Menstruation
Menstruation is the most visible phase of the menstrual cycle and its beginning is used as the marker between cycles. The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days).
Ovarian apoplexy
In the ovaries of sexually mature women, follicles grow, and oocyte matures in them, to prepare for potential fertilization. As a menstrual cycle progresses, a dominant follicle begins to stand out, and in the middle of the menstrual cycle it reaches its maximum size of about 20mm. Then the follicle ruptures, releasing a mature egg (ovulation). The location from which the follicle emerges then forms a temporary cyst, called the corpus luteum, which produces hormones to continue the menstrual cycle and mature the uterine lining. This is the normal ovarian cycle.