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Cervical cerclage: an established intervention with neglected potential?

European Journal of Obstetrics & Gynecology and Reproductive Biology, pages 17 - 19

Abstract

Cervical cerclage is a common obstetric procedure, performed in an attempt to reduce the likelihood of late miscarriage and preterm delivery. Many questions still remain unanswered, however, regarding its efficacy and the populations most likely to benefit. Existing studies often use endpoints such as preterm delivery, but associations between preterm birth and more long-term health effects such as neurodevelopmental sequelae are well reported. Such endpoints have often not been addressed in many of the studies to date. This article reviews and appraises the literature and evidence regarding cervical cerclage as well as addressing the questions that, as yet, remain unanswered.

Keywords: Cervical cerclage, Progesterone, Preterm labour.

1. Introduction

Preterm birth, defined as delivery before 37+0 weeks of pregnancy, is a common obstetric condition, complicating nearly 8% of pregnancies within the United Kingdom [1] : 1.4% of births occur before 32 weeks’ gestation and are classified as very preterm [2] , with a mortality of 144/1000. Preterm birth is associated with significant morbidity and is the single most important determinant of quality of life [3] . Up to 10% of infants who survive very preterm birth will develop spastic motor deficits such as cerebral palsy [4] , and a further 25–50% will suffer cognitive, behavioural, attention and socialisation deficits [5] , chronic lung disease, vision defects and hearing loss. As a consequence it has huge psychosocial and emotional effects on individuals and families, and significant cost implications for the health service.

Treatment modalities to reduce the incidence of preterm birth are currently limited. The focus of most current clinical trials and meta-analyses is on progesterone, but cerclage, the insertion of a suture into the cervix in an attempt to maintain its competence, is a common and established intervention in most obstetric units worldwide. It has been neglected by the research community in recent years, and many questions regarding its efficacy, and populations most likely to benefit, still remain unanswered.

Limited amounts of data and evidence to support decisions regarding cerclage are derived from meta-analyses and mostly inadequately powered randomised controlled trials (RCT). The trials which have been performed are now outdated and often lack relevant end points, prolongation of the pregnancy being a commonly assessed outcome measure which may not even be desirable in light of recent evidence with regard to the possible infective aetiology of preterm birth. Prospective studies are urgently called for, not only on new techniques and populations, but also assessing perinatal and long-term morbidity as the primary outcome measure, as is currently happening with progesterone. This is particularly pertinent due to recent advances in neonatal care and survival at gestations of peri-viability and the known associations of preterm birth with long-term neurodevelopmental sequelae.

2. Cerclage classification

The decision for insertion of a cervical cerclage is broadly divided into three groups: history-indicated, ultrasound-indicated or in the acute setting, a rescue cerclage.

2.1. History-indicated cerclage

Studies that have been undertaken to assess the benefits of the insertion of a prophylactic cervical suture based on risk factors ascertained in the history are often poorly designed, and results are conflicting.

Two small RCTs found no benefit from the insertion of an elective cerclage to high-risk women compared with expectant management. One of these studies assessed the impact of numerous risk factors on the subsequent gestation at delivery and short-term perinatal outcome. Eligibility for entry to the study was assessed using a complex scoring system, ascribing a non-evidence based number to each risk factor, based on the assumed likelihood of its association with preterm delivery [6] . The second included women who had either two or more previous late miscarriages/preterm deliveries prior to 37 weeks or one previous delivery prior to 36 weeks and randomised to cerclage or expectant management. Outcome was gestation at delivery and no difference between the two groups was found [7] .

The largest multicentre RCT was conducted by the RCOG working party and included 1299 patients. This concluded that a cervical cerclage in women with a history of three or more late miscarriages or preterm deliveries was associated with a lower rate of preterm delivery before 33 weeks, although there were only 107 patients in this subgroup analysis. There was also no difference in fetal or neonatal outcome [8] . Multiple risk factors were assessed and both singleton and twin pregnancies included. Entry criteria were not well defined and there was a lack of uniformity in study protocols between units; for example suture materials and techniques varied (the impact of this is due to be investigated by an RCT in Birmingham). Many risk factors and certain outcome measures in this and other studies were analysed only in subgroup analysis and therefore may not be suitably powered to draw robust conclusions. This point was emphasised by a Cochrane review in 2012 [9] .

No studies have assessed additional risk factors such as the nature and extent of cervical surgery or the particular characteristics of previous pre-term deliveries as to whether this may identify the women who may benefit most from a cervical cerclage.

2.1.1. Ultrasound-indicated cerclage

There is some evidence to suggest that in a low-risk population, ultrasound-indicated cervical cerclage does not confer benefit. An RCT randomised 253 women with a cervix under 15 mm (screened from 47,123 women) to cerclage or expectant management. The primary outcome measure was delivery before 33 weeks and secondary outcomes included perinatal mortality or significant neonatal morbidity. No difference was found between the two groups [10] , although the trend was towards an important clinical reduction in preterm birth (15%), and in spite of the high number screened, this study was underpowered to detect relevant clinical differences. The total meta-analysis is small for a low-risk analysis (607 women), and the overall best estimate of a relative risk reduction is clinically important although not significant [11] .

An RCT in a high-risk population demonstrated serial ultrasound scanning to be beneficial in women with singleton pregnancies, previous preterm delivery and a cervical length less than 25 mm detected during serial ultrasound between 16 and 21+6 weeks. A reduction in births at less than 24 weeks and perinatal death was reported but not births at less than 35 weeks unless the cervical length was less than 15 mm [12] . These findings were confirmed by a meta-analysis [11] , which found that certain groups may benefit: previous preterm delivery/2nd trimester loss or birth before 36 weeks. Deliveries before 35 weeks were reduced but no effect on perinatal mortality was reported. Overall a 39% significant reduction in preterm birth <35 weeks was reported (relative risk (RR) 0.61, 95% confidence interval (CI) 0.4–0.92), suggesting this may be more effective than in low-risk women, and the effect on perinatal outcome potentially a type 2 error. Certain risk factors such as the influence of a previous cone biopsy could not adequately be evaluated due to small numbers. It was also reported that in twin pregnancies cerclage was associated with a significantly higher incidence of preterm birth, but this association requires further investigation as only 49 pregnancies were included in this analysis.

2.2. Rescue cerclage

Rescue cerclage is the insertion of a suture in a dilated cervix. Evidence regarding its use is limited. Most of the literature is observational, which is likely to be biased, and consenting and randomising this particular group of women makes controlled studies difficult. One RCT did assess the effect of rescue cerclage and bed rest against bed rest alone in women confirmed to have cervical dilatation and prolapse of the membranes between 22 and 23 weeks’ gestation, although the exact dilatation was not reported and both singleton and multiple pregnancies were included. The women who received cerclage delivered 4 weeks later than those on bed rest and a reduction in delivery before 34 weeks was noted [13] . Prolongation of the pregnancy was also demonstrated with rescue cerclage insertion in two non-randomised trials [14] and [15]. These women are particularly prone to infective morbidity, and these neonatal outcomes were not reported.

Studies have not analysed success in relation to cervical dilatation, but from retrospective studies greater than 4 cm is a significant predictor of failure [16] .

3. Different types of cerclage

3.1.1. Transvaginal (McDonald)/high transvaginal (Shirodkar) cerclage

No study has primarily assessed the technique of cervical suture insertion. The two most common techniques are Shirodkar and McDonald. A Shirodkar suture is a transvaginal purse string suture inserted after bladder mobilisation above the level of the cardinal ligaments, and a McDonald suture is inserted lower, at the cervicovaginal junction, without bladder mobilisation. A secondary analysis of singleton pregnancies from four randomised trials in women with a short cervix indicated that was no difference in the delivery rate before 33 weeks’ gestation after confounding variables had been adjusted for, between the two methods, but this study was not powered to assess this question specifically [17] .

3.2. Transabdominal cerclage

Transabdominal cerclage is often used in cases with a failed transvaginal cerclage. A suture is placed either laparoscopically or via a pfannensteil incision at the level of the internal os. The procedure is associated with maternal morbidity and there are no reported randomised studies comparing its effectiveness with other techniques. Data so far are encouraging: they come from one systematic review compiling data from 13 case series [18] and one controlled non-randomised study of transabdominal versus transcervical cerclage in women with a prior failed transvaginal cerclage [19] . The latter study found a lower incidence of perinatal death/delivery prior to 24 weeks’ gestation in women who had undergone transabdominal versus a repeat transvaginal cerclage. No published studies have been reported comparing insertion pre-conceptually versus during the pregnancy.

The laparoscopic versus open approach has not been fully evaluated in a randomised trial but one small retrospective study comprising of 19 patients found that there may be comparable rates in the delivery of a viable infant [20] .

3.3. Occlusion cerclage

Occlusion cerclage, a procedure whereby the epithelial lining of the cervical canal is removed surgically and/or the external cervical os is occluded using a continuous suture, is still being performed despite a lack of evidence for its efficacy. One RCT aimed to assess the use of occlusion cerclage in 309 women. The end point was the proportion of infants discharged alive from hospital from all pregnancies. The trial was prematurely stopped, however, due to slow recruitment and a failure to demonstrate any benefit of occlusion cerclage on the neonatal survival to discharge, at interim analysis [21] . More importantly it cannot be concluded that the use of occlusion cerclage does not actually cause harm, as numbers were small: in the therapeutic trial, which included 96 patients, the take-home baby rate was 81% in women randomised to cerclage and occlusion, versus 85% in women randomised to routine cerclage (RR 0.96, 95% CI 0.79–1.16) [21] .

4. Adjuvant therapies

No RCTs have been published to assess the efficacy of adjunctive therapy such as progesterone used with cervical cerclage. Observational studies, however, have not reported any benefit, although numbers are small and there are confounding factors such as the use of other therapies including antibiotics and tocolytics [22] . Predictors of pre-term labour may be used in conjunction with ultrasonography to assess the women at highest risk of pre-term delivery and when to administer steroids to promote fetal lung maturity [23] .

5. Suture material

The suture material used for cerclage has also not been adequately assessed. Mersilene tape is commonly used due to its strength, but it has a braided structure and it has been proposed that this is more likely to cause infection [24] . An RCT comparing braided versus non-braided suture material is required.

6. Conclusions and the future

In spite of cerclage being a common intervention (up to 0.42% of pregnancies in the USA [25] ), the actual groups that benefit are limited, but include women with three prior adverse events, and those with a short cervix (<25 mm) who have had a prior preterm birth. Definitive studies are required to answer many questions ranging from benefit in subgroups, different procedures, and longer-term endpoints. A recent paper suggested that cerclage is likely to have a far greater (threefold) benefit on reducing preterm birth than progesterone [26] (0.15 rate reduction in comparison to 0.05). The current enthusiasm for progesterone research should not detract from research on this established procedure. Ultimately combining interventions will need to be evaluated.

Acknowledgement

Staff in Women's Services at St Thomas's Hospital London.

References

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Footnotes

Women's Health Academic Centre. Kings College London, St Thomas's Hospital, Westminster Bridge Road, London SE1 7EH, UK

? Corresponding author at: Division of Women's Health, 10th Floor, North Wing, St Thomas's Hospital, Westminster Bridge Road, London SE1 7EH, UK. Tel.: +44 0 207 188 3639.