TREADWAY, J. L. AND J. C. YOUNG. Decreased glucose uptake in the fetus after maternal exercise.Med. Sci. Sports Exerc, Vol. 21, No. 2, pp. 140–145, 1989. Glucose uptake by muscle is stimulated by exercise. However, during pregnancy, insulin resistance develops in maternal skeletal muscle as a mechanism to spare glucose for use by the developing fetus. The purpose of this study was to determine whether a bout of exercise adversely affects glucose availability to the fetus by increasing glucose uptake in maternal muscle tissue. Pregnant (P) and nonpregnant (NP) rats were divided into rest and exercise groups. Immediately following a 50-min treadmill run, a bolus of glucose (1 g·kg-1) and tracer [l-3H]2-deoxyglucose was injected i.v., and rats underwent a 60-min i.v. glucose tolerance test (IVGTT), after which they were sacrificed. Although glucose levels were lower for P vs NP rats at all time points, prior exercise did not affect glucose levels in either P or NP rats. Plasma insulin levels were augmented in P compared with NP rats and were not significantly altered by prior exercise. Glucose/tracer accumulation was enhanced in red and white gastrocnemius in both P and NP rats, and in soleus of NP rats, by exercise. However, glucose/tracer accumulation in the fetus was decreased by 40% (P< 0.01) in the exercised dams. These results indicate that uptake of glucose by the fetus is compromised following exercise, as a result of increased glucose uptake by maternal skeletal muscles.