Preoperative Melatonin for Women Undergoing Cesarean Section: A Systematic Review and Updated Meta-Analysis of Randomized Controlled Trials with Trial Sequential Analysis

Introduction: Effective perioperative management in cesarean section remains essential to optimize maternal outcomes. Melatonin (M) has been proposed as a potential adjunct due to its analgesic, anxiolytic, and antiemetic properties; however, evidence from randomized controlled trials (RCTs) remains inconsistent. This meta-analysis aimed to evaluate the efficacy and safety of preoperative melatonin compared with placebo in women undergoing cesarean section. Methods: A systematic search was conducted in PubMed, Scopus, and Cochrane from inception to 15 March 2026 for studies evaluating pregnant women undergoing elective cesarean section receiving preoperative melatonin versus placebo (P) (PROSPERO “CRD420261355468”). Heterogeneity was assessed using the I² statistic and Cochrane Q test. Risk ratios (RRs) and standardized mean differences (SMDs) were computed using a restricted maximum-likelihood estimator random-effects method. Trial Sequential Analysis (TSA) was performed to assess the robustness and sufficiency of the evidence. Results: Seven RCTs were included with 552 patients (melatonin: 278; placebo: 274). Preoperative melatonin significantly reduced opioid consumption in the overall pooled analysis (RR 0.31, 95% CI 0.12 to 0.80; p = 0.030; I² = 50%), and TSA supported the robustness of this opioid-sparing finding under the selected assumptions. Postoperative pain scores were also significantly lower in the melatonin group (SMD −2.10, 95% CI −2.43 to −1.78; p < 0.01; I² = 22%). The incidence of postoperative nausea showed a trend toward reduction in the conventional meta-analysis (RR 0.49, 95% CI 0.23–1.04; p = 0.057; I² = 34%); although TSA suggested a possible benefit, this finding should be considered exploratory. No significant difference was observed in intraoperative blood loss (SMD −0.33, 95% CI −1.53 to 0.88; p = 0.60; I² = 94%). Conclusions: Preoperative melatonin may be a promising adjunct in cesarean section, particularly for reducing postoperative pain and overall opioid consumption. TSA findings support the opioid-sparing result under selected assumptions, while the possible effect on postoperative nausea remains exploratory. Further high-quality trials are warranted before routine clinical implementation can be recommended.