Human Reproduction vol.5 no.7 pp.847-852, 1990 Significance of cumulus oophorus in in-vitro fertilization and oocyte viability and fertility

Fertilization and cleavage rates of human cumulus-intact oocytes incubated in vitro for 36—48 h with normal sperma-tozoa tended to be higher than those which were cumulus-denuded (73 versus 68%; 68 versus 56%, respectively); however, the difference was not significant. Nor were these differences significant when using sperm samples of various qualities (normozoospermic samples: 75 versus 70 % fertilized oocytes; asthenozoospermic: 66 versus 64%; oligozoospermk: 64 versus 56%; oligoasthenozoospermic: 35 versus 33%). The beneficial effect of the human cumulus oophorus on the binding of human spermatozoa to denuded hamster oocytes and on head decondensatkm of human spermatozoa observed after 2 h of incubation (9.3 versus 7.0 bound spermatozoa per oocyte, P < 0.05; 0.5 versus 0.3 decondensed sperm heads per oocyte, P < 0.02) disappeared after 6 h. A protective effect of the cumulus oophorus on hamster oocytes pre-incubated in medium containing 50 % human preovulatory follicular fluid was observed in the sperm penetration assay (fertilization rate of cumulus-intact:cumulus-denuded oocytes, 26 versus 13%, P < 0.05) and confirmed using fluorescein diacetate stain (cumulus-intact oocytes: 86 versus 100 % vitality, non-significant; cumulus-denuded oocytes: 64 versus 100%, P < 0.01). These data suggest the accelerating effect of the human cumulus oophorus on fertilization in its early stages. Furthermore, the cumulus plays an important part in protecting the oocyte against adverse environmental influences. Key words: cumulus oophorus/IVF/oocyte viability/fertilit