An oocyte is an immature egg, or immature ovum. Oocytes develop to maturity from within a follicle. These follicles are found along the outside layer of the ovaries. During each reproductive cycle, several follicles begin to develop. Normally, only one oocyte each cycle will become a mature egg and be ovulated from its follicle. This process is known as ovulation.
The use of fertility drugs, however, can increase the number of oocytes developing and ovulating as mature eggs. This is the cause for the increased risk of multiple pregnancies when taking fertility drugs. Often, during fertility treatments, the doctor will conduct ultrasounds to monitor follicle growth and oocyte maturation. If too many follicles grow, your treatment cycle may be canceled to prevent the risk of multiple pregnancy or ovarian hyperstimulation syndrome (OHSS).
During IVF, if ultrasound monitoring shows not enough follicle growth, a treatment cycle may be canceled to avoid treatment failure.