Impact of Menstrual Blood Loss and Oral Contraceptive Use on Oxygen-carrying Capacity.

PURPOSE: The effect of menstrual blood loss on oxygen-carrying capacity remains equivocal. The purpose of this study was to determine the effect of menstrual blood loss on hemoglobin mass in young, healthy women.

METHODS

Twenty-one women (age, 23 ± 6 yr; height, 168 ± 7 cm; weight, 66.1 ± 12.6 kg) with regular menstrual cycles, either using (n = 10) or not using oral contraceptives, participated in the study. Hemoglobin mass was assessed using carbon monoxide rebreathing on three separate occasions over the course of one menstrual cycle.

RESULTS

Visits for women not using oral contraceptives were performed in the early follicular phase (3 ± 1 d after the onset of menses), late follicular phase (1 ± 1 d after the surge of luteinizing hormone in urine), and luteal phase (9 ± 1 d after the late follicular visit). Visits for women using oral contraceptives were performed in the early follicular phase (3 ± 1 d after the onset of menses), late follicular phase (15 ± 3 d after the onset of menses), and luteal phase (9 ± 2 d after the late follicular visit). Hemoglobin mass was not affected by menstrual cycle phase (early follicular, 618 ± 61; late follicular, 610 ± 65; luteal, 607 ± 68 g; P = 0.52). Interestingly, when normalized to weight, hemoglobin mass was 12% higher in women using oral contraceptives in comparison to nonusers (10.0 ± 1.2 vs 8.9 ± 1.2 g·kg, P < 0.05).

CONCLUSION

Menstrual blood loss had no measurable effect on hemoglobin mass in eumenorrheic women. However, oral contraceptive use resulted in a greater oxygen-carrying capacity, potentially leading to a greater maximal oxygen uptake.