During the menstrual cycle, the lining of the uterus builds up in preparation for the fertilization of an egg. If the egg is fertilized, it is implanted in the lining of the uterus. If the egg is not fertilized, the endometrium is shed during the menstrual period. There are several reasons why this shedding of the uterine lining can occur earlier than expected.
Irregular Cycles
When the menstrual cycle first begins, it can be irregular for several years until hormone levels have adjusted. According to the U.S. Department of Health & Human Services, the normal menstrual cycle is 21 to 45 days in teens, and 21 to 35 days in adult women. The length of a cycle is calculated by the number of days between two periods. If a teen has one menstrual cycle that is 32 days in length, she may expect that the next cycle will have a similar length. If the next menstrual period comes after 21 days, it is an early menstrual period but it is still considered normal.
Reproductive Disorders
Some reproductive system disorders can cause irregular menstrual cycles that make it difficult to predict when a menstrual period will occur. Endometriosis is a condition that results in the growth of endometrial tissue outside of the uterus. This condition may contribute to an early menstrual period. Infections of the reproductive system may also cause an early menstrual period, especially if previous cycles were irregular.
Emergency Contraceptives
Emergency contraceptives contain high doses of hormones that work to prevent implantation of a fertilized egg in the lining of the uterus. These hormones can affect the menstrual cycle and cause an early menstrual period. The menstrual cycle may be affected for several months after emergency contraceptives are taken, but should return to normal when hormone levels even out.
Hormonal Changes
The menstrual cycle is regulated by hormones that affect the ovaries and uterus. If these hormone levels surge before the next menstrual period is due, an early menstrual period can occur. An early menstrual period on its own is not a cause for concern. However, an early menstrual period that occurs with pelvic discomfort, pain during intercourse or other reproductive symptoms should be evaluated by a gynecologist to determine if there is a medical condition causing changes in the menstrual cycle.
