Comparison of the outcomes of cephalo-caudal to transverse uterine expansion in primary caesarean section: a study protocol for randomized controlled trial

BACKGROUND: Caesarean delivery (CD) is the most common surgical procedure, accounting for nearly forty million childbirths annually. The technique of uterine incision expansion-blunt vertical versus transverse-significantly impacts intra-operative blood loss. This randomized controlled trial (RCT) aims to compare the two techniques to provide evidence-based guidance. METHODS: This single-center, double-blind RCT includes healthy pregnant women (aged 18-40 years, non-anemic) undergoing primary CD at Zhejiang Provincial People's Hospital. Participants are stratified by gestational age (≥ 37 + 0 vs. ≤36 + 6 weeks) and maternal age (≥ 35 vs. <35 years), then randomized 1:1 to cephalo-caudal (vertical) or transverse expansion. The primary outcome will be intra-operative blood loss, evaluated by two surgeons independently during the surgical procedure and further validated through difference between pre-operative and post-operative hemoglobin levels. Secondary outcomes will include lower uterine segment lacerations, additional sutures needed, and uterine vascular injury. The long-term outcome is the uterine niche formation via ultrasound one-year after childbirth. The minimal sample size will be 50 participants in each group to achieve 80% power (α = 0.05). Statistical analysis will be performed via SPSS (version 26.0) or GraphPad Prism (version 9.0). Ethical approval (No. QT2022315) was obtained from Zhejiang Provincial People's Hospital Ethics Board (January 17th, 2025). DISCUSSION: This RCT will compare the novel vertical and conventional horizontal uterine expansion techniques during CD. It will be stratified by maternal age, gestational age and only one surgeon to operate to reduce heterogeneity. The outcomes will include subjective and objective assessment. Despite a relatively small sample size, the study will generate evidence from a nation ranking the top in CD rates to address gaps in CD technique standardization. CONCLUSION: By comparing vertical and transverse uterine expansion, findings will directly inform strategies to minimize surgical blood loss and associated complications. TRIAL REGISTRATION: ChiCTR2200065203. Registered in August 2022, updated in January 2025.