Cumulus cells are one of two functionally divided classes of granulosa cells in the antral follicle. They surround the oocyte to form the cumulus-oocyte complex and are released with the egg during ovulation. In order for fertilization to occur, the sperm must penetrate through the layer of cumulus cells. An abundance of cumulus cells is necessary for the development of a healthy embryo, as they provide the necessary nutrients and energy for oocyte maturation.