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Menopause marks the end of menstrual cycling associated with loss of ovarian reproductive activity. Natural human menopause is identified retrospectively after twelve months without menstruation, when another cause does not account for the absence. The preceding transition can include irregular cycles and changing ovarian hormone production.^[ref]

A single hormone measurement cannot reliably locate every individual within that transition because concentrations fluctuate. Irregular menstruation during the transition does not itself establish that ovulation has permanently stopped.^[ref]