Maternal hemodynamic effects of uterine contractions by M-mode and pulsed-Doppler echocardiography.

Nineteen normotensive term gravid women were studied by M-mode and pulsed-Doppler echocardiography to noninvasively evaluate the hemodynamic consequences of uterine contractions on maternal left ventricular function. These laboring subjects were placed in the left lateral decubitus position with epidural labor anesthesia. Ejection fraction was not affected by firm contractions, although a small increase in left ventricular end-diastolic measurements was noted. There was a tendency for maternal heart rate to decrease (-5%); however, this trend was not statistically significant. A 16% increase in left ventricular stroke volume (75 +/- 15 to 89 +/- 17 ml) (p less than 0.001) was associated with an overall 11% augmentation of maternal cardiac output (6.31 +/- 1.79 to 7.12 +/- 1.93 L/min) (p less than 0.001). These findings support the hypothesis that uterine contractions increase maternal stroke volume through autotransfusion of uteroplacental blood and cardiac preload augmentation during normal labor.