Perimenopause is the natural transition period leading up to menopause. It often begins in a woman’s 40s but can start as early as the mid-30s. During this time, hormone levels — particularly estrogen — can fluctuate, which may lead to changes in menstrual patterns and other physical or emotional changes. Every woman’s experience is different, but some commonly reported signs include irregular or heavier periods, changes in sleep, mood shifts, and hot flushes or night sweats.