Layered precision suturing vs. traditional double-layer closure at cesarean: a randomized trial of uterine scar healing and maternal outcomes

Background Optimal uterine closure at cesarean delivery remains unsettled, as most comparative trials emphasize the number of layers rather than surgical biomechanics. We tested whether a layered precision (LP) suturing technique with quantified tension control improves uterine scar healing compared with traditional double-layer (DL) closure. Methods We conducted a single-center, parallel-group, superiority randomized trial (1:1 LP vs. DL) at a tertiary obstetric hospital. Eligible participants were women aged 20–40 years with a singleton pregnancy at ≥37 weeks of gestation who were scheduled for a first cesarean delivery with a planned low-transverse uterine incision and who provided written informed consent. Participants were randomized using concealed allocation, and cointerventions were standardized. Surgeons were aware of the assigned closure technique, whereas imaging outcome assessors and data analysts remained blinded to the assigned interventions. A total of 500 participants were recruited and randomized. The primary endpoint at 6 months was poor healing on standardized ultrasound, defined as residual myometrial thickness (RMT) 2.2 mm or a uterine niche (indentation ≥2 mm). Secondary endpoints included continuous imaging metrics RMT, 3D scar morphology, MRI diffusion assessed by the apparent diffusion coefficient (ADC), and optional shear-wave elastography, perioperative outcomes, patient-reported outcomes (PROs), and subsequent pregnancy events. Analyses were conducted on an intention-to-treat basis using prespecified adjusted models. Results Of the 500 participants recruited and randomized, primary-outcome data were available for 425 participants (LP 212; DL 213). Poor healing occurred in 16 of 212 participants (7.5%) in the LP group vs. 32 of 213 participants (15.0%) in the DL group absolute risk difference=7.5 percentage points, 95% CI 1.5–13.4; risk ratio (RR) 0.50, 95% CI 0.28–0.89; P = 0.015; adjusted RR 0.50, 95% CI 0.28–0.89. Mean RMT was greater in the LP group (3.05 ± 0.62 vs. 2.78 ± 0.65 mm; adjusted difference 0.27 mm, 95% CI 0.12–0.42; P 0.001) and niche prevalence was lower (12/212 vs. 24/213; RR 0.50, 95% CI 0.26–0.98; P = 0.043). In subset analyses, LP showed higher MRI ADC values (1.18 ± 0.12 vs. 1.12 ± 0.13 × 10⁻ 3 mm 2 /s; difference 0.06, 95% CI 0.02–0.10; P = 0.004) and lower elastography stiffness 28 [24–33 vs. 32 27–37 kPa; difference −4, 95% CI −6 to −2; P = 0.001]. Perioperative outcomes modestly favored LP (median estimated blood loss 480 vs. 520 mL, P = 0.009; operative time 42.5 vs. 45.3 min, P 0.001), with similar rates of fever, infection, and adverse events any adverse event (AE) 42/250 vs. 49/250; serious AE 4/250 vs. 6/250. Conclusion LP closure with quantified tension improved 6-month uterine scar healing across multimodal imaging without introducing new safety concerns, supporting a shift from “stitch count” to a standardized, biomechanics-informed technique.