Amenorrhea is the transient or permanent absence of menstrual flow. There is no consensus on the definition of amenorrhea, but it may be subdivided into primary and secondary presentations relative to menarche as follows: 
Primary amenorrhea: lack of menses by age 15 years in a patient with appropriate development of secondary sexual characteristics, or absent menses by age 13 years and no other pubertal maturation
Secondary amenorrhea: lack of menses in a nonpregnant female for at least 3 cycles of her previous interval, or lack of menses for 6 months in a patient who was previously menstruating.
Although attributes overlap between the two groups, the diagnostic approaches vary significantly.
The prevalence of amenorrhea is about 3% in women who have previously had regular menstrual periods. The prevalence is higher in college students (3% to 5%), competitive endurance athletes (5% to 60%), and ballet dancers (19% to 44%).  The prevalence of primary amenorrhea in the US is <0.1%, compared with 3% to 4% for secondary amenorrhea.   
Despite the low prevalence of secondary amenorrhea, a prompt, comprehensive assessment is warranted unless the patient is pregnant, lactating, or using hormonal contraceptives, as amenorrhea is often the presenting sign of an underlying reproductive disorder. A delay in diagnosis and treatment may adversely impact the future of such patients. For example, in polycystic ovary syndrome and hyperinsulinemia, behavioral and dietary modifications may prevent subsequent cardiovascular disease.
Associate Professor of Obstetrics and Gynaecology
University of Toronto Faculty of Medicine
Head of Gynaecology and Minimally Invasive Surgery
Sinai Health System
Site Chief of Gynaecology
Women’s College Hospital
MJS reports that he is a consultant for Medtronic, and he is on the advisory boards at AbbVie and Allergan. He has also been a moderator for Bayer.
Department of Obstetrics, Gynecology, and Reproductive Sciences
Division of Reproductive Endocrinology and Infertility
University of Pittsburgh
JSS declares that he has no competing interests.
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