The effects of ritodrine infusion on fetal myocardial function and fetal hemodynamics.

The effects of ritodrine infusion on fetal myocardial function and fetal hemodynamics were studied in 18 singleton, healthy, pregnant women with premature uterine contractions. Ritodrine was given intravenously for 2 1/2 h. In 10 cases both M-mode echocardiographs of the fetal heart and measurements of the blood flow in the fetal descending thoracic aorta were made before and after the infusion. No changes took place in the functional parameters or ventricular size of the fetal heart during the infusion. Fetal heart rate increased significantly. In the aorta both the volumetric flow and time-averaged systolic peak, mean and end-diastolic velocities increased significantly, while there were no changes in wave-form indices. In 8 other cases, blood velocity waveform indices were measured by color Doppler flow mapping from the fetal middle cerebral, renal and umbilical arteries. During the infusion the waveform indices decreased significantly in the middle cerebral and renal arteries. There was no change in the indices of the umbilical artery. Ritodrine did not cause any unfavorable changes in the fetal myocardial function or blood flow in the aorta and umbilical artery. The decreased waveform indices in fetal middle cerebral and renal arteries might indicate decreased vascular resistance in these vessels.