Why does ovulation become less regular during perimenopause?

During perimenopause, the transition phase leading up to menopause, ovulation becomes less regular primarily due to the declining function of the ovaries.1

As a woman approaches menopause, the number of follicles within the ovaries decreases, and those that remain often fail to mature, rupture, and release an ovum as they did during the reproductive years. This failure to ovulate disrupts the typical menstrual cycle, leading to missed periods, prolonged intervals between cycles, or irregular bleeding patterns. These changes are a normal result of the aging process, which causes an accelerated decline in ovarian function during the years immediately preceding the permanent cessation of menstruation.1