Maternal and fetal cardiovascular response to exercise during pregnancy.

With the two-dimensional Doppler echocardiogram and M-mode echocardiogram, one can study maternal and fetal cardiovascular physiology during rest and exercise. Using such noninvasive techniques, studies indicate that left ventricular function is maintained even during vigorous bicycle exercise in healthy pregnant subjects during the second half of pregnancy. In early pregnancy, the left ventricle adapts to strenuous bicycle exercise by increasing its contractile reserve, enhancing ventricular emptying, whereas in late pregnancy, the left ventricle increases its preload reserve without significantly increasing its contractile reserve. Thus, women are "cardiovascularly" disadvantaged early in pregnancy. Using Doppler signals, early (E-passive) flow and late peak (A-active) flow reflect left ventricular diastolic filling properties. Using such techniques, we found that diastolic filling patterns are significantly influenced by pregnancy and that each trimester influences these diastolic filling patterns during upright bicycle exercise. Doppler studies of uteroplacental circulation during or after exercise have yielded conflicting results. Some have described an increase in "the vascular resistance" of this pelvic bed during strenuous exercise, whereas others have not. It seems safe to conclude that more studies are needed to elucidate this problem. Exercise does not seem to influence the resistivity index of the umbilical artery in either singleton or twins, and may even cause it to decrease. Ventricular diastolic filling properties of the fetal heart do not seem to be influenced by maternal bicycle exercise. Further studies are needed to determine if less active pregnant subjects, women with chronic hypertensive disorders, women with sickle cell anemia, or women with insulin-dependent diabetes adapt to exercise as well as their "normal" counterparts.