Complex interactions among hormones control the start of menstruation during puberty, the rhythms and duration of menstrual cycles during the reproductive years, and the end of menstruation at menopause (which is usually defined as beginning 12 months after a woman's last period). The interactions occur in the following sequence:
Hormones produced by other glands, such as the adrenal glands and the thyroid gland, can affect the functioning of the ovaries and menstruation.
During the reproductive years, vaginal bleeding may be abnormal when menstrual periods are too heavy or too light, last too long, occur too often, or are irregular. Any vaginal bleeding that occurs before puberty or after menopause is considered abnormal until proven otherwise. Most causes of abnormal vaginal bleeding are not serious.
Menstrual disorders include premenstrual syndrome (PMS), menstrual cramps (dysmenorrhea), dysfunctional uterine bleeding, absence of menstrual periods (amenorrhea), and premature menopause. Some disorders that are related to the reproductive organs but not specifically to the menstrual cycle, such as pelvic congestion syndrome and polycystic ovary syndrome, cause some of the same symptoms as menstrual disorders.
Last full review/revision August 2012 by JoAnn V. Pinkerton, MD