Endometriosis and breakthrough pain during labor epidural analgesia: a matched case-control study 2025-2026

BACKGROUND: We previously identified endometriosis as a potential risk factor for breakthrough pain during labor epidural analgesia in a prospective cohort, but the low prevalence of endometriosis (n = 15) produced imprecise estimates. We aimed to further investigate this association using an enriched sample and a matched case-control design. METHODS: In this matched case-control study at a tertiary maternity center, 36 parturients with confirmed endometriosis were matched 1:3 to 108 controls without endometriosis, based on parity, rapid cervical change, and cervical dilatation at epidural placement. All received standardized labor epidural analgesia. Breakthrough pain was defined as a pain score ≥ 4 despite a functioning epidural, unrelieved by patient-controlled epidural boluses, requiring anesthesiologist intervention. RESULTS: Breakthrough pain occurred in 50.0% of endometriosis patients versus 25.0% of controls (P = 0.007). After adjustment, endometriosis remained independently associated with breakthrough pain (adjusted OR 2.99; 95% CI 1.32-6.72; P = 0.008). Conditional logistic regression confirmed the association (OR 2.00; P = 0.023). CONCLUSIONS: Endometriosis was associated with a higher incidence of breakthrough pain during labor epidural analgesia. These findings warrant confirmation in larger multicenter studies.