing duration after the extrusion of first polar body (0-1, 2-3, 4-5, and 8-9 hours). Oocytes spindles in each group were immunostained for α-tubulin and chromosomes, and observed by confocal microscopy.

Main outcome measure(s): Rate from pronuclear stage to blastocyst, embryo grading at the eight-cell and blastocyst stages, and spindle assembly.

Result(s): There was a statistically significantly higher rate of development at the eight-cell and blastocyst stages in the 2- to 3-hour and 4- to 5-hour groups. The grading results at the eight-cell and blastocyst stages also showed that the proportion of embryos of high quality was similar among the 2- to 3-hour and 4- to 5-hour groups, and in these groups it was statistically significantly higher than the 0- to 1-hour and 8- to 9-hour groups. The results of immunofluorescence demonstrated that there was a statistically significantly higher rate of normal spindle assembly in the 2- to 3-hour and 4- to 5-hour groups.

Conclusion(s): Optimal timing of maturation benefits the development of competence of in vitro matured oocytes by promoting normal spindle assembly.