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 normal vaginal bleeding that occurs as part of a woman's monthly cycle. Every month, your body prepares for pregnancy. If no pregnancy occurs, the uterus, or womb, sheds its lining. The menstrual blood is partly blood and partly tissue from inside the uterus. It passes out of the body through the vagina.
Periods usually start between age 11 and 14 and continue until menopause at about age 51. They usually last from three to five days. Besides bleeding from the vagina, you may have
Premenstrual syndrome, or PMS, is a group of symptoms that start before the period. It can include emotional and physical symptoms.
Consult your health care provider if you have big changes in your cycle. They may be signs of other problems that should be treated.
NIH: National Institute of Child Health and Human Development
References and abstracts from MEDLINE/PubMed (National Library of Medicine)