EFFECTS OF CHRONIC EXERCISE ON BLOOD-VOLUME EXPANSION AND HEMATOLOGICINDEXES DURING PREGNANCY

Objective: To compare blood volumes and hematologic indices between ni ne aerobically trained, physically active pregnant women who continued to exercise throughout gestation and five healthy yet sedentary gravi das. Methods: Subjects were tested on three occasions: 25 and 36 weeks of pregnancy and 12 weeks postpartum. Plasma volumes were estimated b y dye dilution with Evans blue. Blood samples were taken from the ante cubital vein with the subjects resting in a seated, semirecumbent posi tion. In addition to plasma volume estimations, blood samples were ana lyzed for hematocrit ratio, hemoglobin concentration, red cell count, and plasma protein concentration. Blood volumes and red cell volumes w ere calculated from plasma volume estimates and hematocrit ratios. Res ults: Average birth weight and length of gestation did not differ betw een the subject groups. Analysis of variance indicated that absolute b lood volume measures were significantly greater (P <.01) in the physic ally active compared to sedentary subjects at all three test times. Si milar results were found for plasma and red cell volumes (P <.01). Blo od volumes relative to body weight were significantly higher in physic ally active subjects (P <.01) than in their sedentary counterparts at 25 weeks (88.5 versus 75.5 mL/kg) and at 36 weeks (88.4 versus 70.9 mL /kg), as well as at 12 weeks postpartum (72.2 versus 57.6 mL/kg). All vascular volumes were significantly (P <.001) lower at 12 weeks postpa rtum compared to those seen during pregnancy in both subject groups. H ematologic indices of hematocrit ratio, hemoglobin concentration, red cell count, and plasma protein concentration were all greater (P <.001 ) at 12 weeks postpartum than during pregnancy. Conclusions: Physicall y active women possessed significantly greater vascular volumes than t heir sedentary counterparts. Although this difference was maintained t hroughout gestation as the active gravidas continued to exercise, ther e was no apparent effect on pregnancy outcome.