[Failures at in vitro fertilization: electron microscopic studies of unfertilized oocytes and undivided ova]

We have examined by electron microscopy the non fertilized oocytes and the non divided eggs after assay of in vitro fertilization. We have observed three blocking points; 1) absence of fusion of the gametes, either because of oocyte immaturity or over-maturity, either because of spermatozoa phagocytosis by follicle cells transformed in phagocytic cells, in presence of intra or extra-cellular bacteria; 2) fusion of the gametes but absence of spermatic nucleus decondensation; 3) fusion of the gametes and pronuclei formation but absence of amphimixy. Two causes are evident: failure of oocyte maturation in vivo or in vitro, and bacterial contamination problems after female or male infra-clinical infections.