Effective postoperative analgesia after cesarean delivery is essential for maternal recovery, early mobilization, breastfeeding, and maternal-infant bonding. Although intrathecal morphine (ITM) is considered the gold standard for post-cesarean analgesia, its use is associated with opioid-related adverse effects. Ultrasound-guided lateral quadratus lumborum block (QLB-I) has emerged as a promising alternative. This randomized, double-blind, non-inferiority trial aims to compare the postoperative analgesic efficacy of lateral QLB-I with ITM. Secondary outcomes include postoperative opioid consumption, pain scores, opioid-related adverse effects, quality of recovery (ObsQoR-11T), and maternal satisfaction.

Effective postoperative analgesia following cesarean delivery is essential not only for improving maternal comfort but also for facilitating early mobilization, breastfeeding, and maternal-infant bonding. Inadequate pain control has been associated with delayed mobilization, pulmonary complications, postpartum depression, and the development of chronic postsurgical pain (CPSP).

Intrathecal morphine (ITM) has long been regarded as the gold standard for post-cesarean analgesia, providing effective pain relief for 18-24 hours after a single dose. However, its use is limited by opioid-related adverse effects, including pruritus, postoperative nausea and vomiting (PONV), sedation, and urinary retention. These adverse effects may reduce maternal satisfaction and negatively affect breastfeeding and early mobilization.

In recent years, quadratus lumborum block (QLB) has emerged as an effective alternative for postoperative analgesia in abdominal surgery. Among the various QLB approaches, the lateral QLB-I technique has attracted considerable interest because of its ease of ultrasound-guided application, low incidence of motor block, and potential to provide extensive visceral and somatic analgesia. Previous studies have demonstrated that QLB can effectively attenuate both somatic and visceral pain, with cranial spread of local anesthetic along the thoracolumbar fascia reaching the ventral rami of the thoracic nerves (Blanco, 2015; Elsharkawy, 2019).

Randomized controlled trials in patients undergoing cesarean delivery have shown that QLB reduces postoperative opioid consumption, lowers pain scores, and improves patient satisfaction compared with control groups (Salama, 2020; Zhu, 2021). However, studies directly comparing QLB with ITM remain limited. Current evidence suggests that the analgesic efficacy of QLB may be comparable to that of ITM, although robust evidence demonstrating non-inferiority is still lacking.

Compared with ITM, the principal advantages of lateral QLB include the absence of motor blockade, the potential to reduce opioid-related adverse effects, and facilitation of early mobilization. Although ITM provides potent analgesia, demonstrating that the analgesic efficacy of lateral QLB is clinically equivalent within a non-inferiority margin not exceeding 10 mg intravenous morphine milligram equivalents (IV-MME) would represent a clinically acceptable outcome in terms of patient comfort and safety.

Accordingly, the primary objective of this study is to determine whether lateral QLB-I provides non-inferior postoperative analgesia compared with ITM. Secondary objectives include a comprehensive evaluation of adverse effects, quality of recovery using the ObsQoR-11T, and postoperative opioid consumption.

Inclusion Criteria:

• Women aged between 18 and 45 years.
• Singleton term pregnancy (≥37 weeks of gestation).
• American Society of Anesthesiologists (ASA) physical status II.
• Scheduled to undergo elective cesarean delivery via a Pfannenstiel incision.
• Planned to receive spinal anesthesia for cesarean delivery.
• Provision of written informed consent following a comprehensive explanation of the study.
• Sufficient cognitive capacity to understand and complete the study assessment instruments, including the Numeric Rating Scale (NRS) and the ObsQoR-11T.

Exclusion Criteria:

• Known allergy or hypersensitivity to any of the study medications, including morphine, bupivacaine, or fentanyl.
• Coagulopathy (international normalized ratio [INR] >1.5 or platelet count <100,000/mm³).
• Current treatment with anticoagulant or antiplatelet agents (e.g., heparin, low-molecular-weight heparin, or aspirin >100 mg/day).
• Infection, hematoma, or skin lesion at the planned block insertion site.
• Diagnosis of preeclampsia, eclampsia, or HELLP syndrome.
• Placenta previa, placenta accreta spectrum, or placental abruption.
• Gestational diabetes mellitus or chronic hypertension.
• Emergency cesarean delivery indicated because of fetal distress.
• Conversion to general anesthesia during cesarean delivery.
• History of chronic pain syndrome (e.g., fibromyalgia, lumbar disc herniation, or neuropathic pain).
• Regular use of opioids or psychotropic medications within the preceding 3 months.
• Diagnosis of epilepsy, severe anxiety disorder, or major depressive disorder.
• Obesity (body mass index >35 kg/m²).
• Severe systemic disease, including New York Heart Association (NYHA) class III or IV heart failure, hepatic or renal failure, advanced respiratory disease, or obstructive sleep apnea.
• Advanced pulmonary disease requiring continuous positive airway pressure (CPAP) therapy.
• Inadequate spinal anesthesia or the requirement for supplemental intraoperative analgesia.
• Surgical duration exceeding 120 minutes.
• Excessive intraoperative blood loss (≥1,000 mL) or the need for blood transfusion.

Women aged between 18 and 45 years.

Participants will be randomly assigned in a 1:1 ratio to one of two study groups (lateral QLB-I or ITM). The randomization sequence will be generated by an independent physician using the Research Randomizer web-based application with a block randomization scheme employing a fixed block size of four. Group allocations will be placed in sequentially numbered, opaque, sealed envelopes identified only by the participant's randomization number. The envelopes will be stored in a locked cabinet and opened on the day of surgery by an anesthesia nurse who is not otherwise involved in the randomization process or study conduct. All study personnel, including the participant, surgeons, and outcome assessors, will remain blinded to treatment allocation; only the anesthesiologist administering the spinal anesthesia will be aware of group assignment.