Amenorrhea Definition
Amenorrhea is the absence or abnormal cessation of menstrual periods, classified as primary amenorrhea (failure to reach menarche by age 15 or within 3 years post-thelarche) or secondary amenorrhea (cessation of previously regular menses for 3 months or previously irregular menses for 6 months). 1, 2
Primary Amenorrhea
Primary amenorrhea refers to the lifelong absence of menses and requires evaluation when:
- Menarche has not occurred by 15 years of age, OR
- Menarche has not occurred within 3 years after breast development (thelarche) 1
This condition is often caused by chromosomal abnormalities leading to primary ovarian insufficiency (such as Turner syndrome) or anatomic abnormalities like Müllerian agenesis 2.
Secondary Amenorrhea
Secondary amenorrhea is defined as the cessation of menstruation in women who previously had periods. The diagnostic threshold is:
- 3 months of absent menses in women with previously regular cycles, OR
- 6 months of absent menses in women with previously irregular cycles 1, 2
Important Clinical Context
The Endocrine Society guidelines specifically recommend diagnostic evaluation for functional hypothalamic amenorrhea (FHA) when:
- Menstrual cycle intervals persistently exceed 45 days, AND/OR
- Amenorrhea is present for 3 months or more 3
This is particularly relevant because menstrual cycles in adolescents typically do not exceed 45 days, even during the first postmenarchal year 3.
Key Clinical Pitfall
Always exclude pregnancy first in any patient presenting with amenorrhea, regardless of whether it appears to be primary or secondary 1, 2. This is the most critical initial step before pursuing other diagnostic evaluations.
The absence of menses can result from outflow tract abnormalities, primary ovarian insufficiency, hypothalamic or pituitary disorders, other endocrine disorders, chronic disease sequelae, physiologic causes, or iatrogenic factors 1.