Why Do Women Have Periods? What Are Reasons Of Periods? Periods, also known as menstruation, occur as a natural part of the female reproductive system. They are primarily caused by changes in hormone levels, particularly estrogen and progesterone. These hormones regulate the monthly release of an egg from the ovaries and the thickening of the uterine lining in preparation for pregnancy. If pregnancy does not occur, the body sheds the uterine lining, resulting in a period.Why Do … continue reading...