Menstrual flow occurs due to the cyclical hormonal changes in a woman’s body. The hormones estrogen and progesterone play key roles in regulating the menstrual cycle. In the first half of the cycle, estrogen helps to thicken the uterine lining. After ovulation, if the egg is not fertilized, progesterone levels fall, causing the thickened lining to shed, resulting in menstrual flow.
