For most women, the average menstrual cycle lasts about five to seven days. Some women have shorter periods. If a period is longer than seven days on a regular basis, a doctor should be consulted.
Women start their menstrual cycle in their preteen or early teen years. A woman has one menstrual cycle approximately every 28 days. This continues until the woman reaches menopause, which usually occurs around the age of 50. Women also stop having their periods during pregnancies. A missed period is often a sign of pregnancy. If a woman has abnormal periods, she should consult with a doctor.