Arrested labor secondary to dystocia remains a major indication for acute cesarean section (CS) in many parts of the world. Apart from anatomic problems and malpresentation, the major culprit is uterine dysfunction in the form of weak contractions. Although amniotomy and augmentation with oxytocin are frequently used to augment labor, they have not lessened the frequency of CS. The beta-blocker propranolol, given intravenously, reportedly increases uterine activity, and it has safely augmented labor in a small series of primiparous women. The present study evaluated a combination of intravenous propranolol and oxytocin, compared with oxytocin alone, in women arrested in the first stage of labor.
The study, a prospective, randomized, double-blind trial undertaken at a large university hospital, enrolled 107 women whose first-stage arrest of labor was ascribed to inadequate uterine contractions. All of them received oxytocin infusion and, in addition, were randomized to received either 2 mg propranolol intravenously or placebo in a 10-minute period. A second dose was given after 60 minutes if the cervix remained unchanged. Specialists lacking knowledge of the assigned treatment monitored the fetus by cardiotocography (CTG).
Women given propranolol had no reduction in rates of CS or vacuum extraction. Rates of spontaneous vaginal delivery were 73% and 85%, respectively, in the propranolol and placebo groups, for a relative risk of 0.86 (95% confidence interval, 0.70–1.05). Excluding women having CS, augmented labor constituted 21% of the entire course of labor in the propranolol group and 29% in placebo recipients. The augmented part of labor was 38 minutes shorter in the propranolol group, a difference that was not statistically significant. Before augmentation, the state of the cervix was the same in the 2 groups. Peak oxytocin infusion rates did not differ significantly. Contractions became stronger over time in both groups, but at no time was there a significant group difference. CTG monitoring disclosed 2 cases of transient bradycardia in each group. In addition, 2 infants in the placebo group had decreased variability and 2 others had missing accelerations. There were no significant group differences in heart rate or blood pressure 1 hour after augmentation. Markers of fetal well-being were comparable in the 2 groups. There was no indication of drug accumulation in women given 2 doses of propranolol.