In your menstrual cycle, the hypothalamus, the anterior pituitary, and the ovaries interact to result in ovulation. In general, this process repeats itself approximately every 28 to 30 days in four phases. The first phase of the cycle is the three to seven days of menstruation. The first day you start menstruating is the first day of your cycle. When the end of menstruation is near, one of the ovaries begins to prepare an egg, also called an ovum, to be released into one of the fallopian tubes. The lining of the uterus, the endometrium, begins to thicken in preparation for a fertilized egg. The third step, called ovulation, happens around day 14 of a 28-day cycle. A mature egg is released from the ovary and enters the fallopian tube. The fourth and final phase is marked by the egg's journey down the fallopian tube. The endometrius continues to thicken. If the egg isn't fertilized by a sperm cell, it disintegrates. The thickened lining of the uterus isn't needed, so it's shed by the body. This is your period, or menstruation, and the cycle begins all over again. If the egg is fertilized at the time of ovulation, it enters the uterus, latches onto the lining, and begins to grow.