National Institutes of Health
- The primary NIH organization for research on Menstruation is the National Institute of Child Health and Human Development
Menstruation, or period, is a woman's monthly bleeding. Every month, your body prepares for pregnancy. If no pregnancy occurs, the uterus sheds its lining. The menstrual blood is partly blood and partly tissue from inside the uterus, or womb. It passes out of the body through the vagina. Periods usually start around age 12 and continue until menopause, at about age 51. Most periods last from three to five days.
You should consult your health care provider if
Premenstrual syndrome, or PMS, is a group of symptoms that start before the period. It can include emotional and physical symptoms.
Dept. of Health and Human Services Office on Women's Health
References and abstracts from MEDLINE/PubMed (National Library of Medicine)