Ultrasound-Guided Transversalis Fascia Plane Block Versus Intrathecal Morphine for Post-Cesarean Analgesia: A Prospective Observational Comparative Cohort Study Incorporating a Non-Inferiority Analytical Framework

Background: Intrathecal morphine (ITM) is a widely used reference approach for post-caesarean analgesia but is associated with neuraxial opioid-related side effects, particularly pruritus and nausea. The transversalis fascia plane (TFP) block is a relatively recent regional technique targeting the transversalis fascia; however, comparative effectiveness data in the obstetric setting remain limited. This study aimed to evaluate whether TFP block provides analgesic outcomes broadly similar to those observed with ITM with respect to 24 h rescue analgesic requirement following elective caesarean delivery under spinal anesthesia, and to compare patient-centered recovery quality. Methods: This prospective, single-center, observational comparative cohort study was conducted in a tertiary obstetric unit. Sixty American Society of Anesthesiologists (ASA) physical status II parturients undergoing elective caesarean delivery under spinal anesthesia were included. Postoperative analgesic strategy was determined according to routine clinical practice, with patients receiving either ITM (100 µg) or bilateral ultrasound-guided TFP block with 0.25% bupivacaine. The primary outcome was cumulative tramadol consumption within the first 24 h postoperatively. Secondary outcomes included Numerical Rating Scale (NRS) pain scores at rest and on movement at 0, 3, 6, 12, and 24 h; postoperative nausea and vomiting (PONV) and pruritus scores; and Obstetric Quality of Recovery-11 (ObsQoR-11) scores at 24 and 48 h. A non-inferiority analytical framework was applied to the primary outcome. Results: Both groups had a median tramadol consumption of 0 mg (interquartile range (IQR) 0–0). Rescue analgesic rates were 23.3% (ITM) versus 16.7% (TFP; OR 0.66, 95% CI 0.18–2.36; p = 0.748). Within an exploratory observational non-inferiority analytical framework, the findings were consistent with non-inferiority of TFP block; however, these analyses should be interpreted as hypothesis-generating rather than confirmatory (risk difference −6.7 percentage points; upper 95% CI +13.5% relative to a prespecified margin of +15%). TFP block was associated with higher ObsQoR-11 scores at 24 h (median 96 vs. 88; p = 0.010; Cliff’s δ = −0.39) and 48 h (median 96 vs. 91; p = 0.017; Cliff’s δ = −0.36). Pruritus at 6 and 12 h was nominally lower in the TFP group. Conclusions: In this prospective observational cohort, TFP block was associated with analgesic outcomes broadly similar to those observed with ITM, with exploratory differences in patient-centered recovery measures. Within the applied exploratory observational analytical framework, these findings were broadly consistent with non-inferiority; however, given the observational design, results should be interpreted cautiously, and the present study does not establish formal non-inferiority or equivalence. TFP block may represent a potential opioid-sparing option warranting confirmation in adequately powered randomized studies.