Supplementary Material for: Effects of Transcutaneous Electrical Nerve Stimulation on Chronic Pelvic Pain in Women: A Systematic Review and Meta-Analysis

Introduction: The study aimed to identify the effects of transcutaneous electrical nerve stimulation (TENS) in women with chronic pelvic pain (CPP) by conducting a systematic review and meta-analysis of randomized controlled trials. Methods: We used five international databases from 2000 to 2020 and selected the clinical trials that reported the effects of TENS on CPP. We excluded the case reports, acute pelvic pain reports, men-related, animal-related, and intravaginal and intrarectal electrical stimulations articles. The level of pain (based on the visual analog scale) was considered for pooling data through the meta-analysis. Results: Ten studies met the inclusion criteria, and three articles were included in the meta-analysis. The results showed that TENS application mildly reduced pain in women with primary dysmenorrhea (mean difference=-1.29; 95% CI: -2.57 to -0.01; Z=1.98, P=0.05). Also, to reduce pain in patients with CPP, the TENS must be applied at least for 20 minutes, with a pulse duration of 50-400 μs, at a frequency of 2-120 Hz. The meta-analysis was followed by assessing the risk of biases, including publication bias. Based on the Cochrane risk of biases evaluation, the majority of the included trials were assessed with moderate methodological quality. Conclusion: TENS application can mildly improve the level of pain in patients with CPP caused by primary dysmenorrhea. Although no distinct agreement was observed among the effective parameters, the high-frequency mode with maximum tolerated intensity was more effective compared to the low-frequency mode.