The common problem of leg edema during pregnancy is usually treated with bed rest and elevation of the affected leg(s). However, recent studies have shown that immersion in water initiates a faster diuresis and provides a more effective treatment than bed rest. Hydrostatic forces are proportional to the depth of immersion, and they force fluid directly into the venous system, bypassing the lymphatics. The rise in central blood volume stimulates the glomerular filtration rate and excretion of water. Because static immersion in deep water for a time sufficient to relieve edema could be uncomfortable and chilling, Kent and colleagues studied the effect of participation in a water aerobics class on leg edema associated with pregnancy.

Healthy pregnant women with uncomplicated singleton pregnancies of 20 to 33 weeks' gestation agreed to participate in the study. The women were 21 to 36 years of age (mean: 30.3 years) and free of medical or obstetric complications, including edema. The women participated in three water aerobic sessions at least 48 hours apart. On the day before testing, participants avoided exercise, immersion of legs in water or ingestion of caffeine and chocolate. Each participant was assessed before and after the three 30-minute sessions. Measurements included body weight, volumetric measurement of the left lower leg, urine output, urinary specific gravity, maternal heart rate, blood pressure and temperature. In random order, each woman was assessed before and after standing on land for 30 minutes or in axilla-deep water for 30 minutes, and before and after participating in a low-impact water aerobics class.

Standing on land produced a mean diuresis of 65 mL, a 46 mL increase in leg volume and a mild reduction in heart rate but no change in urine specific gravity, body weight or blood pressure. Water aerobics and static water immersion were associated with diureses of 187 mL and 180 mL, respectively. These diureses and declines in urine specific gravity were significantly greater than those associated with standing on land. Static water immersion and water aerobics were associated with small decreases in leg volume.

The authors conclude that water aerobics could be beneficial to healthy women with leg edema during pregnancy.