In-vitro maturation of human germinal vesicle stage oocytes: role of cumulus cells and epidermal growth factor in the culture medium

In-vitro maturation (IVM) of oocytes is a promising technique to reduce thecosts and avert the side-effects of gonadotrophin stimulation for in-vitrofertilization (IVF). The pregnancy rates from oocytes matured in vitro aremuch lower than those of in-vivo stimulation cycles indicating thatoptimization of IVM remains a challenge. Therefore, we investigated theeffect of supplementation of the medium with gonadotrophins, oestradiol andepidermal growth factor (EGF) and the effect of retaining or removing thecumulus cells on nuclear and cytoplasmic maturation of immature oocytes.Human germinal vesicle (GV) oocytes obtained after gonadotrophinstimulation for intracytoplasmic sperm injection (ICSI) were cultured in acomplex defined medium either supplemented with gonadotrophins, oestradioland physiological concentrations of EGF (2 ng/ml) or gonadotrophins andoestradiol alone. The cumulus cells were either removed or kept intact. InGV stage oocytes cultured without cumulus (group I) significantly moreoocytes reached the metaphase II (MII) stage at 30 h in media supplementedwith EGF (64.3 versus 33.9%, P < 0.003). For oocytes cultured withintact cumulus (group II), more oocytes reached MII at 30 h than in groupI, but there was no difference in medium with or without EGFsupplementation (81.8 and 79.8% respectively). Cytoplasmic maturation ofMII oocytes was judged from their capability to activate and fertilizeafter ICSI. In group I, the rates of activation and normal fertilizationwere similar. However, in group II, significantly more oocytes underwentnormal fertilization in the EGF-supplemented than the unsupplemented group(71.7 versus 45.6%, P < 0.05). The cleavage rates of the fertilizedoocytes were similar in the sibling oocyte subgroups cultured with orwithout EGF supplementation, but the overall cleavage rates were higher incumulus-intact compared to cumulus-denuded oocytes (88.9 versus 47.8%, P< 0.001). Thus, supplementation of the maturation medium with EGF andmaintenance of the cumulus during culture improve the nuclear andcytoplasmic maturation of human oocytes in vitro.