Menstruation, the process during which the uterus sheds its lining if pregnancy doesn't occur, starts during the years of puberty, with an average age of 12 years at the time of the first period. The first day that blood is seen counts as the first day of the menstrual cycle. Bleeding usually continues for three to five days, but even two to seven days is still considered within normal range. The hypothalamus, located in the brain, releases a chemical to the pituitary gland, which secretes FSH (follicular-stimulating hormone) and LH (luteinizing hormone), which stimulate the follicles in the ovaries to mature. The follicles release estrogen, which stimulates the build-up and thickening of the uterine lining. If fertilization does not take place, the egg and the uterine lining are sloughed off and menstruation begins.
While some women maintain that they know exactly when they ovulate, as they feel a slight cramping or twinge, most women don't feel anything. Right before ovulation, however, they may notice that their cervical fluid becomes thicker and increases. Around 85 percent of women notice that most of their symptoms occur right before or around the time that their period begins. Almost half of women surveyed complain of menstrual cramps, possibly caused by prostaglandin, a substance that causes uterine contractions. Other symptoms of premenstrual syndrome (PMS) that are caused by hormone fluctuations include diarrhea, headache, irritability, fatigue, moodiness, breast tenderness, feeling bloated, and food cravings, although not every women has every symptom.
Some symptoms can be managed with lifestyle changes, such as cutting down on caffeine, which constricts blood vessels; exercising, which improves blood circulation and reduces cramping; and relaxing your muscles with massage, stress reduction exercises, or meditation. A hot water bottle or heating pad can also soothe the abdominal muscles. Over-the-counter medication is available to treat menstrual symptoms, but if you're having severe cramping or profuse bleeding, you should see your health provider.