Final answer:
Secondary amenorrhea is the cessation of menstrual periods in a woman who has previously menstruated, possibly caused by factors such as hormonal imbalances, breastfeeding, stress, and nutritional deficiencies.
Step-by-step explanation:
Secondary amenorrhea is a term that refers to the absence of menstrual periods in a woman who has previously menstruated. This condition indicates that a woman has stopped having menses for three months or more if her cycles were previously regular, or for six months or more if her cycles were irregular. There are various causes for secondary amenorrhea, such as pregnancy, the amenorrhaeic effect of breastfeeding, hormonal imbalances, stress, nutritional deficiencies, and certain medical conditions. The onset can be related to issues with the reproductive system such as the ovaries or can be due to pituitary defects, which affect hormone levels vital for menstruation. It is distinct from menopause, which is the natural conclusion of menstrual periods around the age of 50. Furthermore, secondary amenorrhea should not be confused with an anovulatory menstrual cycle, which occurs when an ovary does not release an egg during a cycle, but menses may still occur.