It is well known that moderate exercise during pregnancy benefits maternal and fetal well-being. The benefits of more vigorous exercise for pregnant women are less clear. The boundaries of safe exercise during pregnancy remain a matter for continued research, which is important to the growing number of female athletes who plan on becoming pregnant. The purpose of this article is to discuss the existing research related to the physiological concerns of the pregnant endurance athlete specifically. Because endurance training includes prolonged and repetitive exercise bouts at varying intensities, topics will include the effect of high-intensity exercise on uterine blood flow and thermoregulation, metabolic, and musculoskeletal changes in pregnancy.