Amenorrhea is a common clinical complaint; its frequency varies based on the gynecologic age of the young woman (the number of months or years elapsed since menarche). For example, in a study of high school adolescent girls, the percentage of girls who missed 3 consecutive menstrual periods in a single year was 12.5 in the first year postmenarche and 5.4 after 7 years postmenarche.[1] Traditionally, amenorrhea has been classified as being either primary or secondary. Primary amenorrhea is defined as the failure to initiate menstruation, whereas secondary amenorrhea refers to cessation of menses in an adolescent who has previously menstruated. Although some value can be found in knowing if the absence of menses is due to a disruption or lack of initiation, this distinction is of limited clinical utility because many diseases and clinical states cause both primary and secondary amenorrhea.

The mean age of menarche among girls in the United States has decreased slightly in recent years. In 1973 the average age of menarche was 12.76 among participants in the National Health Examination Survey (NHES). Recent analyses using the combination of NHES and National Health and Nutrition Examination Surveys (NHANES) has documented that the current age of menarche in the United States is 12.54 years, with some variation by race or ethnicity.[2] Further analyses from the NHANES data demonstrated that 90% of girls will have menstruated by age 13.75 years and that fewer than 10% menstruate before 11 years of age.[3]

Amenorrhea is a symptom, not a disease, and has a variety of causes. The differential diagnoses for the patient with amenorrhea includes maturational (constitutional) factors, disorders of the central nervous system (CNS), adrenal and ovarian disease, congenital abnormalities of the reproductive tract (primary amenorrhea), thyroid disease, nutritional disorders, systemic illness, and pregnancy. Therefore a thoughtful, systematic approach to the patient who has a menstrual disorder usually identifies the cause. The major causes of amenorrhea are listed in BOX 161-1.

Menstruation usually begins approximately 2 years after breast budding; however, the interval between the 2 events can be as short as 6 months or as long as 4 years. Given this broad range of individual variation in the onset of puberty and menarche, the physician first must assess pubertal status noting breast and pubic hair development. An evaluation is warranted if:

1. No signs of secondary sexual development are present by 13 years of age. In this instance, the evaluation should include an assessment for delayed puberty. (See Chapter 212, Puberty: Normal and Abnormal.)
2. Menarche has not occurred by 16 years of age even if the patient has experienced development of secondary sexual characteristics and growth has been normal.
3. Three consecutive menstrual cycles are absent, or the patient who has previously menstruated has had amenorrhea for more than 6 months.[4] (See Chapter 212, Puberty: Normal and Abnormal.)

Gynecologic age is important when evaluating an adolescent who appears to have secondary amenorrhea. After the onset of menarche, many teenagers will menstruate sporadically; regular monthly cycles often are not established until 1 to 2 years after menarche.[5] Clearly, the abrupt cessation of menstruation in a teenager who has established regular cycles is of greater concern than the absence of menses for 3 to 4 months in a teenager who has a gynecologic age of 6 months to 1 year. The point at which the clinician elects to pursue an evaluation depends on the anxiety of the patient and her family, the possibility of pregnancy, and the likelihood that a potentially serious disease is responsible for the amenorrhea. For a general approach to the evaluation of amenorrhea, see Figure 161-1 on page 1392.