Eggs begin to grow in follicles on day 5 of the menstrual cycle and ovulate after maturation on day 14 of the menstrual cycle. The two main functions of the ovary are to secrete sex hormones and to produce eggs. There are millions of oocytes in the ovary during the embryonic period and more than 100,000 oocytes left in adulthood, which are encapsulated in primordial follicles and are the basic cells that form the egg. Only one follicle grows to maturity each month during a woman’s reproductive years, and then an egg is released from the ovary, with the mature egg surviving for 12-24 hours. On the 14th day of the menstrual cycle, sperm is sexually discharged and may combine with the egg to form a fertilized ovum that can impregnate. One mature egg is produced by one ovary each month, and both ovaries ovulate alternately. In rare cases, both ovaries ovulate, and sperm combine to form a twin or multiple pregnancy.