Human oocyte maturation in vitro is stimulated by meiosis-activating sterol.

In-vitro studies in mouse oocytes have shown that the C-29 endogenously occurring sterol FF-MAS (follicular fluid meiosis-activating sterol) is a potent inducer of meiotic maturation leading to increased fertilization rates. We have used synthetic FF-MAS to induce meiotic maturation in immature human oocytes aspirated from polycystic ovarian syndrome patients. The patients were asked to give written consent to donate half of their aspirated oocytes to investigate the influence of culture conditions on maturation kinetics. The oocytes were aspirated from follicles 8-12 mm in diameter under ultrasound guidance after initial treatment with a gonadotrophin-releasing hormone agonist and s.c. injections of recombinant FSH for 3 days. The other half of the oocytes remained outside this present study. They were reserved for the patients' benefit and were fertilized with appropriate embryo stages being transferred. Fertilization and transfer were not attempted for the study oocytes. Synthetic sterol FF-MAS was added to the culture media at a concentration of 20 micromol/l and nuclear maturation was compared to a control group of oocytes cultured in media only supplemented with vehicle (TCM-199 supplemented with 0.2% ethanol v/v); thus no additional hormones, growth factors, serum or follicle fluid were added. In 31 cycles, oocytes were randomly allocated to one of seven treatment groups: fixed immediately upon aspiration (0 h group) or after in-vitro maturation culture in the presence or absence of FF-MAS for 22, 30 or 40 h respectively. A total of 81 oocytes were processed for light microscopy. The optimal timing of maturation was observed following 30 h of in-vitro culture, when 67% of FF-MAS-treated oocytes had completed nuclear maturation to the metaphase-II stage compared to 29% in the control group. The maturation time of 30 h appeared significantly superior to both 22 and 40 h, but only in the presence of FF-MAS. Cumulus expansion was most profound in the FF-MAS group after 30 h whereas all oocytes had shed the cumulus investment after 40 h. Our observations indicate that FF-MAS positively influences the absolute frequency and the kinetics of human oocytes undergoing nuclear maturation.