Why the study?
Accurate estimates of pregnancy-related plasma volume expansion require correct timing and measurement in nonpregnant women, but consensus on plasma volume patterns across the menstrual cycle was lacking.
Does plasma volume vary significantly across the menstrual cycle in healthy women of reproductive age?
Does plasma volume vary significantly across the menstrual cycle in healthy women of reproductive age?
Plasma volume variations across the menstrual cycle are small, suggesting the cycle phase may not be an important consideration when evaluating plasma volume in women of reproductive age.
Small plasma volume variations across phases may not require cycle timing adjustment in healthy women; leaves open relevance in clinical populations.
Increases in reproductive hormones like estrogen, play an important role in the remarkable increases in plasma volume observed in pregnancy. Accurate estimates of plasma volume expansion during pregnancy depend on correctly timing and measuring plasma volume in nonpregnant women. However, to date, there is no consensus on the pattern of plasma volume across the menstrual cycle. We prospectively measured plasma volume in 45 women across a single menstrual cycle. A urine-based fertility monitor was used to time three clinic visits to distinct points in the menstrual cycle: the early follicular phase (~day 2), periovulation (~day 12), and the mid-point of the luteal phase (~day 21)-based on a 28-day cycle length. Healthy women aged 18-41 years with regular menstrual cycles and a healthy body weight were enrolled in the study. At each visit, blood samples were collected before and after injection of 0.25 mg/kg body weight of indocyanine green dye (ICG). Pre- and post-ICG injection plasma samples were used to measure plasma volume. Preinjection samples were used to measure ovarian hormones and plasma osmolality. Mean plasma volume was highest during the early follicular phase (2,276 ± 478 ml); it declined to 2,232 ± 509 ml by the late follicular phase and to 2,228 ± 502 ml by the midluteal phase. This study found that overall variations in plasma volume are small across the menstrual cycle. Therefore, in clinical practice and research, the menstrual cycle phase may not be an important consideration when evaluating plasma volume among women of reproductive age.
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Aguree et al. (2020) studied this question.
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