Teen Health

The menstrual cycle is the series of changes a woman's body goes through to prepare for a possible pregnancy. Most girls start having periods between the ages of 11 and 15.

A girl who has not had her first period by age 15 has what is called primary amenorrhea. This is different from infrequent or light menstrual cycles, which are very common in teen girls, particularly in the first couple of years after menstruation begins. Primary amenorrhea is also different than if a girl starts having periods, but then stops having periods for at least 3 cycles.

Causes of primary amenorrhea include:

• Problems with the structure of the vagina, such as skin covering the opening of the vagina (imperforate hymen).
• Absence of or an abnormal pelvic organ, such as the uterus or ovaries.
• Very low or very high body weight.
• Eating disorders, such as anorexia, bulimia, or fad dieting.
• Intense exercise.
• Stress.
• Malnutrition.
• Chronic diseases, such as diabetes, anemia, congenital heart disease, or thyroid disease.
• Inherited diseases, such as Turner syndrome.
• A condition that causes a hormone imbalance that interferes with normal ovulation (polycystic ovary syndrome).
• Medicines or medical treatment in childhood that may have damaged the ovaries, such as chemotherapy or radiation treatment for cancer. Chemotherapy or radiation treatment in women may cause irregular cycles.

If no problem can be found to explain why you are not having periods, your doctor may prescribe birth control pills to help control your cycle. These will also help keep your bones strong, reducing your risk for brittle bones (osteoporosis). Your doctor also may prescribe calcium supplements to help ensure that your bones stay healthy.

Girls who have not begun to develop breasts or pubic hair by age 14 may have an increased chance of having amenorrhea.

You can still become pregnant even though you are not menstruating. Practice birth control if you do not wish to become pregnant.