Effects of Acupuncture on Uterine Hemodynamics and Early-Phase Pain Relief in Primary Dysmenorrhea: A Retrospective Cohort Study

Background: Primary dysmenorrhea is fundamentally driven by uterine ischemia resulting from excessive vascular resistance. While acupuncture is theorized to improve perfusion, high-quality evidence controlling for pharmacological confounders is limited. This study aimed to evaluate the hemodynamic effects and longitudinal analgesic efficacy of the “Regulating Ren and Unblocking Du” acupuncture protocol. Methods: This retrospective cohort study analyzed data from 286 patients treated between 2020 and 2024. To minimize selection bias, a 1:1 Propensity Score Matching (PSM) algorithm was applied to balance baseline covariates, including medication regimen (NSAIDs vs. hormonal therapy), disease severity, and age at menarche. The final matched cohort included 158 patients (79 pairs). The intervention group received acupuncture plus conventional medication, while the control group received medication alone. Primary outcomes included uterine artery Doppler indices (Pulsatility Index [PI], Resistance Index [RI], S/D ratio) and Visual Analogue Scale (VAS) pain scores assessed at 1, 3, and 6 months. Results: Post-treatment, the acupuncture group exhibited significantly lower vascular resistance compared to controls, with a mean difference of − 0.54 (95% CI: − 0.66 to − 0.42) for PI and − 1.7 for the S/D ratio (p < 0.001). Clinically, acupuncture provided superior rapid analgesia; at 1 month, VAS scores were significantly lower in the intervention group compared to controls (p < 0.001). This advantage persisted at 3 months but converged by 6 months (p = 0.32), indicating a diminishing differential effect over time. Subgroup analyses revealed enhanced efficacy in patients aged < 30 years or with a disease duration < 5 years. Minor adverse events occurred in 6.3% of acupuncture recipients. Conclusion: After rigorously adjusting for confounders, acupuncture was associated with reduced uterine arterial resistance. Clinically, it offers a distinct “window of opportunity” for rapid symptom control in the early treatment phase, particularly for younger patients. Plain Language Summary : This study evaluated whether adding a specific acupuncture technique, called “Regulating Ren and Unblocking Du” to usual medication improves uterine blood flow and pain in women with menstrual cramps without underlying disease. In this review of 158 patients, one group received acupuncture plus medication and the other received medication alone. The acupuncture group showed greater improvement in uterine blood flow and greater pain reduction in the short term up to three months, especially in younger patients and those with a shorter pain history. However, the added benefit of acupuncture diminished after six months. Acupuncture is safe, with only minor side effects such as mild bruising or temporary dizziness. In conclusion, this acupuncture approach can enhance short-term blood flow and pain relief when combined with conventional treatment; however, its effects may not be sustained long-term without ongoing sessions. Keywords: primary dysmenorrhea, acupuncture, uterine blood flow, pain relief, retrospective study