ABSTRACT:The preponderance of studies suggest that in physically fit women, physiologic mechanisms have been developed which increase fetal tolerance to the circulatory and respiratory challenges of strenuous maternal exercise. Ventilatory reserve and cardiovascular changes of pregnancy join to protect the fetus in normal pregnancy, and some of these changes are further developed by physical training.The fetal heart rate response to strenuous maternal exercise may provide early diagnosis of uteroplacental insufficiency (UPI). In UPI, the fetal heart rate responds with tachycardia during the exercise, followed by bradycardia for a prolonged period. In preliminary investigations, fetal breathing movements have been more responsive to maternal exercise than have fetal heart rates.