McDonald vs. Shirodkar cerclage for the prevention of preterm birth in patients with obesity

Introduction

Transvaginal cervical cerclage is a well-established intervention in obstetrics, aimed at reducing preterm birth among patients with an elevated risk of cervical insufficiency. While the McDonald and Shirodkar techniques remain the two predominant approaches for this procedure, the choice between them is often dictated by provider preference and surgical complexity. The McDonald technique involves placing a purse-string suture circumferentially around the cervix, just distal to the vesico-cervical junction [1], 2]. The Shirodkar technique involves placement of this suture more cephalad, at the level of the internal cervical os, by first dissecting the bladder and rectum off the cervix [2], 3].

Several studies have compared the efficacy of the Shirodkar and McDonald techniques for history-, ultrasound-, and exam-indicated cerclages [2], [4], [5], [6], [7], [8], [9], [10], [11]. Overall, these studies have not demonstrated significant differences in their effectiveness for preventing spontaneous preterm birth. Limited evidence has directly compared the efficacy of these two techniques in specific patient populations, such as those with obesity. A recent study suggested that the Shirodkar technique may offer advantages in maintaining gestational length among patients with obesity, possibly due to its placement closer to the internal cervical os [12].

Obesity, defined as a body mass index (BMI) of 30 kg/m² or greater, is a well-established risk factor for adverse pregnancy outcomes [13], 14] yet its impact on cerclage efficacy remains underexplored. The prevalence of obesity in pregnancy is increasing; in 2020, 29.5 % of live births in the United States were to mothers with a pre-pregnancy BMI of 30 kg/m² or greater, and 26.7 % were in the overweight range with a BMI of 25 kg/m² or greater [15]. Prior studies have shown mixed findings regarding the impact of obesity on preterm birth risk, both for patients with and without a cerclage [14], [16], [17], [18], [19], [20], [21], [22], [23]. While prior analyses comparing McDonald and Shirodkar techniques have reported similar outcomes in the general obstetric population, the potential benefit of the Shirodkar’s more proximal placement in mitigating cervical insufficiency in patients with obesity warrants focused investigation.

This study aims to evaluate the comparative effectiveness of McDonald vs. Shirodkar cervical cerclage in patients with obesity. By clarifying the impact of cerclage type on gestational age at delivery and preterm birth risk in this high-risk population, our findings can advance evidence-based pregnancy management and inform best practices to optimize maternal and neonatal outcomes.

Materials and methods

Results

Out of 1,320 patients who received a cerclage between 2018 and 2023, 495 patients with obesity and singleton pregnancies who underwent transvaginal cervical cerclage were included for analysis. Patients were excluded for abdominal cerclage (n=22), multiple gestations (n=22), and missing primary exposure (n=111) or outcome data (n=409, 82 % McDonald and 18 % Shirodkar cerclages). Of the remainder, those with obesity were included in the study. Among these 495 included patients, 375 (76 %) received a McDonald cerclage, and 120 (24 %) received a Shirodkar cerclage. The study population included patients with history-indicated (n=160, 32.3 %), ultrasound-indicated (n=223, 45.1 %), and exam-indicated (n=112, 22.6 %) cerclages. Baseline characteristics of the study population are shown in Table 1 including maternal age, BMI, insurance status, race and ethnicity, nulliparity, and gestational age at cerclage placement, which were similar between the McDonald and Shirodkar groups. Progesterone use and history of preterm birth were also similar between the groups. There were significant differences noted in cerclage indication, with an increased frequency of Shirodkar cerclages in the ultrasound-indicated group compared to other indications (p=0.003).

There were no significant differences between the McDonald and Shirodkar groups in the adjusted or unadjusted analyses for the outcomes of preterm birth at <37 weeks (p=0.98) or at <34 weeks (p=0.30) (Table 2). There were also no significant differences in the outcomes of spontaneous preterm birth at <37 weeks (p=0.75) or at <34 weeks (p=0.36) (Table 3). Gestational age at delivery also did not differ significantly between the groups in both the unadjusted and adjusted analyses (Table 4). The mean gestational age at delivery was 36.4 ± 4.3 weeks for the McDonald group and 35.9 ± 4.7 weeks for the Shirodkar group (p=0.50). Subgroup analyses by cerclage indication (history-, ultrasound-, or exam-indicated) also revealed no significant difference in gestational age at delivery between the two techniques, except for ultrasound-indicated cerclages which favored the McDonald technique (36.6 ± 4.2 weeks vs. 35.0 ± 5.1 weeks, p=0.02) (Figure 1).

Figure 1:

Subgroup analysis of gestational age at birth by cerclage indication and cerclage type.

Discussion

This study evaluated the comparative effectiveness of McDonald and Shirodkar cervical cerclage techniques in patients with obesity. Both techniques demonstrated similar efficacy in prolonging pregnancy, with no significant difference in gestational age at delivery, preterm birth, or spontaneous preterm birth at <37 or 34 weeks. Subgroup analyses by cerclage indication (history-, ultrasound-, or exam-indicated) confirmed these findings, with no difference for history- and exam-indicated cerclages, and greater pregnancy prolongation with the McDonald technique for ultrasound-indicated cerclages.

Prior research comparing McDonald and Shirodkar techniques has generally found comparable efficacy in the prevention of preterm birth across different patient populations [4], [5], [6], [7], [8], [9], [10], [11]. However, the effect of obesity on cerclage efficacy remains underexplored. Nguyen et al. conducted a large retrospective study using California birth data to assess the impact of maternal obesity on preterm delivery in patients with cervical cerclage [16]. Although cerclage type and indication were not evaluated, the study found that obesity did not increase the risk of spontaneous preterm delivery but was linked to higher overall preterm delivery rates, likely due to medical indications. The findings suggest cerclage effectively prevents spontaneous preterm delivery across BMI groups, but obese patients may face increased overall risk from other complications. A retrospective study by Figueroa et al. specifically investigated the interaction between maternal BMI and cerclage type on pregnancy duration [12]. The authors analyzed 95 women receiving McDonald or Shirodkar cerclage at a single institution over approximately 6 years. Shirodkar cerclage extended pregnancy compared to McDonald (36.7 vs. 33.9 weeks; p=0.02), with the greatest effect in obese women (32.6 vs. 28.8 weeks; p<0.01). No differences were seen in normal or overweight women (p=0.63). While these findings suggest that the Shirodkar technique may benefit obese patients, our much larger study found no BMI-related differences in cerclage efficacy, except improved pregnancy prolongation for the McDonald technique for ultrasound-indicated cerclages. Discrepancies may reflect population differences or unmeasured factors, highlighting the need for further research on BMI, cervical anatomy, and cerclage outcomes.

Given the similar efficacy of McDonald and Shirodkar cerclages in this study, the choice of technique in patients with obesity should consider other factors, such as surgeon familiarity, procedural difficulty, and the patient’s specific anatomy. In addition, rates of complications such as bladder injury and need for regional anesthesia for cerclage removal may be higher in Shirodkar compared to McDonald cerclages. Concern about more complications with equivalent benefit may lead providers to favor the McDonald technique. Overall, care can be individualized to consider all of these factors, and this flexibility in clinical decision-making may help optimize outcomes without sacrificing efficacy. Our findings suggest that providers can prioritize patient-centered care and surgical efficiency when determining the appropriate technique for cerclage placement in patients with obesity.

Future research should focus on clarifying the interaction between obesity, cervical anatomy, and cerclage efficacy. While this study found no difference in outcomes between McDonald and Shirodkar cerclages in obese patients, conflicting findings in prior studies highlight the need to explore factors such as cervical length, suture material, and degree of dilation at placement. Investigating the biomechanical impact of cerclage techniques in the context of increased intra-abdominal pressure could provide valuable insights, particularly for obese patients who may experience higher cervical stress. Subgroup analyses, including patients with prior cervical surgery or mid-trimester loss, may help identify those who derive greater benefit from Shirodkar cerclage. Advanced imaging and computational modeling can further elucidate how cerclage placement affects cervical tissue integrity. Additionally, studies assessing long-term maternal and neonatal outcomes will help refine patient selection and optimize management strategies for cervical insufficiency in this high-risk population.

A key strength of this study is its large cohort size, which allowed for robust statistical analyses and subgroup evaluations. Additionally, the inclusion of a diverse patient population enhances the generalizability of the findings. However, the retrospective design introduces potential biases, including unmeasured clinical factors and other confounders that may have influenced the choice of cerclage technique. Data on physician experience, suture material, suture number, and concomitant progesterone use were not collected and thus could not be included in this analysis. The absence of data on secondary outcomes, such as cerclage-associated complications, limits the comprehensiveness of the analysis. Future studies should address these limitations by incorporating prospective designs and broader outcome measures.

Conclusions

Both McDonald and Shirodkar cerclages are effective in prolonging pregnancy in patients with obesity, with no significant difference in gestational age at delivery between techniques. These findings support the use of either method based on procedural considerations and provider expertise, offering flexibility in managing a high-risk population. Further research is needed to confirm these results and explore additional factors that may influence cerclage outcomes.