Gynecology - Menstrual Cycle
The Menstrual Cycle
Menstruation is a woman's monthly bleeding. It is also called menses, menstrual period, or period. When you have a period, you are menstruating. The menstrual blood is actually partly blood and partly tissue. It comes from the inside of the uterus (womb). It flows from the uterus through the small opening at the lower part of the uterus called the cervix. The blood passes out of the body through the vagina. Sanitary pads or tampons, which are made of cotton or another absorbent material, are worn to absorb the blood flow. Most menstrual periods last from 3 to 5 days.
Menstruation is part of the menstrual cycle, which helps your body prepare for the possibility of pregnancy each month. A cycle starts on the first day of a period. The average menstrual cycle is 28 days long. However, a cycle can be shorter or longer than this. It may be anywhere from 23 days to 35 days.
At about day 14 of a typical 28-day cycle, in response to a surge of luteinizing hormone, the egg leaves the ovary. This is called ovulation.
During the second half of the menstrual period the egg begins to travel through the fallopian tube to the uterus. If the egg becomes fertilized by a sperm cell and attaches itself to the uterine wall, you become pregnant. If the egg is not fertilized, it either dissolves or is absorbed into the body. Estrogen and progesterone levels drop, and the thickened lining of the uterus is shed during the menstrual period at the end of the cycle.
Your period may not be the same every month, and it may not be the same as other women's periods. Periods can be light, moderate, or heavy. The length of the period can also vary. Most menstrual periods last from 3 to 5 days, but anywhere from 2 to 7 days is considered normal. The amount of blood lost is usually only about 2 to 5 tablespoons over the entire period. Some women experience abnormal uterine bleeding that should be evaluated by a physician.
Most women can tell their period is coming because they experience some breast tenderness and pelvic discomfort. These symptoms, sometimes referred to as PMS or pre-menstrual syndrome, can occur before, during, or after your period. Sudden mood changes are not unusual. Bloating, tiredness, and headaches may occur.
For the first few years after a girl starts menstruating, periods may be very irregular. They may happen anywhere from once a month to 3 times a year. They may also become irregular in women approaching menopause during middle age.
ACOG.org for more information.
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