Effects of maternal exercise on fetal and maternal respiration and nutrient metabolism in the pregnant ewe.

Pregnant ewes (122-137 days gestation) were studied while standing at rest and while walking on a treadmill at 0.4 m.s-1 on a 10 degree slope for 60 min (mild exercise) or 0.7 m.s.-1 on a 10 degrees slope for 60 min (moderate exercise). Maternal and fetal blood gases, pH and packed-cell volume, and arterial concentrations of haemoglobin (Hba), glucose, lactate and acetate were measured. Net uterine uptake of oxygen, glucose, lactate and acetate was calculated from measurements of uterine blood flow and arteriovenous concentration differences. During mild exercise there were small increases in maternal arterial oxyhaemoglobin saturation (SaO2) and Hba, accompanied by mild hypocapnoea, and a 34% increase in fetal arterial glucose concentration. During moderate exercise there were significant increases in maternal SaO2. Hba and Pha, and a decrease in PaCO2; fetal pHa increased and PaCO2 decreased, although not to the same extent as in maternal blood, and there were 25% and 18% decreases in fetal PaO2 and SaO2, respectively. Both maternal and fetal arterial glucose and lactate concentrations increased substantially. Uterine blood flow decreased by 36% but there was a simultaneous increase in the net uterine extraction of oxygen and glucose from arterial blood, so that net uterine uptakes of oxygen and glucose were not significantly affected by moderate exercise. The results suggest that fetal oxygenation is compromised by the effects of reduced uterine blood flow and maternal alkalosis on placental oxygen transfer. Possible reasons for the exercise-induced fetal hyperglycaemia include increased umbilical glucose uptake, stimulation of glycogenolysis in fetal liver and reduced fetal glucose utilization, and latter two possibilities as consequences of fetal hypoxaemia.