At what stage of the menstrual cycle does perimenopause generally begin?

Perimenopause is characterized as the transition phase leading up to menopause, during which the body undergoes significant hormonal fluctuations. This stage does not have a specific onset related to a particular point in the menstrual cycle, such as ovulation or menstruation. Instead, perimenopause can start at various times for different individuals, often marked by irregularities in menstrual cycles, changes in menstrual flow, and other symptoms associated with hormonal changes. These variations make it difficult to pinpoint a specific stage within the cycle when perimenopause begins.

In contrast, ovulation and menstruation refer to specific, defined times within the menstrual cycle when certain hormonal processes occur, but perimenopause introduces variability in these processes, indicating that its onset can be anytime with respect to the cycle. Menopause, defined as having occurred after 12 consecutive months without menstruation, is a distinct phase that follows perimenopause, further emphasizing that perimenopause itself can occur at various times in a woman's life, often several years before menopause actually begins.