Renal responses to immersion and exercise in pregnancy.

Twelve healthy pregnant women were studied at 15, 25, and 35 weeks' gestation and at 8 to 12 weeks postpartum. Women were immersed for 20 minutes at 30 degrees C. They then exercised at 60% maximum oxygen capacity on a modified ergometer. Substantial diuresis and natriuresis occurred without changes in osmolarity or serum sodium. The diuresis was significantly greater during pregnancy than postpartum. The natriuresis was similar. Diuresis and natriuresis were greater than would be expected from investigations in nonpregnant subjects. This study suggests that immersion may be a beneficial therapy for edema without decreasing plasma volume.