Menarche signals the maturation of an adolescent female. It is a milestone in a young woman's life, and many factors contribute to when it begins. Age and diet, weight, socioeconomic status, and even family structure can all impact when a teenager or pre-teen gets their first period.

First Menstraul Period

Menarche is an adolescent female's first menstrual period. Menstruation is the process of shedding the endometrial lining if the egg released during ovulation was not fertilized — in other words, if the female did not get pregnant. The average length of a cycle is 28 days. In the first two years after menarche, most young women have cycles that last between 21 and 45 days. By the third year, as the body matures, up to 80 percent of young women have cycles between 21 and 34 days long.

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Body Systems Involved

Menarche results from a complex interaction of multiple body systems and hormones. It relies on the normal function of the pituitary gland and the hypothalamus, normal female anatomy, and adequate nutrition. Menarche also depends on interactions between multiple hormones, including those excreted by the thyroid, adrenal glands, and pancreas.

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Average Age of Menarche

The average age of menarche is 12.4 years, but it varies slightly for each adolescent female, depending on many factors, such as race and ethnicity. On average, black girls experience menarche three months sooner than white girls, and girls in southern Europe experience menarche at a younger age than girls in northern Europe. Over the past century, the average age of menarche has gotten younger. Researchers believe that better nutrition in childhood and adolescence contributes to this change. Exogenous hormones in modern-day foods may also play a role.

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Factors Influencing Early Menarche

Early menarche occurs when a girl is younger than nine. Some studies show early menarche is characteristic of girls who live in high socioeconomic status urban households where the mother has a higher level of education. Other studies show that early menarche is associated with the absence of a biological father and a household with step- and half-brothers. Stress and obesity also contribute.

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Factors Influencing Late Menarche

Late or delayed menarche occurs at or after age 15. It can occur in healthy females due to abnormalities in the genitourinary tract. Other causes include poor nutrition and low body weight due to conditions that cause malabsorption, starvation, or anorexia nervosa. Interestingly, the presence of sisters in the home is also associated with late or delayed menarche.

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Birth Characteristics

Some research suggests that age of menarche is also associated with birth characteristics. Birth weight is not the only contributing factor, but girls who were longer than 19.2 inches and weighed more than 6.6 pounds reached menarche earlier than girls who were shorter and lighter. This correlation is even stronger when accounting for other factors, like the mother's nutritional status during pregnancy and socioeconomic factors.

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Adipose Tissue

Adipose or fat tissue also affects menarche. Researchers estimate that girls need at least 17 percent body fat to reach menarche and at least 22 percent body fat to maintain a regular menstruation cycle. Leptin, a hormone made in adipose cells, seems to play a role in maintaining regular menstruation.

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Abnormal Bleeding

Many conditions can cause abnormal uterine bleeding, and they vary in severity. Young women should learn what to expect from their menstrual cycle and how to identify abnormalities. Discovering abnormal patterns early on can help identify many conditions, including polycystic ovary syndrome, thyroid disease, pituitary disease, sexually transmitted diseases, and hypothalamic dysfunction. Some doctors believe that menarche and menstruation in young girls should be used as a vital sign to predict future disease.

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Talking to Adolescents about Menarche

Talking to girls about menarche is essential, but it is not always easy. The biological processes behind it are important, but most young girls care more about practical information. Address topics like how to use sanitary pads and tampons, including how often to change them and the importance of having them on-hand when needed. Talk about what she can expect when starting her period, explaining that periods can last anywhere from three to seven days and that cramping, nausea, and diarrhea are all normal.

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When to See a Doctor

Schedule a medical checkup for girls who have not reached menarche by age 15 or have gone more than three months without a period after beginning menstruation. Other instances that require a doctor's visit are irregular periods, bleeding between periods, periods that happen more frequently than 21 days or less often than 45 days, severe pain, and heavy bleeding that soaks a pad or tampon in one or two hours.

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