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

Single-Layer Versus Double-Layer Uterine Closure After Primary Cesarean Section: Impact on Residual Myometrial Thickness and Cesarean Scar Defect Formation - A Prospective Randomized Controlled Trial

This study compares two surgical techniques for closing the uterus after cesarean section: single-layer versus double-layer closure. The primary objective is to determine which technique results in better uterine scar healing, measured by residual myometrial thickness (RMT) and cesarean scar defect (niche) prevalence at 6 weeks and 6 months postoperatively.

BACKGROUND:

Cesarean section is one of the most common surgeries worldwide. After fetal delivery, the uterine incision must be closed by suture. Poor scar healing can lead to niche formation, abnormal bleeding, pelvic pain, dyspareunia, and complications in future pregnancies including uterine rupture and placenta accreta.

INTERVENTION:

Participants are randomized 1:1 to receive either:

• Single-layer closure: one continuous non-locking suture through full myometrial thickness
• Double-layer closure: two successive extra-mucosal non-locking sutures excluding the decidua

ASSESSMENTS:

Transvaginal ultrasound at 6 weeks and 6 months measures RMT and niche presence. Standardized symptom questionnaires assess pelvic pain, spotting, dysmenorrhea, and dyspareunia.

ELIGIBILITY:

Women aged 18-45 years undergoing primary cesarean section with singleton pregnancy at term (gestational age ≥ 37 weeks).

ENROLLMENT: 384 participants (192 per group)

SETTING: Department of Obstetrics and Gynecology, Hedi Chaker University Hospital, Sfax, Tunisia

FOLLOW-UP: 6 months per participant in which the patients attend 2 follow-up visits:

First visit 6 weeks after surgery. Second visit at 6 months after surgery

.And have a pelvic ultrasound at each visit

Study Overview

• Status: Completed
• Conditions: Pelvic Pain; Metrorrhagia; Amenorrhea Secondary; Spotting; Cesarean Scar Defect (Isthmococele)
• Intervention / Treatment: Procedure: Single-layer hysterorrhaphy at primary cesarean section; Procedure: Double-layer hysterorrhaphy at primary cesarean section

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Actual): 384
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Tunisia
  • Sfax Governorate
    • Sfax, Sfax Governorate, Tunisia, 3000
      • Hedi Chaker university hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Women aged 18 years or older
• Singleton pregnancy
• Gestational age ≥ 37 weeks (term pregnancy)
• Scheduled or emergency primary cesarean section (first cesarean delivery, no previous uterine scar)
• Low transverse uterine incision (Pfannenstiel or Joel-Cohen approach)
• Ability to provide written informed consent
• Willingness to attend follow-up visits at 6 weeks and 6 months postoperatively
• Patient affiliated to a social security system or equivalent healthcare coverage

Exclusion Criteria:

• Previous uterine surgery (prior cesarean section, myomectomy, uterine perforation, or any procedure leaving a uterine scar)
• Multiple pregnancy (twins or higher-order multiples)
• Preterm delivery (gestational age < 37 weeks)
• Classical (vertical) or inverted T uterine incision
• Placenta previa or placenta accreta spectrum disorder
• Active uterine infection or chorioamnionitis at time of surgery
• Coagulation disorders or anticoagulant therapy
• Immunosuppressive therapy or conditions affecting wound healing (systemic corticosteroids, immunosuppressants)
• Severe maternal comorbidities (uncontrolled diabetes, connective tissue disorders, chronic renal failure)
• Participation in another interventional clinical trial
• Patient unable to attend scheduled follow-up visits
• Patient unable to understand or sign informed consent
• Fetal demise or major fetal malformation

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Single-layer Uterine Closure (HPU); Participants allocated to this arm undergo primary cesarean section with single-layer uterine closure (hysterorrhaphy). After fetal and placental extraction, the uterine incision is closed in one single layer using a continuous absorbable suture (polyglactin 910 or equivalent), which approximates the myometrium in a running unlocked pattern. No second imbricating layer is performed. Additional interrupted sutures (reinforcement stitches) may be placed if necessary for bleeding control. All participants are followed postoperatively with standardized transvaginal ultrasound assessments at 6 weeks and 6 months to evaluate residual myometrial thickness (RMT) and cesarean scar defect (niche) development, as well as clinical symptom monitoring.	Procedure: Single-layer hysterorrhaphy at primary cesarean section; After fetal and placental delivery, the uterine incision is closed in one single layer using a continuous absorbable suture (polyglactin 910) approximating the full myometrial thickness in a running pattern. No second reinforcement layer is performed. Additional reinforcement sutures are placed if needed. This represents the conventional standard technique for uterine closure at cesarean section.; Other Names: One-layer uterine closure; Single-layer uterine closure; HPU technique
Experimental: Double-layer Uterine Closure (HDP); articipants allocated to this arm undergo primary cesarean section with double-layer uterine closure (hysterorrhaphy). After fetal and placental extraction, the uterine incision is closed in two distinct layers using a continuous absorbable suture (polyglactin 910 or equivalent). The first layer approximates the myometrium with a running unlocked suture. The second layer invaginates the first using a continuous suture to reinforce the closure and improve hemostasis. Additional interrupted sutures (reinforcement stitches) may be placed if necessary for bleeding control. All participants are followed postoperatively with standardized transvaginal ultrasound assessments at 6 weeks and 6 months to evaluate residual myometrial thickness (RMT) and cesarean scar defect (niche) development, as well as clinical symptom monitoring.	Procedure: Double-layer hysterorrhaphy at primary cesarean section; After fetal and placental delivery, the uterine incision is closed in two layers using continuous absorbable suture (polyglactin 910). Layer 1: running suture approximating the full myometrial thickness. Layer 2: continuous imbricating suture reinforcing the first layer and improving hemostasis. Additional reinforcement sutures placed if needed. Aims to optimize uterine scar healing and reduce cesarean scar defect (niche) formation.; Other Names: Two-layer uterine closure; Double-layer uterine closure; HDP technique

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Residual Myometrial Thickness (RMT) at the Cesarean Scar at 6 Weeks and 6 Months	Residual myometrial thickness (RMT) measured in millimeters at the thinnest point of the uterine scar using standardized transvaginal two-dimensional ultrasound, performed by blinded sonographers according to the protocol of Naji et al. (2012). RMT compared between single-layer (HPU) and double-layer (HDP) closure groups at 6 weeks and 6 months postoperatively.	6 weeks and 6 months after cesarean section
Prevalence of Cesarean Scar Defect (Niche) at 6 Weeks and 6 Months Postoperatively	Cesarean scar defect (niche) defined as a hypoechoic triangular indentation at the site of the uterine incision with depth ≥ 2mm or residual myometrial thickness (RMT)/adjacent myometrial thickness (AMT) ratio < 50%, detected by standardized transvaginal two-dimensional ultrasound. Prevalence compared between single-layer (HPU) and double-layer (HDP) closure groups at 6 weeks and 6 months postoperatively.	6 weeks and 6 months after cesarean section

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Prevalence of Gynecological Symptoms Related to Cesarean Scar Defect	Assessment of symptoms potentially related to uterine scar defect including: postmenstrual spotting, menometrorrhagia, dysmenorrhea, chronic pelvic pain, dyspareunia, urinary symptoms, and abnormal uterine bleeding at day 10 postoperatively. Symptoms assessed by standardized clinical questionnaire at 6 weeks and 6 months. Compared between HPU and HDP groups.	Day 10, 6 weeks, and 6 months after cesarean section
Identification of Independent Risk Factors for Cesarean Scar Defect Formation	Identification of independent risk factors for cesarean scar defect (niche) at 6 weeks and 6 months using multivariate logistic regression analysis. Variables assessed include: closure technique, operative duration, use of reinforcement sutures, uterine position, BMI, parity, type of cesarean section (elective vs emergency), and cervical dilation at time of surgery.	6 weeks and 6 months after cesarean section
Cesarean Scar Defect Linear Dimensions	Length, width, and depth of detected cesarean scar defect measured in millimeters by transvaginal ultrasound at 6 weeks and 6 months. Unit of Measure: Millimeters (mm)	6 weeks and 6 months after cesarean section
Cesarean Scar Defect Volume	Estimated volume of cesarean scar defect calculated using ellipsoid formula: V(mm³) = (π/6) × Length × Width × Depth Unit of Measure: Cubic millimeters (mm³)	6 weeks and 6 months post-cesarean
Operative Duration of Hysterorrhaphy and Total Cesarean Section	Measurement of time (minutes and seconds) required for uterine closure (hysterorrhaphy duration) and total operative time from skin incision to skin closure. Number of suture materials used and frequency of additional reinforcement sutures also recorded. Compared between HPU and HDP groups.	preoperative (during cesarean section procedure)
Intraoperative Complications Rate	Rate of intraoperative complications including hemorrhage requiring transfusion, bladder injury, ureteral injury, and unintended uterine incision extension. Unit of Measure: Number of events (n) and percentage (%)	Perioperative : During cesarean section procedure
Postoperative Infectious Complications Rate	Rate of postoperative infectious complications including endometritis, surgical site infection, and urinary tract infection, assessed during hospitalization and at 6-week visit. Unit of Measure: Number of events (n) and percentage (%)	Up to 6 weeks after cesarean section
Hospital Length of Stay	Number of days from cesarean section to hospital discharge. Unit of Measure: Days	Up to 5 days after cesarean section
Blood Transfusion Requirement	Number of packed red blood cell units transfused during hospitalization. Unit of Measure: Number of units	Up to 5 days after cesarean section

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Mediation Analysis: Role of Early Scar Defect in Late Outcome	Formal mediation analysis (Baron-Kenny approach, Sobel test, non-parametric bootstrap with 10,000 replications) to quantify the proportion of the protective effect of double-layer closure on 6-month niche prevalence that is mediated through prevention of early niche formation at 6 weeks. Proportion of mediated effect and direct/indirect effects will be calculated.	6 weeks and 6 months after cesarean section
Development of a Clinical Symptom-Based Predictive Score for Cesarean Scar Defect	Development and internal validation of a clinical predictive score based exclusively on self-reported symptoms (spotting, dysmenorrhea, pelvic pain, cycle irregularity) to identify patients at risk of cesarean scar defect at 6 months, without requiring ultrasound. Firth penalized logistic regression, 10-fold cross-validation, and bootstrap validation will be performed. AUC, sensitivity, specificity, PPV, NPV reported.	6 months after cesarean section
Identification of a Functional RMT Threshold Associated with Symptomatic Risk	Identification of a residual myometrial thickness (RMT) threshold at 6 weeks postoperatively that is associated with increased risk of gynecological symptoms at 6 months, using ROC curve analysis and dose-response gradient assessment. This threshold will complement existing obstetric safety thresholds by adding a functional/symptomatic dimension.	6 weeks and 6 months after cesarean section

Collaborators and Investigators

• Sponsor: Hédi Chaker Hospital
• Investigators: Principal Investigator: Derbel Mohamed, Professor, Department of obstetric and gynaecology of Hedi Chaker sfax; Principal Investigator: Khanfir Fatma, Professor, Department of obstetric and gynaecology of Hedi Chaker sfax

Publications and helpful links

General Publications

• Bij de Vaate AJ, van der Voet LF, Naji O, Witmer M, Veersema S, Brolmann HA, Bourne T, Huirne JA. Prevalence, potential risk factors for development and symptoms related to the presence of uterine niches following Cesarean section: systematic review. Ultrasound Obstet Gynecol. 2014 Apr;43(4):372-82. doi: 10.1002/uog.13199.
• Jordans IPM, de Leeuw RA, Stegwee SI, Amso NN, Barri-Soldevila PN, van den Bosch T, Bourne T, Brolmann HAM, Donnez O, Dueholm M, Hehenkamp WJK, Jastrow N, Jurkovic D, Mashiach R, Naji O, Streuli I, Timmerman D, van der Voet LF, Huirne JAF. Sonographic examination of uterine niche in non-pregnant women: a modified Delphi procedure. Ultrasound Obstet Gynecol. 2019 Jan;53(1):107-115. doi: 10.1002/uog.19049.
• Di Spiezio Sardo A, Saccone G, McCurdy R, Bujold E, Bifulco G, Berghella V. Risk of Cesarean scar defect following single- vs double-layer uterine closure: systematic review and meta-analysis of randomized controlled trials. Ultrasound Obstet Gynecol. 2017 Nov;50(5):578-583. doi: 10.1002/uog.17401. Epub 2017 Oct 9.
• Roberge S, Demers S, Berghella V, Chaillet N, Moore L, Bujold E. Impact of single- vs double-layer closure on adverse outcomes and uterine scar defect: a systematic review and metaanalysis. Am J Obstet Gynecol. 2014 Nov;211(5):453-60. doi: 10.1016/j.ajog.2014.06.014. Epub 2014 Jun 6.
• Stegwee SI, Ben AJ, El Alili M, van der Voet LF, de Groot CJM, Bosmans JE, Huirne JAF; 2Close study group. Cost-effectiveness of single-layer versus double-layer uterine closure during caesarean section on postmenstrual spotting: economic evaluation alongside a randomised controlled trial. BMJ Open. 2021 Jul 2;11(7):e044340. doi: 10.1136/bmjopen-2020-044340.

Helpful Links

• Jordan et al. 2019 - European Niche Task Force consensus on sonographic examination of uterine : nicheSonographic examination of uterine niche in non-pregnant women: a modified Delphi procedure

Study record dates

Study Major Dates

• Study Start (Actual): January 1, 2025
• Primary Completion (Actual): January 1, 2026
• Study Completion (Actual): April 30, 2026

Study Registration Dates

• First Submitted: May 9, 2026
• First Submitted That Met QC Criteria: May 20, 2026
• First Posted (Actual): May 28, 2026

Study Record Updates

• Last Update Posted (Actual): May 28, 2026
• Last Update Submitted That Met QC Criteria: May 20, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Ultrasound; Cesarean; Scar healing; single layer; double layer; Residual Myometrial Thickness (RMT); Isthmocele-niche
• Additional Relevant MeSH Terms: Urogenital Diseases; Genital Diseases; Pain; Neurologic Manifestations; Pathologic Processes; Female Urogenital Diseases; Female Urogenital Diseases and Pregnancy Complications; Uterine Diseases; Genital Diseases, Female; Hemorrhage; Uterine Hemorrhage; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Pelvic Pain; Metrorrhagia
• Other Study ID Numbers: 31/26

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared publicly due to patient confidentiality requirements and institutional regulations. Aggregate results will be published in peer-reviewed journals.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No