Objective: To measure menstrual blood loss before and during the menopausal transition and to explore the relationships between menstrual blood loss and menstrual cycle irregularity and reproductive hormone levels.

Methods: Two consecutive menstrual blood loss measurements were performed in 77 healthy women aged 21-55 years, classified as midreproductive age (n=21, control group), late-reproductive age (n=17), early-menopausal transition (n=16), and late-menopausal transition (n=23). Serum hormone levels (estradiol [E2], progesterone, follicle-stimulating hormone, luteinizing hormone, and inhibins) were measured three times per week from the start of one menstrual period to the end of the subsequent menstrual period.

Results: There were nine, one, zero, and two anovulatory cycles captured in the late-menopausal transition, early-menopausal transition, late-reproductive age, and midreproductive age groups, respectively. The median (range) menstrual blood loss values after ovulatory cycles were 30 (142), 33 (147), 55.7 (105), and 68.9 (234) mL in the midreproductive age, late-reproductive age, early-menopausal transition, and late-menopausal transition groups, respectively. After anovulatory cycles in the late-menopausal transition group, menstrual blood loss was only 11.8 (97) mL. In the late-menopausal transition group, menstrual blood loss after an ovulatory cycle was significantly higher than when occurring after an anovulatory cycle (P=.008, Kruskal-Wallis). The highest menstrual blood loss measurements were in women in the late-menopausal transition group who experienced ovulatory cycles with abnormally high E2 levels and disturbed E2 secretion patterns.

Conclusion: The onset of variability in menstrual blood loss was associated with the onset of irregular cycles. Excessive menstrual blood loss (greater than 250 mL) was associated with ovulatory cycles with high E2 levels and late menopausal transition.

Level of evidence: III.