Onset of Menstruation

The onset of menstruation (menarche) typically begins around age 12 or 13. However, Menstruation | Additional Resources | Imaginis - The Women's Health & Wellness Resource Network

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Onset of Menstruation

The onset of menstruation (menarche) typically begins around age 12 or 13. However, some girls will begin menstruating a few years earlier or later. Menstruation usually begins approximately two or three years after the first physical signs of puberty appear (such as breast buds or pubic hair). Girls who do not begin menstruating by age 16 should be examined by a physician, although in the majority of cases, there is no cause for concern. Early menstruation (before age 12), late menopause (after age 50), never having children, or having a first child after age 30 can increase the risk of breast cancer

The menstrual cycle is often irregular for the first one to two years. During this time, it is not uncommon for young girls to go three or four months without menstruating. However, over time, the cycle becomes more regular and occurs every 28 days on average (although some women will have shorter or longer cycles).

Recent studies show that girls are beginning to menstruate at an earlier age than previous generations. Researchers are investigating a variety of factors that might influence early menstruation including obesity, environmental estrogens found in chemicals and pesticides, and nutrition.

Length of Menstruation and the Menstrual Cycle

The length of a menstrual cycle varies significantly from woman to woman. The average length is 28 days, although some women have shorter or longer cycles, with a range of approximately 24 to 35 days in 95% of women. The average length of a menstrual period is approximately five days. Again, some women experience shorter or longer periods, with a range of approximately one to eight days. The average blood lost during a period is only two ounces (60 milliliters).

Factors that may change the length of menstruation or menstrual cycles include:

  • Intense exercise
  • Dramatic weight loss
  • Smoking (smokers, especially thin women who smoke, tend to have longer periods)
  • Stress
  • Travel
  • Change in contraception methods
  • Unsuspected pregnancy
  • Early miscarriage
  • Recent childbirth
  • Peri-menopause (the years immediately before menopause)
  • Disorders of the uterus (such as uterine fibroids or endometriosis; see menstrual problems section below)

In addition, studies have shown that when several young women live together and do not take oral contraceptives, they tend to menstruate at the same time of the month. Researchers attribute this synchronization of menstrual cycles to the secretion of pheromones, chemicals that may influence biological activity. Synchronization is disrupted if women live with men.

The Menstrual Cycle

A woman’s menstrual cycle begins each month when the pituitary gland secretes a follicle-stimulating hormone (FSH). This occurs once every 28 days on the first day of bleeding. FSH stimulates a few of the hundreds of reproductive ova (eggs) in one of the ovaries to begin to mature. As an egg matures, the cells around it also grow and form a follicle that releases estrogen. Estrogen is a hormone that stimulates the growth of the uterine lining (the endometrium) to prepare the body for possible pregnancy.

The levels of estrogen and FSH increase for approximately 14 days until the pituitary gland secretes another hormone called luteinizing hormone (LH). LH causes the most mature egg in the ovary to be released around day 14 of the cycle. This act of releasing an egg is called ovulation. Sometimes, more than one egg is released, which can result in twins, triplets, etc. if all of the eggs are fertilized by sperm. When the egg is released from the ovaries, it is guided down one of the Fallopian tubes leading into the uterus.

During this time, the follicle that produces the mature egg (called the corpus luteum) in the ovary will grow and secrete progesterone, a hormone that further prepares the uterus for possible pregnancy. A woman is most fertile during this time, approximately two weeks before she menstruates. If the egg is fertilized during this time, then the woman becomes pregnant. If the egg is not fertilized by a sperm, then it breaks down along with the uterine lining and is discarded during menstruation. Progesterone and estrogen levels also decrease and the corpus luteum is absorbed by the body at this time. The cycle is then repeated.

Phases of the Menstrual Cycle

Follicular Phase Luteal Phase
  • Days 1-14
  • Pre-ovulatory, before the mature egg is released from the ovary
  • Days 15-28
  • Post-ovulatory, after the mature egg is released from the ovary

Physical and Emotional Changes Associated with the Menstrual Cycle

The majority of women experience some physical or emotional symptoms associated with their menstrual cycles (premenstrual syndrome, PMS). Common symptoms may include breast tenderness, bloating, temporary weight gain, irritability, anxiety, etc. Approximately 75% of women experience mild or moderate symptoms as they approach menstruation, while a small percentage experience severe symptoms. The types of symptoms vary significantly from one woman to another and may change over time.

Examples of Premenstrual Symptoms

  • Breast tenderness
  • Bloating
  • Temporary weight gain
  • Headache
  • Backache
  • Fatigue
  • Cramps
  • Intolerance of alcohol
  • Sensitivity to light
  • Acne
  • Diarrhea
  • Throbbing varicose veins
  • Vaginal itching
  • Difficulty concentrating
  • Sleeplessness
  • Food cravings
  • Anxiety
  • Depression
  • Irritability
  • Mood swings
  • Muscle or joint pain
  • Hot flashes


Many premenstrual symptoms can be relieved or improved with lifestyle modifications and over-the-counter medications such as aspirin, ibuprofen, and naproxen sodium. For example, making changes to diet approximately 14 days before a period can help reduce symptoms. Dietary changes may include reducing red meats and dairy products; eating small, more frequent meals; avoiding high fat foods; reducing salt, sugar, and caffeine intake, etc. Vitamin and calcium supplements and exercise may also help alleviate premenstrual symptoms. In some cases, medications such as oral contraceptives, other hormonal therapies, or antidepressants may be necessary.

Approximately 3% to 8% of women experience premenstrual dysphoric disorder (PMDD, also called late-luteal dysphoric disorder). This condition should be evaluated by a physician. Women with PMDD experience severe irritability, depression, and several other symptoms including at least five of the following:

  • Feelings of sadness or hopelessness, possible suicidal thoughts
  • Feelings of tension or anxiety
  • Mood swings marked by periods of crying
  • Persistent irritability or anger that affects other people
  • Disinterest in daily activities and relationships
  • Trouble concentrating
  • Fatigue or low energy
  • Food cravings or bingeing
  • Sleep disturbances
  • Feeling out of control
  • Physical symptoms, such as bloating, breast tenderness, headaches, and joint or muscle pain

Source: The American Psychiatric Association

Though research is ongoing, it is believed that PMDD occurs from a chemical imbalance of serotonin in the body. In some cases, drug therapy such as Sarafem (generic name, fluoxetine hydrochloride) may be helpful. Women who experience severe premenstrual symptoms should discuss treatment options with their physicians.