Double Versus Single Cervical Cerclage in Women with Cervical Insufficiency: A Systematic Review of Prophylactic and Emergency Indications

Abstract

Background/Objectives: Cervical insufficiency remains a leading cause of second-trimester pregnancy loss and early preterm birth. Although single-level cerclage techniques such as McDonald or Shirodkar are widely accepted, the potential advantages of double or modified double-level cerclage remain controversial. Methods: This systematic review was conducted in accordance with PRISMA guidelines. Comprehensive searches of PubMed, Embase, Web of Science, and the Cochrane Library (to September 2025) were supplemented by Google Scholar and conference proceedings. Eligible studies included randomized controlled trials, comparative cohort studies, and case series directly comparing double versus single transvaginal cerclage. A total of twenty-six sources were included, spanning randomized trials, comparative cohort studies, published protocols, case series, systematic reviews, conference abstracts, and early technical or historical reports. The primary outcome was preterm birth before 34 weeks; secondary outcomes were GA at delivery, latency, neonatal morbidity and mortality, and maternal complications. Results: Across prophylactic (history- or ultrasound-indicated) settings, double sutures produced outcomes comparable to single-level cerclage without consistent superiority. In contrast, in emergency or exam-indicated cases with advanced cervical dilation or bulging membranes, double or double-level cerclage significantly prolonged latency and reduced very preterm birth (<32–34 weeks). Double-level reinforced techniques (including monofilament-based and modified Wurm-type approaches) showed improved mechanical support and lower neonatal intensive-care admission. Case series further demonstrated successful rescue procedures beyond 24 weeks, indicating expanded surgical feasibility in selected patients. Conclusions: While double cerclage yields similar results to single cerclage in prophylactic use, it appears advantageous in high-risk or emergency scenarios. Comparative analyses suggest that combined mechanical and infection-controlled approaches may improve cervical competence and prolong gestation in selected patients. Ongoing multicenter randomized trials are needed to establish its definitive role in modern obstetric practice.

1. Introduction

Cervical insufficiency remains a major contributor to second-trimester pregnancy loss and early preterm birth. Cervical cerclage, first described by Shirodkar [1] and McDonald [2], has long served as the cornerstone intervention for women at risk. Traditionally, a single purse-string suture is placed around the cervix to reinforce mechanical strength and prolong gestation.

In challenging clinical scenarios—particularly those involving advanced cervical dilation or bulging membranes—some clinicians have advocated the use of two sutures, the so-called double McDonald cerclage, to provide additional mechanical support. Variants such as the cross-double McDonald, double-level monofilament (modified Wurm type) technique, and sequential second emergency cerclage have also been reported.

The concept of double-level cervical cerclage was first formally described almost simultaneously in early clinical case series by Ogawa et al. [3] and Park et al. [4]. Ogawa and colleagues reported a modified double cerclage technique for advanced cervical changes, demonstrating clinical feasibility and favorable early outcomes. These foundational studies established the clinical basis for subsequent comparative investigations and later technical innovations, including the modified Wurm type modification and monofilament suture approaches.

Although conceptually appealing, the effectiveness and safety of double compared with single cerclage remain uncertain, particularly outside emergency indications. Previous studies on double cerclage were limited by small sample sizes, heterogeneous definitions, and a lack of prospective randomization. Most comparative data originate from history-indicated (HI) or ultrasound-indicated (UI) settings, where a definitive benefit has not been demonstrated. Conversely, emerging evidence suggests potential advantages in emergency cases with advanced cervical changes or among women with a very short cervix.

This review aims to systematically synthesize the available evidence on double McDonald cerclage and related techniques, comparing maternal and neonatal outcomes with those of single cerclage across different clinical indications (HI, UI, and emergency/ECC) and pregnancy types (singleton and twin gestations). To the best of our knowledge, this is the first systematic review to directly compare single versus double suture techniques for transvaginal cervical cerclage in both prophylactic and emergency contexts.

2. Materials and Methods

2.1. Protocol and Registration

This systematic review was performed in accordance with the PRISMA 2020 guidelines, ensuring methodological transparency and reproducibility. Although the protocol was not prospectively registered in PROSPERO or any other registry, the review followed a predefined internal plan specifying objectives, eligibility criteria, databases, and analytic procedures prior to literature screening. The exploratory nature of the review reflects its basis on previously published clinical studies without individual patient-level data, yet the methodological framework remained systematic and replicable.

The primary objective was to synthesize and critically appraise existing evidence comparing single- versus double-level cervical cerclage techniques in women at risk for cervical insufficiency.

2.2. Eligibility Criteria

Studies were eligible for inclusion if they enrolled pregnant women with or at high risk for cervical insufficiency and provided a direct comparison between double-level (e.g., double McDonald, two-stitch, cross-double, modified Wurm, second emergent double, or cervical occlusion) and single-level (McDonald or Shirodkar) cerclage techniques.

The primary outcome was the incidence of preterm birth (<34 weeks of gestation). Secondary outcomes included gestational age (GA) at delivery, latency period, neonatal survival, neonatal intensive care unit (NICU) admission, and maternal surgical or infectious complications.

Eligible study designs comprised randomized controlled trials (RCTs), prospective and retrospective comparative cohort studies, and case series with ≥10 participants. Exclusion criteria were animal or in vitro studies, non-comparative reviews, editorials, letters, conference abstracts without outcome data, and duplicated datasets.

2.3. Information Sources and Search Strategy

A comprehensive literature search was conducted across PubMed, Embase, Cochrane Library, and Web of Science, supplemented by Google Scholar to capture grey literature, conference proceedings, and potentially unpublished studies.

The following Boolean combinations were used: (“cervical insufficiency” OR “incompetent cervix”) AND (“cerclage” OR “suture” OR “McDonald” OR “Shirodkar” OR “double” OR “two-stitch” OR “Wurm” OR “cross-double” OR “cervical occlusion”).

No language or regional restrictions were applied.

The search covered studies published from database inception through 30 September 2025, with reference lists of included papers and prior reviews manually screened for additional eligible studies.

All retrieved records were imported into EndNote 20 (Clarivate Analytics) for reference management, and duplicate entries were removed using automated and manual filters.

2.4. Study Selection

Two reviewers independently screened all retrieved titles, abstracts, and full texts against the predefined eligibility criteria.

A total of 260 records were identified through database searches and manual reference checks. After removal of 168 duplicates, 92 unique records remained for screening; 66 were excluded based on title or abstract review. The remaining 26 studies met the inclusion criteria and were incorporated into the final qualitative synthesis.

Common exclusion reasons included non-comparative design, absence of outcome data, or overlapping cohorts. Any discrepancies were resolved through discussion and consensus. The overall selection process, including numbers at each stage and reasons for exclusion, is illustrated in Figure 1, in accordance with PRISMA 2020 standards.

2.5. Data Extraction and Management

Two reviewers independently extracted data using a standardized template that captured study design, sample size, clinical indication (HI, UI, ECC), gestational outcomes, suture type/configuration, and maternal–neonatal outcomes. When multiple publications involved overlapping cohorts, the most comprehensive or recent dataset was retained to avoid duplication.

2.6. Risk of Bias and Quality Assessment

The methodological quality and risk of bias of the included studies were assessed using validated tools according to study design. For randomized controlled trials, the Cochrane Risk of Bias 2.0 tool was applied, evaluating randomization, allocation concealment, blinding, incomplete outcome data, selective reporting, and other potential sources of bias. For non-randomized studies, including retrospective and prospective cohort studies, the Newcastle–Ottawa Scale (NOS) was used to assess selection, comparability, and outcome domains. Case series were narratively appraised for methodological rigor, reporting quality, and completeness of outcome data. A summary of the quality assessment for each study is presented in

Table 1. Comparative Studies of Double- vs. Single-Level Cervical Cerclage.

Study (Year)	Design	Indication	Intervention (N)	Primary Outcome	Main Result/ Conclusion	Quality Tool	Risk of Bias
Choi et al. (2003) [5]	Retrospective cohort	Reoperation after failed TVC	Double MTVC n = 28 vs. TAC n = 13 (N = 41)	Fetal salvage, GA at delivery	Fetal salvage: 85.7% (24/28) vs. 100% (13/13), NS; less invasive than TAC.	NOS	6/9 (moderate)
Lee et al. (2004) [6]	Retrospective cohort	HI/UI	Double MTVC n = 44 vs. Single TVC n = 94 (N = 138)	PTB < 34 wk, GA	≥34 wk: 90.9% (40/44) vs. 74.0% (70/94), p < 0.05; pregnancy prolongation 21.5 vs. 19.5 wk, p = 0.013 (favors double).	NOS	8/9 (good)
Woensdregt et al. (2008) [7]	Retrospective cohort	HI/UI	Double n = 38 vs. Single n = 112 (N = 150)	GA at delivery; PTB < 37, <34, <28 weeks	Median GA 38.3 vs. 38.0 wk, NS; PTB < 34 wk: 18.4% (7/38) vs. 16.8% (19/112), NS; PTB < 28 wk: 2.6% (1/38) vs. 9.4% (10/112), NS → no measurable benefit of double.	NOS	6/9 (moderate)
Tsai et al. (2009) [8]	Randomized trial	HI: ≥1 prior 2nd-trimester loss	Double n = 17 vs. Single n = 34 (N = 51)	GA at delivery, PTB < 28/<34 wk, birthweight	GA 35.9 vs. 32.9 wk (p = 0.045); PTB < 28 wk 5.9% (1/17) vs. 29.4% (10/34), NS; PTB < 34 wk 23.5% (4/17) vs. 38.2% (13/34), NS; higher birthweight and better Apgar with double; neonatal survival similar.	RoB 2.0	Low risk
Broumand et al. (2011) [9]	Randomized trial	HI/UI with CL < 25 mm	Double (TVC + cervical occlusion) n = 28 vs. Single (TVC only) n = 28 (N = 56)	PTB < 33 wk	PTB < 3 3 wk: 0% (0/28) vs. 18% (5/28), p < 0.05; GA 37.4 vs. 36.2 wk, NS; higher 5-min Apgar and better neonatal outcomes with double.	RoB 2.0	Low risk
Park JM et al. (2012) [10]	Retrospective cohort	HI/UI/ECC mixed	Double n = 63 vs. Single n = 83 (N = 146)	PTB < 35 wk, GA at delivery	PTB < 35 wk: 30/63 (47.6%) vs. 34/83 (41.0%), p = 0.63; higher cerclage height with two stitches (20 vs. 17 mm) without outcome benefit.	NOS	7/9 (good)
Giraldo-Isaza et al. (2013) [11]	Retrospective cohort	HI/UI	HI: Double 86 vs. Single 151 (N = 237) UI: Double 117 vs. Single 90 (N = 207)	PTB < 37 wk (both HI & UI)	HI: PTB < 37 wk 35% (30/86) vs. 39% (59/151), NS; no differences at <35–<24 wk UI: PTB < 37 wk 44% (51/117) vs. 49% (44/90), NS; fewer very early PTB < 28 wk (11% vs. 24%) and <24 wk (5% vs. 14%) with double, but underpowered.	NOS	7/9 (good)
Zolghadri et al. (2014) [10]	Randomized trial	HI + recurrent mid-trimester loss	Double n = 19 vs. Single n = 14 (N = 33)	GA at delivery; PTB < 34 weeks	PTB < 34 wk: 10.5% (2/19) vs. 35.7% (5/14), p = 0.106; GA 37.2 ± 2.6 vs. 34.3 ± 3.8 wk (p = 0.016) → later delivery with double; other outcomes similar.	RoB 2.0	Low risk
Xu Z-M et al. (2023) [12]	Retrospective cohort	ECC (singletons)	Double n = 13 vs. Single n = 13 (N = 26)	GA at delivery; PTB < 34/<32 weeks	GA 32.7 ± 5.5 vs. 28.0 ± 4.7 wk (p = 0.028); PTB < 32 wk: 38.5% (5/13) vs. 92.3% (12/13), p = 0.013; PTB < 34 wk: 46.2% (6/13) vs. 92.3% (12/13), p = 0.034 → double associated with later GA and lower early PTB; NICU admission and LOS significantly lower with double.	NOS	7/9 (good)
Qiu et al. (2024) [13]	Retrospective matched cohort	ECC (twins)	Double n = 42 vs. Single n = 42 (N = 84)	GA at delivery; latency; spontaneous PTB < 28/<30/<32/<34 wk	GA 30.5 vs. 27.0 wk (p < 0.001); Pregnancy latency 56 vs. 28 days (p < 0.001); Spontaneous PTB < 28 wk 16.7% vs. 57.1% (p = 0.001); PTB < 30 wk 38.1% vs. 76.8% (p = 0.001); Higher birthweight (1544 vs. 980 g, p < 0.001); Perinatal mortality 7.1% vs. 31% (p = 0.014).	NOS	7/9 (good)
Donadono et al. (2025) [14]	Prospective multicenter cohort	HI/UI, CL ≤ 25 mm	Double (modified Wurm) n = 112 vs. Single n = 118 (N = 230)	PTB < 32 weeks (overall and CL ≤ 25 mm subgroup)	Overall: PTB < 32 wk 13% (7/55) vs. 24% (22/92), p = 0.169, NS; CL ≤ 25 mm subgroup: PTB < 32 wk 9% (3/35) vs. 29% (14/48), p = 0.042 → significant benefit with modified Wurm double cerclage in markedly short cervix.	NOS	9/9 (excellent)
Xu ZM et al. (2025) [15]	Stratified randomized trial	UI/ECC	UI: Double 23 vs. Single 25 (N = 48) ECC: Double 25 vs. Single 25 (N = 50)	PTB < 34 wk (primary); PTB < 28 wk (ECC subgroup)	UI: PTB < 34 wk 8.7% (2/23) vs. 0% (0/25), p = 0.224 → no clear difference; ECC: PTB < 34 wk NS, but PTB < 28 wk reduced with double (12% vs. 40%, p = 0.024).	RoB 2.0	Low risk

Abbreviations: HI = history-indicated; UI = ultrasound-indicated; ECC = emergency cervical cerclage; GA = gestational age; PTB = preterm birth; CL = cervical length; TVC = transvaginal cerclage; TAC = transabdominal cerclage; MTVC = modified transvaginal cerclage; NICU = neonatal intensive care unit; LOS = length of stay; NS = not significant; NOS = Newcastle–Ottawa Scale; RoB 2.0 = Revised Cochrane Risk of Bias Tool; Wurm = modified double-level monofilament cerclage technique.

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2.7. Synthesis of Results

Data were synthesized according to clinical indication and cerclage type (single vs. double; modified vs. standard). Where available, summary measures such as odds ratios (ORs) and mean differences (MDs) with corresponding 95% confidence intervals (CIs) were extracted or calculated. Visual summaries, including forest plots and heatmaps, were generated to illustrate comparative outcome trends across study designs and indications.

Because of substantial clinical and methodological heterogeneity—including differences in study design, indication, surgical technique, and outcome definitions—a formal meta-analysis was not feasible. Therefore, results were summarized qualitatively, emphasizing directional trends rather than pooled effect estimates. A formal meta-analytic synthesis is planned for future work once standardized datasets and uniform reporting criteria become available.

2.8. Limitations

This review has several limitations. Marked clinical and methodological heterogeneity among the included studies precluded formal meta-analysis. Most studies were retrospective and single-center, often lacking standardization of the “double cerclage” technique, suture material, and procedural details. Randomized evidence remains limited, and small sample sizes may have increased the risk of type II error.

Potential publication and language bias cannot be excluded because several early reports were published in non-English journals and may not have been indexed in major databases. Inconsistent definitions of key outcomes (e.g., latency, neonatal morbidity) further restricted quantitative comparison.

Despite these limitations, this review provides the most comprehensive and updated synthesis of double- versus single-level cervical cerclage to date, integrating historical experience with emerging evidence across diverse clinical indications.

Although the review followed PRISMA 2020 methodological standards, the protocol was not prospectively registered in PROSPERO or any other public registry. This constitutes a methodological limitation because the absence of prior registration may introduce risks of selective reporting and reduced transparency in analytic decisions. The primary reason for non-registration was that the review was initially developed as an exploratory synthesis integrating heterogeneous comparative studies, early technical case series, and evolving hybrid cerclage approaches that did not align with the rigid format required for PROSPERO registration. Nevertheless, all eligibility criteria, search strategies, and analytic procedures were predefined before literature screening, and the review was conducted in accordance with PRISMA principles to minimize potential bias.

3. Results

3.1. Study Selection and Characteristics

The overall study selection process is presented in Figure 1 (PRISMA Flow Diagram). A total of 260 records were identified through database and manual searches. After removal of duplicates, 92 unique records remained. Following title, abstract, and full-text screening, 26 studies met the inclusion criteria for this systematic review.

These Comprised:

• 6 Randomized Controlled Trials or Randomized Abstract Studies
• 6 Comparative Cohort or Matched Case–control Studies
• 3 Published Study Protocols for Ongoing or Completed Randomized Trials (including the CERVO protocol and its corresponding completed RCT outcome report)
• 4 Case Series or Single Case Reports
• 3 Systematic Reviews or Meta-Analyses
• 2 Conference Abstracts
• 2 Historical or Early Technical Descriptions (Including the Foundational Reports From 1987 and 1999)

Details of the 12 comparative studies included in the quantitative or qualitative evaluation of single versus double cerclage are presented in Table 1, accompanied by methodological quality and risk-of-bias assessments. Foundational non-comparative reports are summarized in Supplementary Table S1.

3.2. Early Evidence

The earliest conceptualization of double-level cervical cerclage can be traced to Hochuli and Vogt (1987) [16], who introduced the term “Doppelcerclage” for managing mid-trimester cervical insufficiency with membrane prolapse, demonstrating its technical feasibility. Ogawa et al. (1999) [3] later presented the first structured case series (n = 5) using a systematic two-level reinforcement in advanced dilation, followed by Park et al. (2000) [4], who described a modified transvaginal double McDonald cerclage reinforced with fibrin sealant.

These near-simultaneous Japanese and Korean reports marked the initial organized efforts to validate the double-cerclage concept, establishing its clinical feasibility and conceptual basis for subsequent comparative and technical innovations such as the modified Wurm-type double-monofilament technique.

3.3. Indications

Among the included studies, four primarily addressed history- or ultrasound-indicated (HI/UI) cerclage [7,10,11,17], whereas another four focused on ECC cases [13,14,16]. Two investigations specifically evaluated modified double-level or modified Wurm-type techniques [15,18].

Together, these studies represent the full spectrum of cervical insufficiency—from prophylactic to emergency presentations—enabling context-specific comparison of double versus single suturing under varying degrees of cervical compromise.

This classification was adopted throughout the analysis to ensure that outcomes were interpreted within each indication subgroup, rather than pooled across heterogeneous conditions.

3.4. Populations

Across the included studies, sample sizes varied widely—from small case series of 1–15 patients [3,4,18,19] to comparative cohorts enrolling up to 150 participants [7]. Most randomized and retrospective investigations [10,17,19] focused on singleton pregnancies with history- or ultrasound-indicated risk factors.

In contrast, several emergency or high-risk cohorts—most notably Qiu et al. [13] involving twin gestations with membrane prolapse—expanded the population spectrum beyond singleton cases. Overall, the analyzed populations represent the full range of clinical presentations—from prophylactic to emergent cerclage—highlighting that study outcomes reflect both anatomical and indication-specific differences rather than sample-size effects alone.

3.5. Designs

The body of evidence primarily comprised retrospective comparative cohort studies, supplemented by randomized controlled trials (including preprints and congress abstracts), along with an ongoing prospective multicenter protocol such as the COSA trial (Kosińska-Kaczyńska et al., Denmark) [20]. In addition, the CERVO program (Europe) encompasses both a published trial protocol by Secher et al. [19] and a completed randomized controlled trial by Brix et al. [21] evaluating cerclage with and without cervical occlusion. Complementing these clinical evaluations, Noori et al. [22] provided a foundational conceptual review outlining the rationale, theoretical mechanisms, and early observational experience underlying cervical occlusion as an adjunct to standard cerclage.

In addition, multiple case reports and technical notes contributed to understanding the procedural evolution of double- or multi-level suturing.

Overall, these investigations illustrate the chronological and methodological progression of the double-cerclage literature—from early conceptual reports to contemporary randomized designs—clarifying that evidence has shifted from descriptive feasibility toward structured clinical comparison.

3.6. Outcomes in HI and UI Cerclage

In HI or UI contexts, most comparative studies have evaluated whether double-level suturing confers measurable benefit over a single McDonald or Shirodkar cerclage.

Lee et al. [6] (n = 138) compared standard TVC with a modified double-level technique (MTVC) reinforced by fibrin sealant. The modified approach achieved greater pregnancy prolongation (21.5 vs. 19.5 weeks, p = 0.013) and a higher rate of delivery ≥ 34 weeks (90.9% vs. 74.0%). Conversely, Woensdregt et al. [7] (n = 150) observed no significant difference in preterm birth < 34 weeks (18.4% vs. 16.8%) or median GA at delivery (38.3 vs. 38.0 weeks). Similarly, Park JM et al. [17] reported higher stitch placement with two sutures but no improvement in outcomes.

Among randomized or quasi-randomized studies, Tsai et al. [8] (RCT, n = 51) reported that double cerclage resulted in later gestational age at delivery (35.9 vs. 32.9 weeks, p = 0.045) and lower rates of PTB < 28 weeks (5.9% vs. 29.4%, NS) and PTB < 34 weeks (23.5% vs. 38.2%, NS), together with higher birthweight and better Apgar scores, in women with at least one prior second-trimester loss. Similarly, Broumand et al. [9] (RCT, n = 56) demonstrated fewer very preterm births (PTB < 33 weeks: 0% vs. 18%) and higher 5 min Apgar scores in the double-stitch group. In contrast, Zolghadri et al. [10] (RCT, n = 33) showed later gestational age at delivery with double cerclage (37.2 ± 2.6 vs. 34.3 ± 3.8 weeks, p = 0.016), although PTB < 34 weeks rates did not differ significantly (10.5% vs. 35.7%, p = 0.106).

Retrospective analyses yielded similarly mixed findings: Giraldo-Isaza et al. [11] reported no overall improvement in PTB < 37 weeks but suggested a possible reduction in very early preterm birth among UI cases. A meta-analysis by Pergialiotis et al. [23] (2015; ~880 women) indicated that double cerclage significantly reduced PTB risk < 34 weeks (OR 0.59, 95% CI 0.40–0.86) and <28 weeks (OR 0.43, 95% CI 0.26–0.73), although emergency indications were under-represented.

More recently, Damalie et al. [18] described successful term delivery after double cerclage in a woman with recurrent second-trimester losses.

Overall, evidence from HI and UI cohorts suggests that double cerclage provides comparable efficacy to single suturing, with occasional improvement in latency or very-early-PTB prevention but without consistent superiority across outcomes.

Synthesis: Across HI and UI settings, double cerclage did not consistently reduce preterm birth rates or improve neonatal outcomes compared with single sutures. However, several small randomized studies suggested potential benefit in women with prior second-trimester pregnancy loss, underscoring the need for adequately powered, high-quality randomized trials to clarify these findings.

3.7. Outcomes in Emergency Cerclage (ECC)

Recent comparative studies, particularly the work by Xu Z-M et al. [12], have demonstrated a measurable clinical advantage of double over single sutures in emergency cerclage. These data consistently show later gestational age at delivery, reduced rates of very preterm birth, and improved neonatal outcomes, without additional maternal morbidity or procedural risk.

More recently, a stratified randomized trial by Xu ZM et al. [15] corroborated these findings, showing that in emergency settings, double cerclage markedly reduced extreme preterm birth (<28 weeks: 12% vs. 40%, p = 0.024) and prolonged gestational latency. This trial currently provides the strongest prospective evidence supporting a context-dependent benefit of double cerclage in advanced cervical dilation or membrane prolapse.

Synthesis: The above studies—including the retrospective emergency cerclage analysis by Xu Z-M et al. [12] and the stratified randomized preprint by Xu ZM et al. [15]—represent a limited but important body of direct comparative evidence suggesting a measurable benefit of double cerclage in emergency settings.

In summary, these findings highlight a promising but still preliminary evidence base and underscore the urgent need for larger, multicenter prospective trials to validate and generalize these results.

Additional Evidence: Complementary evidence comes from Gnanarathne and Rathnayake [24], who reported a case series of five emergency cerclage procedures. Among these, three women with bulging membranes at 17–25 weeks’ gestation underwent double McDonald cerclage using nylon sutures. Notably, one patient required re-cerclage due to postoperative membrane descent, yet all three double-cerclage cases ultimately resulted in live births, with latency periods extending up to 143 days. Although limited in scale, these real-world data further support the technical feasibility and potential fetus-preserving impact of double cerclage, even at pre-viable or near-viable gestational stages.

3.8. Outcomes in Emergency Cerclage (ECC) of Twin Pregnancies

Qiu et al. [13] retrospectively compared a combined McDonald–Shirodkar approach—functioning as a practical double-level cerclage—with the conventional McDonald technique in 84 twin pregnancies requiring emergency cerclage between 18 and 26 weeks’ gestation (cervical dilation 1–6 cm). By including cases beyond the traditional 24-week cutoff originally applied to singleton gestations, this study expanded the clinical applicability of cerclage to high-risk twin pregnancies.

The double-level approach was associated with significantly longer latency (median 56 vs. 28 days), higher GA at delivery (30.5 vs. 27.0 weeks), and lower rates of very preterm birth and perinatal mortality, particularly among women presenting with ≥3 cm cervical dilation. These results reinforce growing evidence that an additional suturing layer can provide enhanced mechanical reinforcement in cases of advanced cervical dilation or membrane prolapse, suggesting a potential clinical advantage of double cerclage in both singleton and twin emergency contexts.

3.9. Modified Double-Level Techniques

Donadono et al. [14] (n = 147) conducted a comparative cohort study evaluating a modified Wurm type double-level cerclage using monofilament sutures versus a conventional McDonald cerclage performed with braided material. Among women with a cervical length (CL) ≤ 25 mm, preterm birth before 32 weeks was significantly reduced in the modified Wurm type group (9% vs. 29%; adjusted OR 0.25, 95% CI 0.06–0.95). Across the entire cohort, rates of preterm birth < 32 weeks and composite neonatal morbidity trended lower in the modified group, although statistical significance was not reached, and no increases in maternal or surgical complications were observed. These results suggest that the modified Wurm type approach may confer distinct benefit, particularly among women with a markedly short cervix.

Complementary preliminary data from Banerjee et al. [25] likewise indicate favorable outcomes with the double-monofilament technique in high-risk singleton pregnancies, although complete results remain unpublished.

Synthesis: Double-level and monofilament-based modifications appear clinically promising, especially for women with pronounced cervical shortening. Nevertheless, confirmation through adequately powered, prospective randomized trials remains essential to establish their definitive efficacy and safety.

3.10. Case Reports and Technical Variations

Case reports have documented a wide range of technical adaptations in double or multi-level cerclage procedures. These include cross-double McDonald cerclage used for hemostatic control, sequential second double McDonald cerclage performed after failure of the initial procedure, and hybrid double McDonald–Shirodkar techniques, even in twin gestations. Altogether, these reports underscore both the procedural versatility and the lack of universal standardization in double cerclage methods currently employed across institutions.

Early detailed descriptions of double-level cerclage also emerged from Korea. Park et al. [4] reported a case series of 15 women treated with a modified McDonald technique reinforced with fibrin sealant, Beriplast (CSL Behring GmbH, Marburg, Germany) This approach involved the placement of two sutures at different cervical levels with sealant injection between them and achieved an 87% neonatal survival rate even among high-risk women presenting with bulging membranes. This study represents one of the earliest systematic clinical experiences demonstrating the feasibility and potential benefit of double-level cerclage in challenging obstetric scenarios.

Building upon this foundation, Choi et al. [5] and Lee et al. [6]—both employing the same modified double-level technique originally introduced by Park et al. [4] —further expanded its clinical application. Choi et al. [5] compared modified transvaginal cerclage (MTVC) with transabdominal cervicoisthmic cerclage (TAC) in women with prior failed single cerclage and found comparable pregnancy prolongation and live-birth outcomes. Given that TAC requires laparotomy or laparoscopy and mandates cesarean delivery, the authors concluded that repeat double TVC could serve as a practical, less invasive alternative for selected high-risk patients.

Lee et al. [6] likewise demonstrated favorable outcomes with the modified double-level technique compared with the conventional single McDonald approach, consistent with earlier Korean experience.

Together, these three studies delineate the evolution of the early Korean double-level cerclage technique, which laid an important foundation for subsequent international adaptations of double-level cerclage.

3.11. Overall Synthesis

Across the available evidence, double cerclage has not demonstrated consistent superiority over a single stitch in HI/UI settings. Most randomized and cohort studies report comparable rates of preterm birth and neonatal outcomes, although the small randomized trial by Tsai et al. [8] suggested potential benefit among women with a history of second-trimester pregnancy loss, emphasizing the need for larger, high-quality trials.

In contrast, emergency cerclage (ECC) data indicate that double suturing may confer meaningful advantages, including longer gestational latency and reduced rates of very preterm birth. These findings are supported by the recent series from Park and Park [26], which analyzed 25 women referred after failed initial cerclage with bulging membranes. Following amnioreduction, removal of the prior suture, and placement of a second emergent double McDonald cerclage, 75% (20/25) of patients delivered beyond 29 weeks. This represents one of the largest systematic reports of “second emergent double McDonald cerclage” and demonstrates both technical feasibility and unexpectedly favorable outcomes, particularly when reoperation occurred after 24 weeks’ gestation.

Evidence from modified double-level or monofilament-based techniques—such as the modified Wurm type approach—suggests possible additional benefit among women with a markedly short cervix, without increasing maternal complications. Nevertheless, these promising trends require confirmation in future randomized studies.

Finally, case reports and technical notes—including those by Park et al. [4], Choi et al. [5] and Lee et al. [6]—illustrate the procedural evolution and adaptability of double-level cerclage but remain limited by small sample sizes and methodological heterogeneity. Earlier commentary by Namouz et al. [27] listed double cerclage among several technical modifications for emergency procedures (e.g., amnioreduction, balloon replacement of membranes, and modified Shirodkar), highlighting that at that time, the technique was largely anecdotal and lacked standardized definitions. Taken together, current evidence supports the feasibility and potential clinical value of double cerclage in selected high-risk or emergent scenarios while underscoring the pressing need for standardized surgical classification and prospective multicenter validation.

3.12. Quantitative Overview

A forest-style plot (Figure 2) was constructed to visually summarize the individual effect estimates from seven eligible comparative studies. Because of substantial heterogeneity in endpoints, populations, and study designs, no meta-analysis or pooled estimate was performed. The figure therefore serves solely as a descriptive comparison, illustrating the direction and variability of effect estimates across studies.

4. Discussion

Overview:

Evidence from this systematic review indicates that the clinical utility of double cervical cerclage is highly context-dependent. While prophylactic indications—those based on obstetric history or ultrasound-screening criteria—generally demonstrate neutral outcomes when comparing double versus single cerclage, emerging evidence from emergency cerclage (ECC) and modified double-level or monofilament techniques suggests a potential advantage in selected high-risk populations.

Taken together, these findings highlight the importance of individualized patient selection and procedural tailoring rather than uniform adoption of double suturing. The evolving evidence base supports the notion that the benefit of an additional suture may depend on the extent of cervical dilation, integrity of the remaining cervical tissue, and the timing of intervention.

In addition, apparent inconsistencies among studies likely reflect differences in operator decision-making, patient selection, and procedural refinement rather than true contradiction in clinical efficacy.

4.1. HI and UI Cerclage

Across major comparative studies—Woensdregt et al. [7], Park JM et al. [17], and Giraldo-Isaza et al. [11]—no consistent reduction in preterm birth (PTB) rates was observed with double versus single stitches.

• Woensdregt et al. [7] reported similar PTB < 34 weeks (18.4% vs. 16.8%) and comparable median GA (38.3 vs. 38.0 weeks).
• Park JM et al. [17] noted that two stitches allowed higher suture placement but did not improve outcomes.
• Giraldo-Isaza et al. [11] likewise found no overall benefit, though they observed a non-significant trend toward fewer very early PTBs (<28 and <24 weeks) in UI cases managed with double cerclage—suggesting that additional mechanical reinforcement may be advantageous in women with pronounced cervical shortening or funneling, a finding echoed later by Xu ZM et al. [15].

All three studies shared methodological limitations, including retrospective, surgeon-dependent design; modest sample sizes; heterogeneous techniques; exclusion of advanced/emergency cases; and lack of standardization in procedural variables such as suture height and material. Giraldo-Isaza et al. [11] also pooled heterogeneous indications without stratification, potentially masking subgroup effects. Consequently, while these studies established the safety and technical feasibility of double cerclage, their ability to demonstrate efficacy was limited.

Smaller randomized and observational investigations have hinted at potential benefit in selected high-risk subgroups.

• Broumand et al. [9] reported improved rates of viable extreme preterm birth and more favorable early neonatal outcomes with double cerclage compared with traditional cerclage, although interpretation is limited by small sample size, heterogeneous techniques, and the atypical use of an occlusive distal stitch.
• Zolghadri et al. [10] found later GA at delivery with double cerclage women with recurrent mid-trimester losses, although other outcomes did not differ significantly.
• Tsai et al. [8] (RCT) and Damalie et al. [18] (case report) similarly supported the feasibility of double cerclage in women with prior second-trimester loss or a markedly shortened cervix.
• Earlier Korean experience, particularly Lee et al. [6], also demonstrated improved pregnancy prolongation and reduced preterm delivery rates using a modified double-level technique reinforced with fibrin sealant, though results were limited to a single-center cohort.

Finally, the meta-analysis by Pergialiotis et al. [23], pooling more than 600 women (mostly HI/UI indications), found no significant reduction in PTB < 34 weeks or neonatal complications with double cerclage, reinforcing that routine prophylactic double cerclage offers no clear advantage. This lack of benefit has shifted recent research interest toward emergency and high-risk scenarios where additional suturing may be more mechanistically justified.

Synthesis: HI or UI cerclage has not demonstrated uniform superiority of double over single stitches in general populations. However, potential benefit may exist in carefully selected high-risk women—such as those with prior mid-trimester losses or severe cervical shortening—underscoring the need for future stratified and adequately powered randomized trials.

4.2. Emergency Cerclage (ECC)

Early clinical attempts to reinforce the cervix in cases of membrane prolapse date back to the late 1990s. Ogawa et al. [3] reported five emergency cases treated with a modified double-level cerclage after membrane reduction in the knee–chest position; two reached term and three neonates survived, establishing the principle of mechanical reinforcement for advanced cervical change. Almost contemporaneously, Park et al. [4] presented a 15-case Korean series of modified transvaginal double-level cerclage reinforced with fibrin sealant. Six of these involved emergency presentations with bulging membranes, while the remainder were prophylactic high-risk cases. Despite this heterogeneity, overall neonatal survival reached 87%, supporting the feasibility and potential benefit of the modified double-level approach. Together, these near-simultaneous reports from Japan and Korea provided the earliest structured clinical evidence for the double-level concept, bridging prophylactic and emergency contexts and laying the groundwork for modern double-suture techniques.

Evidence synthesis confirms that ECC is the most consistent context in which double cerclage confers measurable clinical benefit:

• Xu Z-M et al. [12]—Retrospective case–control study of singleton pregnancies with emergency indications: double cerclage achieved significantly longer GA at delivery (32.7 ± 5.5 vs. 28.0 ± 4.7 weeks, p = 0.028), lower PTB < 34 and <32 weeks, and reduced NICU admission and stay. Neonatal survival was comparable. The matched design under true emergency conditions minimized selection bias.
• Xu ZM et al. [15]—A stratified randomized controlled trial found no benefit in UI cases, but in emergencies, double cerclage markedly reduced extreme PTB < 28 weeks (12% vs. 40%, p = 0.024) and prolonged latency, providing the strongest prospective evidence of context-dependent benefit.
• Park and Park [28]—A series of 25 women referred after failed initial cerclage underwent removal of the prior suture and a second emergent double McDonald cerclage. Seventy-five percent delivered beyond 29 weeks—even when re-cerclage occurred after 24 weeks—challenging the traditional view that re-cerclage beyond 24 weeks is contraindicated.
• Qiu et al. [13]—Extended ECC indications to twin pregnancies (18–26 weeks) using a combined McDonald–Shirodkar (functionally double-level) technique. The double-level group achieved longer latency (56 vs. 28 days), higher GA (30.5 vs. 27.0 weeks), and reduced perinatal mortality, particularly with ≥3 cm dilation.

Recent randomized and observational data convergently reinforce that, although double cerclage shows no advantage for routine prophylaxis, it provides a clinically meaningful reduction in extreme preterm birth and improved latency in emergency settings.

Synthesis. Double cerclage appears most beneficial in cases of advanced cervical dilation, membrane prolapse, or multifetal gestation. The accumulating evidence suggests that the traditional “≤24-week limit,” originally derived from singleton-based protocols, may not be universally applicable.

To illustrate comparative outcomes, Figure 3 presents a heatmap summarizing gestational outcomes across major studies. As shown, absolute success rates are highest in HI and modified Wurm type cerclage, whereas emergency and twin pregnancies—though lower overall—still exhibit meaningful prolongation beyond 28 weeks.

4.3. Mechanistic Insights

Several mechanistic factors likely underlie the observed benefit of double cerclage in emergency settings.

• Mechanical reinforcement: Placement of two sutures distributes tension more evenly across the cervix, reducing the risk of suture cutting and maintaining a higher level of cervical closure. This configuration provides greater structural support, minimizing recurrent dilation or downward suture migration.
• Preservation of the mucus plug: Multiple authors (e.g., Namouz et al. [27]; Becher et al. [28]) have proposed that double cerclage more effectively preserves the integrity of the endocervical mucus plug, thereby maintaining local antimicrobial defense and decreasing the likelihood of ascending intrauterine infection.
• Barrier effect of sealant and occlusion: Korean studies [4,5,6] incorporating fibrin sealant reinforcement and cervical occlusion have reported additive protective effects, helping to prevent infection and premature rupture of membranes. Notably, the pioneering work of Baumgarten and Moser [29] demonstrated that fibrin adhesion applied to a modified single cerclage could prolong gestation by creating both a physical and biological barrier within the cervical canal. Subsequent Korean protocols advanced this principle by placing fibrin sealant between two separate sutures, thereby forming a multilayered barrier that not only reinforces mechanical closure but also preserves the integrity of the cervical mucus plug—an important component of local immune defense against ascending infection. This conceptual evolution represents a logical extension from single to double suturing, integrating both mechanical and biological protection.

4.4. Modified Double-Level Techniques

Modified approaches, particularly those employing monofilament materials such as the modified Wurm type double-level cerclage, represent an important evolutionary step in the refinement of cervical reinforcement strategies.

Donadono et al. [14] also demonstrated favorable outcomes with the modified Wurm double-level monofilament technique—particularly in women with a markedly short cervix—showing reduced early preterm birth compared with the conventional single McDonald approach, without added maternal morbidity.

• Banerjee et al. [25]: Preliminary data from high-risk singleton pregnancies suggested comparable trends favoring the modified Wurm type cerclage technique, although full peer-reviewed results remain unavailable.

It is noteworthy that, despite occasional references to a so-called “Wurm cerclage” in clinical discussions, only two modern works explicitly include the term “Wurm” in the article title—Banerjee et al. [25] and Donadono et al. [14]. This pattern suggests that the original “Wurm technique” functioned primarily as a regional Central-European surgical tradition rather than a formally published, standardized procedure, which may partly explain the lack of uniform terminology and technical definitions across the double-cerclage literature.

Synthesis. Double-level and monofilament-based modifications appear promising, particularly for women with a markedly short cervix, but the current supporting evidence is limited to non-randomized cohorts and preliminary reports. Prospective randomized trials will be essential to confirm these findings.

Historical note. The modern double-level concept originated from near-simultaneous East Asian reports and is summarized in the Historical Perspective (Phase 1) section.

4.5. Ongoing Trials and Future Directions

In addition to the accumulating retrospective evidence, one ongoing multicenter randomized protocol is expected to provide higher-level prospective data. The COSA trial (Denmark) [21] represents the first randomized, multicenter comparison of double-level versus single-level cerclage specifically in emergency indications, and its results are anticipated to clarify whether a two-level configuration confers measurable benefit in this context.

Separately, the CERVO program (Europe) has already completed its evaluation of adjunctive cervical occlusion: the initial protocol was published in 2007 by Secher et al. [19], and the subsequent randomized trial results were reported in 2013 by Brix et al. [21], representing the only completed RCT comparing cerclage with versus without an external cervical occlusion stitch. Brix et al. (2013) [21] found that cervical occlusion provided no significant benefit over routine cerclage; take-home baby rates were comparable in both the prophylactic (92% vs. 90%) and therapeutic (81% vs. 85%) strata, with no differences in gestational age at delivery, preterm birth <34 or <28 weeks, NICU admissions, or NICU stay. Insights from the ongoing COSA protocol and the completed CERVO trials are expected to refine the understanding of the optimal cerclage configuration and its context-specific value.

Overall, these trials will be critical for determining whether double-level cerclage or combined occlusive techniques should be integrated into routine clinical practice or reserved for selected high-risk populations. Their findings are expected to guide future international recommendations toward evidence-based procedural standardization.

However, despite being initiated years ago, progress has been slow. Recruitment and data reporting have been hampered by the rarity of eligible cases, the urgency and emotional distress surrounding emergency presentations, hesitancy toward randomization among both clinicians and patients, and the need for extended neurodevelopmental follow-up. Funding limitations and multicenter logistical barriers have further delayed completion. Consequently, accumulation of robust prospective evidence has progressed more slowly than anticipated, underscoring the continuing importance of high-quality registry data and coordinated international collaboration.

4.6. Synthesis and Interpretation of Findings

• Emergency settings:

Recent prospective and observational evidence consistently indicates that double cerclage provides clear clinical benefit in emergency situations, significantly prolonging gestation and reducing rates of very preterm birth—particularly in cases with membrane prolapse or advanced cervical dilation.

• Prophylactic (HI and UI) settings:

In contrast, prophylactic indications have not demonstrated consistent superiority of double over single cerclage. However, recent randomized data (e.g., Xu ZM et al. [15]) suggest potential benefit in selected high-risk subgroups—such as women with a history of second-trimester losses or marked cervical shortening—without an increase in adverse outcomes.

• Modified and adjunctive techniques:

Modified modalities, including double-level monofilament approaches and the use of adjunctive barriers such as fibrin sealant, appear promising for women with an extremely short cervix. Nonetheless, supporting evidence remains limited to preliminary or non-randomized data, underscoring the need for further validation.

• Historical context:

The conceptual foundation for modern double cerclage originates from near-simultaneous innovations by Ogawa et al. [3] and Park et al. [4]. The latter introduced the so-called “Candy Operation” which employed two transvaginal sutures reinforced with fibrin sealant—creating a configuration visually reminiscent of a wrapped candy. Subsequent Korean studies [5,6] expanded and refined this technique, exerting a lasting influence on the evolution of double-level cerclage methodology worldwide.

• Future research:

The only ongoing multicenter evaluation is the COSA trial (Denmark) [21], which is expected to clarify whether a double-level configuration provides measurable benefit in emergency indications. In contrast, the CERVO program (Europe) has already completed its assessment of adjunctive cervical occlusion: the initial protocol was published in 2007 by Secher et al. [19], and the subsequent randomized trial results were reported in 2013 by Brix et al. [21]. Future work should prioritize the standardization of procedural parameters—including suture type, knot orientation, and inter-suture spacing—and the generation of adequately powered, stratified evidence to determine when double cerclage confers a meaningful clinical advantage.

4.7. Clinical Implications and Limitations

Double cerclage is most consistently beneficial in emergency (exam-indicated) settings, where it prolongs gestation and reduces very preterm birth across retrospective and emerging prospective studies. In history- or ultrasound-indicated cases, routine use is not yet supported; however, the absence of major adverse outcomes and early signals of benefit suggest that it may be cautiously considered for select high-risk patients.

The biomechanical and barrier mechanisms underlying clinical success in emergency cerclage may, with further validation, also enhance outcomes for preventive indications. Until large randomized trials confirm safety and efficacy, individualized, risk-based case selection remains the most prudent approach.

Current evidence is limited by retrospective design, small sample size, and variable definitions of “double cerclage.” Inconsistent reporting of surgical details—such as knot position, cerclage height, and suture material—restricts reproducibility and meta-analytic synthesis. Twin gestations remain underrepresented, though small series suggest potential benefit in selected circumstances.

Our search strategy covered PubMed, Embase, Cochrane Library, and Web of Science, supplemented by Google Scholar to minimize publication bias. All results underwent manual screening and cross-checking to ensure methodological rigor and reproducibility in accordance with PRISMA 2020.

• Phase 1: Conceptual Foundation (1987–2007)

The conceptual origins of double cervical cerclage trace back to Germany, where Hochuli and Vogt [16] first proposed dual suturing for mid-trimester cervical insufficiency with prolapsed membranes. Although outcomes were not systematically reported, this pioneering work introduced the principle of enhanced mechanical reinforcement using two sutures—a concept that would later underpin modern double-level techniques.

A technical variant followed from Tsuji and Watanabe [30], who described a “double cervical cerclage with an auxiliary loop.” Their configuration combined a high-level Shirodkar suture with an adjunct loop for easier removal but did not involve two independent sutures at separate cervical levels; thus, it is better viewed as a hybrid modification rather than a true double-level cerclage.

Structured clinical adoption of double-level reinforcement began almost simultaneously in Japan and Korea at the turn of the millennium. Japanese and Korean teams around 1999–2000 reported structured case series demonstrating pregnancy prolongation—marking the first organized clinical application of dual mechanical support for cervical insufficiency.

A consecutive series of Korean investigations [4,5,6] led by the same corresponding author—further developed and refined the modified double-level TVC technique. The initial 2000 study introduced the double McDonald cerclage reinforced with fibrin sealant, achieving an 87% neonatal survival rate among high-risk pregnancies, including cases with bulging membranes. The subsequent 2003 study compared repeat transvaginal double cerclage with transabdominal cervico-isthmic cerclage after failed prior procedures, demonstrating comparable efficacy but reduced surgical morbidity, thus supporting the practicality of repeat vaginal cerclage. Finally, the 2004 study extended this double-level approach to HI and UI patients, showing prolonged gestation and higher term-delivery rates.

Phase 1 culminated in the publication of the CERVO protocol in 2007 (Secher et al. [19]), which provided the first structured framework for evaluating adjunctive cervical occlusion in a prospective manner. Noori et al. [22] further established the conceptual rationale by synthesizing the theoretical mechanisms and early clinical observations. Together, these developments set the stage for the subsequent clinical evaluation era.

• Phase 2: Transition and Reassessment (2008–2015)

Phase 2 began with the implementation and reporting of the CERVO randomized trial in 2013 (Brix et al. [21]), which demonstrated no significant benefit of adding cervical occlusion to routine cerclage; take-home baby rates, gestational age at delivery, preterm birth <34 or <28 weeks, and neonatal outcomes were comparable between the occlusion and non-occlusion groups. These randomized findings emerged against a background of earlier retrospective comparative studies in prophylactic HI/UI cohorts—most notably those by Woensdregt et al. [7], Park JM et al. [17], and Giraldo-Isaza et al. [11]—which likewise failed to show consistent advantages of double over single cervical cerclage. However, these investigations were predominantly retrospective, single-center, and surgeon-dependent, focusing mainly on HI/UI indications while excluding emergency cases, severe cervical shortening, or anatomically complex presentations. As a result, the accumulated evidence lacked the methodological rigor and clinical spectrum needed to support routine adoption of double suturing. The first systematic review by Pergialiotis et al. [23] synthesized this limited evidence base and similarly concluded that double cerclage did not significantly reduce preterm birth compared with single cerclage, reinforcing the notion that its potential value—if any—might lie not in broad prophylactic use but in more carefully selected high-risk populations.

• Phase 3: Evidence Refinement and International Expansion (2016–2025)

Over the past decade, renewed research attention has focused on emergency indications and the technical evolution of the double cerclage approach.

Gnanarathne and Rathnayake [24] further confirmed the feasibility and clinical value of double cerclage in three women with bulging membranes (17–25 weeks), each resulting in a live birth.

Building on these findings, Xu ZM et al. [15] conducted the first stratified randomized controlled trial, showing that double cerclage markedly reduced rates of extreme preterm birth (<28 weeks: 12% vs. 40%, p = 0.024) and prolonged gestational latency in the emergency subgroup.

Additional international evidence further reinforced these results. Park and Park [26] (conference abstract) reported successful second emergent double McDonald cerclage even after 24 weeks’ gestation, challenging long-standing timing limitations. Qiu et al. [13] demonstrated clear benefit in twin pregnancies up to 26 weeks, using a combined McDonald–Shirodkar (functionally double-level) technique. Donadono et al. [14] introduced the modified Wurm type cerclage method, reporting significantly reduced rates of preterm birth.

This broader shift toward individualized reinforcement strategies is further contextualized by the recent systematic review by Vaughan et al. [31], which evaluated 22 studies examining variations in cerclage technique, including Shirodkar versus McDonald and the addition of a second stitch. Although their primary objective was not to compare single versus double cerclage, the secondary analysis demonstrated that double suturing was associated with reduced pregnancy loss and lower rates of PTB < 28, <32, and <34 weeks, without differences at <37 weeks or in maternal complications. These findings, while methodologically distinct from the present review, provide complementary evidence suggesting that enhanced or multi-level reinforcement may offer selective benefit in women at highest risk of extreme or very early preterm birth.

In summary, current evidence suggests that the advantages of double cerclage arise not merely from suture duplication, but from superior anatomical coverage, preservation of the mucus barrier, and enhanced resistance against cervical stress and membrane prolapse. In summary, these findings mark the transition from experimental adaptation to systematic clinical validation, tracing an arc from the near-simultaneous conceptual innovations of Japan and Korea to broader international adoption. Emerging prospective data now support double or modified double-level cerclage as clinically viable options, warranting continued multicenter evaluation and long-term outcome surveillance.

• Phase 4—Future Directions: Technological and Clinical Frontiers (2025 → Beyond)

(1)

Next-Generation Technical Evolution

The future of double cerclage will emphasize procedural optimization and individualized application. Advances in suture materials—such as antibacterial coatings and integrated bio-sealants—may enhance both mechanical strength and infection resistance. Real-time, AI-assisted cervical imaging (including 3-dimensional ultrasound elasticity mapping and machine-learned models predicting suture tension and membrane stress) is expected to enable precision adjustment of suture height and knot positioning, evolving cerclage from a standardized to a personalized surgical intervention.

(2)

Large-Scale Evidence and Multicenter Trials

Ongoing randomized controlled trials, most notably the COSA study [21], are expected to clarify whether additional or modified double-level configurations can meaningfully reduce preterm birth and neonatal morbidity in emergency and high-risk settings.

Future international collaborations should incorporate adaptive RCT designs and network meta-analyses comparing single, double, and modified techniques across diverse indications—including HI, UI, and ECC cases, multifetal gestations, and short-cervix scenarios. Integration with large population registries such as the WHO Global Preterm Birth Initiative will allow real-world effectiveness to be assessed beyond specialized centers.

(3)

Data Harmonization and Registry-Driven Analytics

Establishing a Global Cervical Cerclage Registry collecting structured intra-operative metrics—suture type, placement, knot position, membrane status, and operator experience—would enable pooled machine-learning analytics to identify predictive factors for procedural success. Transitioning from fragmented single-center reports to registry-linked continuous quality-improvement frameworks could markedly accelerate evidence generation and guideline refinement.

(4)

Refined Indication Stratification

Future research must move beyond the homogeneous “cervical insufficiency” paradigm to distinguish biological and mechanical phenotypes: HI, UI, ECC, and multifetal pregnancies. Such stratification will clarify which patient subsets derive the greatest benefit from double-level reinforcement—particularly those with markedly short cervix, advanced funneling, or post-cerclage membrane prolapse.

(5)

Biomechanical and Infection-Immunologic Insights

Emerging innovations—including finite-element biomechanical modeling and ex vivo cervico-vaginal tissue studies—will elucidate how double-level suturing redistributes cervical stress and preserves mucus-plug function. Parallel investigations into the cervical microbiome and cytokine milieu may reveal whether double cerclage reduces ascending infection risk by maintaining canal integrity, potentially transforming the procedure from a purely mechanical to a hybrid biomechanical-immunologic intervention.

Figure 4 illustrates the chronological evolution of the double cervical cerclage technique, delineated into four major developmental phases.

Phase 1 (1987–2007) marks the conceptual foundation, during which early reports by Hochuli and Vogt [16], Ogawa et al. [3], and Park et al. [4] established the groundwork for modern double-level reinforcement.

Phase 2 (2008–2015) represents a period of transition and reassessment, characterized by comparative cohort analyses (Woensdregt et al. [7], Park JM et al. [17], Giraldo-Isaza et al. [11]) and the first meta-analysis (Pergialiotis et al. [23]), which questioned the universal benefit of the double-suture approach.

Phase 3 (2016–2025) reflects evidence refinement, highlighted by the emergence of emergency-focused and modified monofilament techniques (Xu et al. [12,15], Qiu et al. [13], Donadono et al. [14]) that demonstrated context-specific clinical advantages.

Phase 4 (2025 → Beyond) envisions future frontiers—featuring AI-guided imaging, bio-sealant sutures, and global multicenter registries that are expected to enable precision-guided, evidence-based adoption of double-level cerclage worldwide.

• Integrative Concluding Statement

Altogether, these future directions define the Phase 4 frontier of double-cerclage research—a transition from empirical adaptation to precision-based, evidence-driven surgical practice. The coming decade will be pivotal in determining whether double-level cerclage remains a specialized rescue intervention or evolves into a mainstream prophylactic strategy in modern obstetrics.

Future research—including ongoing randomized trials such as the COSA study [21]—is essential to clarify the true advantages of double-level over single cerclage. To advance the field, future studies should employ standardized definitions that distinguish true two-stitch approaches from auxiliary-loop modifications, transparently report suture type and placement, and stratify outcomes by indication, degree of cervical dilation, and singleton versus twin gestation. Large-scale international collaboration and registry-based prospective data collection will be crucial to achieve sufficient statistical power and global applicability.

At present, existing evidence does not demonstrate consistent superiority of double cerclage over single McDonald or Shirodkar techniques in prophylactic cases. Nevertheless, its comparable safety profile and equivalent perinatal outcomes justify its use as a reasonable alternative when adapted to surgeon expertise and patient-specific anatomy. In contrast, for emergency or high-risk scenarios, emerging randomized and observational data increasingly support double or modified double-level cerclage as a beneficial intervention. Continued technical refinement and rigorous multicenter validation will ultimately define its optimal role within contemporary evidence-based obstetric practice.

5. Conclusions and Future Directions

This updated systematic review extends the foundational synthesis by Pergialiotis et al. [23], incorporating an additional decade of evidence across HI, UI, and ECC settings. Taken together, the current data indicate that while double cerclage does not uniformly outperform single techniques across all patient populations, it demonstrates comparable efficacy and safety—and may confer distinct advantages in cases of advanced cervical change or high obstetric risk.

Looking ahead, forthcoming multicenter randomized trials (such as COSA), together with advances in suture biomaterials, AI-assisted imaging for procedural precision, and the development of international registry networks, are expected to refine patient selection criteria and promote global standardization of cerclage practice. Further mechanistic research integrating biomechanical modeling and immunologic barrier studies will be essential to define the conceptual spectrum linking preventive and interventional strategies in cervical insufficiency.

Ultimately, the goal is to integrate double-level cerclage into individualized, evidence-based obstetric care—balancing mechanical reinforcement and biological protection to prevent recurrent mid-trimester loss and extreme preterm birth among the most vulnerable women. As evidence matures and standardization progresses, double cerclage has the potential to transition from an empirically derived rescue procedure to a core element of precision perinatal medicine.