Menstruation refers to the periodic vaginal discharge of blood and bodily cells that are shed from the lining of a woman's uterus. Menstruation begins at puberty and marks the onset of a woman's capacity to bear children, although other health factors may limit this capacity.

Menstruation usually begins between 10 and 16 years of age, depending on a variety of factors, including the young woman's general health, nutritional status, and body weight relative to height.

Menstruation continues approximately once a month until a woman is about 45 to 50 years of age, again depending on health and other influences. The end of a woman's ability to menstruate is called menopause and it marks the completion of a woman's childbearing years.

Length of the Menstrual Cycle

The average length of the menstrual cycle is 28 days, but ranges from 21 to 40 days. The length of the cycle may also vary for a woman during different phases of life, and even from one month to the next depending on a variety of factors, including the woman's physical, emotional, and nutritional health.

Menstruation is part of the regular process that prepares a woman's body each month for pregnancy. This cycle involves several phases that are controlled by the interactions of hormones secreted by the hypothalamus, anterior pituitary gland, and ovaries.

At the beginning of the cycle, the cell lining of the uterus begins to develop and thicken. This lining will serve as the anchor for the developing fetus if the woman is impregnated. Hormones signal an ovum or egg in the ovary to begin developing. Soon, an ovum is released from the woman's ovary and begins to move through the Fallopian tube toward the uterus.

If the ovum is not fertilized by a sperm during the course of vaginal intercourse (or through artificial insemination), however, the lining of the uterus separates from the uterine wall and begins to decompose. The blood system washes the lining away and it and the blood are discharged through the woman's vagina.

The period of discharge or bleeding, known as the menstrual period (or just "period"), lasts from three to seven days. If a woman becomes pregnant, her monthly menstruation ceases for the duration of the pregnancy. Consequently, missing a menstrual period is a likely although not a definitive sign that a woman is pregnant. Pregnancy can be confirmed with a simple blood test.

First Menstruation — A Potentially Upsetting Time for Girls

Unless a girl has been prepared for the onset of menstruation, this can be an upsetting time. Girls who are ignorant of their body and normal reproductive processes may assume that menstruation is evidence of a disease or even a punishment for misbehavior. Girls who are not taught to think of menstruation as a normal body function may experience considerable shame and a feeling of being unclean during their first menstruation. Even when menstruation is finally recognized as a normal process, feelings of uncleanliness may linger well into adulthood.

In recent years, however, better education about anatomy and physiology has led to acceptance of menstruation. In fact, many women have come to view menstruation with pride as a distinctly female process. Some families even have a private celebration to honor the maturation of the young woman.