A study of the cumulus-corona cell complex in in-vitro fertilization and embryo transfer; a prognostic indicator of the failure of implantation.
In-vitro morphological changes and proliferation of cells of the cumulus oophorus, in particular cells of the corona radiata, were seen to differ between individuals and between oocytes of the same cohort in an unselected series of 159 IVF cycles. Cell proliferation did not relate to indications for treatment, type and length of ovarian stimulation, age of patient, ovarian response and quality of oocyte, fertilization rate or embryo morphology. A direct relationship, however, was demonstrated between the proliferative capacity of these cells and the incidence of clinical pregnancy. No pregnancies resulted when there was an absence of morphological change or proliferation of these cells. In cycles where the proliferative capacity of these cells varied between oocytes of a single cohort the pregnancy rate was 40% per cycle, and in cycles where cells associated with all oocytes underwent extensive proliferation the pregnancy rate was 49% (P < 0.001). Thus, regardless of the apparent quality of gametes or embryo, no pregnancies arose if the cumulus-corona complex was incapable of replication. We have, therefore, identified two populations of oocytes based on the proliferative capacity of cumulus-corona cells in vitro, one being associated with a failure of implantation.