Intravenous Acetaminophen versus Morphine for Analgesia in Labor: A Randomized Trial

Objective  To compare the effectiveness of intravenous acetaminophen with that of morphine in reducing pain in the first stage of labor. Methods  An open-label, randomized controlled trial of women ≥ 34 weeks gestation in the first stage of labor, assigned to either intravenous acetaminophen or morphine. The primary outcome was improved analgesia measured by difference of visual analog scale (VAS) score at 120 minutes from baseline. Secondary outcomes were request for rescue analgesia, maternal side effects, and fetal heart rate changes. Statistical analyses performed were chi-square, Student's t -test, and Kaplan-Meier survival analysis. Results  Of 40 women randomized, 18 received acetaminophen (2 did not receive study drug), and 20 received morphine. Because of difficulties in recruitment, the sample size of 88 was not achieved. The primary outcome was similar between groups ( p  = 0.53). Within 120 minutes of initial treatment, more women receiving intravenous acetaminophen required rescue analgesia (acetaminophen: 52.9% vs. morphine: 17.6%, p Conclusion  There was no difference in VAS scores between groups. However, as half of women receiving intravenous acetaminophen required rescue analgesia within 120 minutes of treatment, intravenous acetaminophen may be less effective for analgesia in early labor compared with intravenous morphine.