Single-Layer Versus Double-Layer Uterine Closure After Primary Cesarean Section

BACKGROUND AND RATIONALE

Cesarean section is one of the most commonly performed surgical procedures worldwide. After fetal delivery, the uterine incision must be closed by suture using one of two accepted techniques: single-layer or double-layer closure. Despite widespread use of both methods : no consensus exists regarding which technique produces superior long-term uterine scar healing.

Poor scar healing can result in a niche. formation (isthmocele), defined as a triangular anechoic indentation of the anterior uterine wall at the scar site with depth greater than or equal to 2 mm (Jordan et al., 2019). Niches occur in 25-70% of women after cesarean section and are associated with postmenstrual spotting, chronic pelvic pain, dyspareunia, fertility impairment, and serious obstetric complications in future pregnancies, including placenta accreta spectrum and uterine rupture.

The residual myometrial thickness (RMT) is the primary ultrasound marker of scar healing quality, defined as the minimum myometrial thickness at the scar site. An RMT below 2.5 mm is associated with a substantially increased risk of uterine rupture in subsequent pregnancies.

Previous studies comparing single-layer and double-layer closure have been limited by heterogeneous populations including scarred uteri, non-standardized surgical techniques, inconsistent ultrasound protocols, and insufficient sample sizes. No study has focused exclusively on primary cesarean sections with a fully standardized operative protocol.

SURGICAL TECHNIQUES

Single-Layer Closure (Group A): The uterine incision is closed with one continuous non-locking suture incorporating the full thickness of the myometrium in one pass, including the decidua.

Double-Layer Closure (Group B): The uterine incision is closed with two successive non-locking extra-mucosal sutures, excluding the decidua. Layer 1 approximates the inner half of the myometrium. Layer 2 buries the first layer, incorporating the outer half of the myometrium and uterine serosa.

All other operative steps are strictly standardized across both groups.

ULTRASOUND ASSESSMENT PROTOCOL

Transvaginal ultrasound (TVUS) is performed by blinded trained sonographers using Samsung HS40 with EVN4-9 probe (4-9 MHz), with empty bladder, preferably in the follicular phase (Day 7-14 of the menstrual cycle), in the mid-sagittal plane.

RMT is measured perpendicular to the serosa at the thinnest scar point. Adjacent myometrial thickness (AMT) is measured 5-10 mm from the scar on both sides. The myometrial ratio is calculated as RM (%) = RMT/AMT x 100.

Niche dimensions (depth, length, width) and volume (ellipsoid formula) are recorded when present.

RANDOMIZATION

Participants are randomized 1:1 using the Clinical Trial Randomization Tool with permuted blocks of variable sizes (4, 6, and 8). Allocation is revealed to the operating surgeon immediately before hysterorrhaphy, after fetal and placentaldelivery. Participants and ultrasound assessors are blinded to group allocation.

STATISTICAL ANALYSIS

Primary analysis uses multiple linear regression for RMT and binary logistic regression for niche prevalence, adjusted for age, BMI, gestational age, uterine exteriorization, surgeon category, and cesarean indication.

Advanced analyses include linear mixed-effects models for repeated measures, Firth penalized logistic regression for predictive modeling, counterfactual mediation analysis (Imai et al.) with bootstrap validation (10,000 replications), inverse probability weighting for loss to follow-up, and five-scenario multiple imputation (MICE).

Software: SPSS v26.0 and R v4.3. Reporting: CONSORT 2010 guidelines.

ETHICAL CONSIDERATIONS

This trial is conducted in accordance with the Declaration of Helsinki (2013), ICH-GCP E6(R2), and Tunisian national regulations. Ethical approval was obtained from the Ethics Committee of the Faculty of Medicine of Sfax (Approval No. 31/26). All participants provide written informed consent. Participation is voluntary and withdrawal is permitted at any time without consequence to medical care.