A double-blind investigation into the effects of ritodrine on uterine blood flow during the third trimester of pregnancy.

The object of this double-blind crossover study was to investigate the effect of a beta-mimetic agent-ritodrine-administered intravenously at increasing infusion rates on uterine blood flow and the maternal cardiovascular system during the third trimester of normal pregnancies and pregnancies complicated by intrauterine growth retardation and/or hypertension. Uterine blood flow, maternal arterial blood pressure, maternal and fetal heart rate, and uterine activity were simultaneously recorded throughout the study. In normal pregnancies the changes in different parameters during ritodrine and placebo administration were slight. In the "pathologic" pregnancies there was a highly significant increase in maternal heart rate, differential blood pressure, and uterine blood flow during ritodrine administration. The differences in response to ritodrine and placebo were statistically significant in this later group. This study demonstrates increased sensitivity of the maternal cardiovascular system to this beta-mimetic agent in certain categories of high-risk pregnancies and possibily an increase in uteroplacental blood flow.