Comparison of Two Low-Dose Regimens of Intravenous Fentanyl for Pain Relief During Labor: A Double-Blind Randomized Controlled Trial

Background: Concerns exist regarding the lowest effective dose of opioids in opioid-naïve pregnancies. This study aimed to compare the effectiveness of 25 µg vs. 50 µg fentanyl in relieving labor pain. Methods: In total, 122 term-singleton pregnant females, who planned vaginal delivery, were randomized to receive 25 µg or 50 µg intravenous fentanyl, followed by hourly doses—as needed—for labor pain relief. The primary outcome was the comparison of pain score reduction 30 min after treatment between these regimens. Secondary outcomes included maternal and neonatal safety, total fentanyl dose administered, maternal satisfaction with the fentanyl dosing regimen, and breastfeeding, which were analyzed using appropriate statistical tests. Results: Within-group analysis revealed significant pain score reduction 30 min after fentanyl injection: −1.57 (95% confidence interval, CI −2.1 to −1.1, p < 0.001) and −1.69 (95% CI −2.2 to −1.2, p < 0.001) for 25 µg and 50 µg fentanyl groups, respectively. No significant differences in the pain reduction were observed in between-group comparisons (0.3, 95% CI −0.6 to 1.2, p > 0.999), including secondary maternal and neonatal outcomes. Total fentanyl dose was significantly lower in the 25 µg group compared with the 50 µg group (32.8 ± 13.3 vs. 60.2 ± 22.1, p < 0.001). Conclusions: A 25 µg intravenous fentanyl dose can reduce VAS score, used for evaluating labor pain 30 min after treatment, and is comparable to a 50 µg intravenous fentanyl dose. Given the efficacy of the reduced dosage of fentanyl, this study suggests using 25 µg intravenous fentanyl as an alternative initial dosing for labor pain relief.