When do we say that amenorrhea or oligomenorrhea are present?

In several situations, we come across terms related to various types of menstruation-related problems, like amenorrhea, oligomenorrhea, menorrhagia, metrorrhagia, dysmenorrhea, and so on. As one example, the DSM-5 (American Psychiatric Association, 2013) refers to amenorrhea as being commonly present in anorexia nervosa, usually as a result of the weight loss, and notes that it can…