Amenorrhea is the absence of menstrual bleeding. Amenorrhea is a normal feature in prepubertal, pregnant, and postmenopausal females. In females of reproductive age, diagnosing amenorrhea is a matter of first determining whether pregnancy is the etiology. In the absence of pregnancy, the challenge is to determine the exact cause of absent menses.
Primary amenorrhea is the failure of menses to occur by age 16 years, in the presence of normal growth and secondary sexual characteristics. If by age 13 menses has not occurred and the onset of puberty, such as breast development, is absent, a workup for primary amenorrhea should start.
Secondary amenorrhea is defined as the cessation of menses sometime after menarche has occurred. Oligomenorrhea is defined as menses occurring at intervals longer than 35 days apart.
No consensus has been reached regarding the point at which oligomenorrhea becomes amenorrhea. Some authors suggest the absence of menses for 6 months constitutes amenorrhea, but the basis for this recommendation is unclear. For a post-menarchal girl or a reproductive-aged woman to experience a menstrual cycle interval of more than 90 days is statistically unusual. Practically speaking, this should be an indication for an evaluation to seek the cause.