Evaluation of the human fetal cardiac size and function.

Two-dimensional-directed M-mode echocardiography was done on 80 normal fetuses between the 17th to 42nd weeks of gestation. The M-mode beam transected the ventricles at the level of the chordae tendineae at the tip of atrioventricular valves. Right and left ventricular dimensions and free wall thicknesses correlated well with gestational age. Calculated measurements showed a good correlation of the stroke volume and cardiac output with gestational age. The right ventricular dimension, however, was significantly greater than the left ventricular one. Fractional shortening of the right and left ventricle did not change significantly with advancing gestational age. This study indicates that the human fetal right ventricle dimension, stroke volume, and cardiac output are slightly larger than that of the left ventricle. This study also suggests that the human fetus increases its cardiac output to match its growth and it does so by increasing ventricular size rather than fractional shortening or heart rate.