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Menstrual cycle variability and the perimenopause.
K A O'Connor1, D J Holman, J W Wood
1Department of Anthropology, Center for Studies of Demography and Ecology, University of Washington, Seattle 98195, USA. oconnork@u.washington.edu
Summary
The dwindling ovarian follicle pool, not hypothalamic dysfunction, explains menstrual cycle variability during perimenopause. This finding is based on a new ovarian cycle model predicting changes across reproductive life spans.
Area of Science:
- Reproductive Endocrinology
- Gerontology
Background:
- Menopause is the final cessation of menstrual cycling due to ovarian follicle depletion.
- The perimenopausal transition (1-5 years before menopause) is characterized by increased variability in menstrual cycle length, ovulation frequency, and hormone levels.
- Mechanisms driving perimenopausal cycle changes are poorly understood, with hypotheses including follicle pool size and hypothalamic regulation decline.
Purpose of the Study:
- To investigate the underlying cause of increasing menstrual cycle length variability before menopause.
- To develop and test a model of ovarian cycles explaining perimenopausal changes.
Main Methods:
- A mathematical model of ovarian cycles was developed, incorporating follicular growth, depletion, and an inactive phase before follicular development.
- The model predicts menstrual cycle variability based on the size of the surviving ovarian follicle pool across the reproductive lifespan.
Main Results:
- The model successfully explains key characteristics of the perimenopause in humans and macaques.
- Predictions align with observed increases in menstrual cycle variability as the follicle pool diminishes.
Conclusions:
- The size of the surviving ovarian follicle pool is the primary driver of menstrual cycle variability during the perimenopausal transition.
- The developed model provides a framework for understanding perimenopause and its correlates.