Mid-Cycle Pain in Endometriosis: Clinical Correlations and Potential Etiological Factors

OBJECTIVE: To characterize differences between individuals with and without mid-cycle pain in a registry cohort with endometriosis. DESIGN: Prospective analysis of data from the Endometriosis Pelvic Pain Interdisciplinary Cohort Data Registry (Clinicaltrials.gov #NCT02911090) at a tertiary referral center in Western Canada. SUBJECTS: Three hundred forty-five individuals aged 18-49 years who: (1) had at least one episode of menstrual bleeding in the last 3 months, (2) attended a baseline initial visit, and (3) subsequently had surgery with histological confirmation of endometriosis between January 2018 and December 2023. Exclusion criteria included (1) previous hysterectomy; (2) hormonal suppressive therapy use in the last 3 months; and (3) missing data on mid-cycle pain, history of hormonal therapy use, or menstrual cycle regularity. EXPOSURES: N/A. MAIN OUTCOME MEASURES: Mid-cycle pain in the last month versus No mid-cycle pain in the last month. RESULTS: Of the 345 participants, 67% (n = 232) reported mid-cycle pain in the last month. Mid-cycle pain in the last month was significantly associated with higher mean Central Sensitization Inventory score (48 ± 17 versus 36 ± 16, p < 0.001) and more months of prior hormonal suppressive therapy use (58 [14-120] versus 26 [0-109], p = 0.012). Abnormal anatomy at the time of surgery (e.g., endometrioma, ovarian adhesions) was not associated with mid-cycle pain in the last month. CONCLUSION: In this endometriosis cohort at a tertiary referral center, most participants reported mid-cycle pain in the last month, which was associated with central sensitization but was not clearly related to endometriosis anatomical distortion.