Efficacy of Propranolol to Reduce Cesarean Delivery in Prolonged Labor: A Randomized Controlled Trial.

Objective: To evaluate the rates of cesarean delivery in patients with prolonged labor randomized to receive intravenous (IV) propranolol compared with placebo.

Methods: A double-blind, placebo-controlled, randomized trial was conducted at two hospitals within a large academic health system. Eligible patients were at 36 weeks or more with a singleton gestation and prolonged labor , defined as: 1) prolonged latent phase of labor (dilation less than 6 cm after 8 hours or more with ruptured membranes and receiving oxytocin infusion) or 2) prolonged active phase of labor (dilation 6 cm or greater and less than 1-cm cervical dilation change over 2 hours or more with ruptured membranes and receiving oxytocin infusion). Patients were excluded for severe preeclampsia, maternal heart rate less than 70 beats per minute, maternal blood pressure less than 90/50 mm Hg, asthma, diabetes requiring insulin during labor, or a cardiac contraindication to β-blockade. Patients were randomized to propranolol (2 mg IV) compared with placebo (2 mL normal saline IV), with one possible repeat dose. The primary outcome was cesarean delivery; secondary outcomes included labor duration, shoulder dystocia, and maternal and neonatal morbidity. With an estimated cesarean delivery rate of 45%, α 0.05, and 80% power, we required 163 patients per group to detect a 15% absolute reduction in cesarean delivery rate. A planned interim analysis was performed, and the trial was stopped for futility.

Results: From July 2020 to June 2022, 349 patients were eligible and approached; 164 were enrolled and randomized, with 84 in the propranolol group and 80 in the placebo group. The rate of cesarean delivery was not different between groups (57.1% propranolol vs 57.5% placebo, relative risk [RR] 0.99, 95% CI 0.76-1.29). Results were similar by subgroup of prolonged latent (n=123) and active (n=41) phases of labor and nulliparous (n=137) and multiparous (n=27) patients. Though not statistically significant, the frequency of postpartum hemorrhage was higher in the propranolol group (20% vs 10%, RR 2.02, 95% CI 0.93-4.43).

Conclusion: In this multisite, double-blind, placebo-controlled randomized trial, there was no difference in cesarean delivery rate for patients who received propranolol compared with those who received placebo for management of prolonged labor.

Clinical Trial Registration: ClinicalTrials.gov , NCT04299438.