Exercise in pregnancy : an experimental study of maternal and fetal responses to exercise in sheep

Pregnant women in the western world usually reduce their physical activity as term approaches. However, in recent years increasing numbers of women also voluntarily engage in relatively strenuous exercise during pregnancy. Both pregnancy and physical activity increase the body's metabolic demands, but the physiologic adaptations to these combined demands are only partially understood. On the one hand, one would expect adverse maternal or fetal effects because of the seemingly conflicting demands of the acutely exercising muscles and of the pregnant uterus. On the other hand, however, nature presents several examples in which strenuous physical activity during pregnancy co-exists with a favorable outcome of pregnancy. Therefore, further investigation of the adaptations to exercise in pregnant individuals is important from the viewpoint of physiology as well as of obstetrics. The study of the physiologic effects of exercise during pregnancy is complicated for several reasons. These include 1) large baseline changes within each individual during the course of gestation, 2) wide variation in baseline values between individuals (e.g., physical condition), 3) many differences in exercise load and/or experimental design between studies, 4) wide normal variation in fetal outcome, 5) possible interference off ear and other "stresses", 6) relative inaccessability of the fetus, 7) ethical and legal problems relative to studies in humans, and 8) profound species differences. Many aspects of fetal physiology can only be investigated with the use of invasive techniques. Obviously their use must be restricted to animal studies and, consequently, relatively little is known of the human fetus per se. Although one has to be careful in extrapolating animal data to man, animal studies provide a powerful tool in improving our understanding of human physiology. This thesis represents an effort to obtain a better understanding of the physiologic adaptations to the combined stresses of exercise and pregnancy. It consists of four chapters. Chapter one extensively reviews the literature, discussing the physiologic changes which occur both in pregnancy and exercise, as well as the adaptations to these combined stresses. Rather than to focus on the differences in experimental design and species we emphasize the common denominator in what is known and not known about the subject, and point out fertile topics for further investigation. Chapters two and three present the results of our experimental studies of acute maternal and fetal responses to exercise in chronically instrumented sheep. Finally, chapter four deals with the main physiologic changes during exercise in pregnancy