Are cumulus cells necessary for the spontaneous maturation of germinal vesicle-stage oocytes to metaphase II

Purpose In this study we investigated the need of the support from cumulus cells for germinal-vesicle (GV) oocytes collected from stimulated ovaries to complete their maturation to metaphase II (MII). Methods: We compared the maturation rate of GV oocytes after coculture with cumulus cells (study group) with their spontaneous maturation in culture medium alone (control group). Results: Sixty-four and nine-tenths percent of the GV oocytes matured to metaphase II in the coculture group, and of these, 43.5% gave normal 2pn zygotes following intracytoplasmic sperm injection (ICSI), while 73.8% of the GV oocytes spontaneously matured to the MII stage and 30% of these reached the zygote stage after ICSI. Conclusions: It is probable that a follicular factor is responsible for this arrested maturation in the human and that maturation occurs spontaneously when the oocytes are separated from their follicular fluid environment after collection.