After eligibility assessment and obtaining written informed consent, eligible participants will be randomly allocated to one of the two study groups in a 1:1 ratio.
The random allocation sequence will be generated by an independent person who is not involved in patient recruitment, intervention administration, outcome assessment, or data analysis, using a computer-generated random number sequence. Block randomization with variable block sizes will be used to maintain balance between the two study groups.
Allocation concealment will be ensured using sequentially numbered, opaque, sealed, light-proof envelopes. Each envelope will be opened only after the participant has been definitively enrolled in the study and immediately before preparation of the study medication. Study medications will be prepared by an independent person and provided in identical syringes with coded labels, similar in appearance and volume.
Participants, the anesthesiologist performing the TAP block, postoperative care staff, outcome assessors, and the statistician will remain blinded to group allocation.
This study is designed as a double-blind randomized clinical trial. Participants, the anesthesiologist performing the TAP block, postoperative care staff, outcome assessors, and the statistician will remain unaware of participants’ group allocation.
The allocation sequence and group codes will be generated and kept by an independent person who is not involved in patient care, intervention administration, data collection, outcome assessment, or statistical analysis. Study medications will be prepared by the same independent person, or by a trained pharmacist/nurse who has no role in patient assessment or data analysis. For each participant, the study medication will be prepared according to the randomization code in identical syringes with similar volume, appearance, and coded labeling. The syringes will be labeled only with the study code and participant number, and the name of the medication will not be written on the syringe.
In both groups, the final injected volume for the TAP block will be identical, and the study solutions will not be distinguishable by appearance. Bilateral TAP block will be performed in both groups using the same technique, at the same anatomical site, with the same injection volume, and under ultrasound guidance. Therefore, the participant, the anesthesiologist performing the block, and the outcome assessor will not be able to identify the treatment group.
Assessment of pain intensity, duration of analgesia, time to first request for rescue analgesia, rescue analgesic consumption, maternal satisfaction, and adverse events will be performed by an assessor blinded to group allocation. Data will be entered into the statistical software using coded group labels, such as Group A and Group B, and the statistician will remain blinded to the actual intervention assigned to each group until completion of the primary analysis.
Allocation codes will remain confidential until completion of data collection and primary statistical analysis. In case of a serious adverse event or emergency situation in which knowledge of the administered study medication is necessary for patient management, unblinding for that individual participant will be permitted by the principal investigator or the study safety supervisor. The reason, time, and person responsible for unblinding will be documented and reported.