Secondary amenorrhea is the absence of menstrual periods for three or more consecutive cycles in a woman who previously had regular periods. This condition can occur due to various factors, including hormonal imbalances, stress, significant weight loss or gain, excessive exercise, and certain medical conditions like polycystic ovary syndrome (PCOS) or thyroid disorders. Diagnosis typically involves a medical history review, physical examination, and possibly blood tests to check hormone levels. Treatment depends on the underlying cause and may include lifestyle changes, medication, or addressing any medical issues contributing to the condition.