Cerclage for short cervix on ultrasonography: meta-analysis of trials using individual patient-level data

OBJECTIVE: Preterm birth is the main cause of perinatal morbidity and mortality. A short cervical length on transvaginal ultrasonography predicts preterm birth. Our aim was to estimate by meta-analysis of randomized trials whether cerclage prevents preterm birth in women with a short cervical length. DATA SOURCES: MEDLINE, PubMed, EMBASE, and the Cochrane Library were searched with the terms "cerclage," "cervical cerclage," "short cervix," "ultrasound," and "randomized trial." We included randomized trials involving the use of cerclage in women with short cervical length on transvaginal ultrasonography using patient-level data. TABULATION, INTEGRATION, AND RESULTS: Four properly conducted trials were identified. In the total population, preterm birth at less than 35 weeks of gestation occurred in 29.2% (89/305) of the cerclage group, compared with 34.8% (105/302) of the no-cerclage groups (relative risk [RR] 0.84, 95% confidence interval [CI] 0.67-1.06). There was no significant heterogeneity in the overall analysis (P = .29). There was a significant reduction in preterm birth at less than 35 weeks in the cerclage group compared with the no-cerclage groups in singleton gestations (RR 0.74, 95% CI 0.57-0.96), singleton gestations with prior preterm birth (RR 0.61, 95% CI 0.40-0.92), and singleton gestations with prior second-trimester loss (RR 0.57, 95% CI 0.33-0.99). There was a significant increase in preterm birth at less than 35 weeks in twin gestations (RR 2.15, 95% CI 1.15-4.01). CONCLUSION: Cerclage does not prevent preterm birth in all women with short cervical length on transvaginal ultrasonography. In the subgroup analysis of singleton gestations with short cervical length, especially those with a prior preterm birth, cerclage may reduce preterm birth, and a well-powered trial should be carried out in this group of patients. In contrast, in twins, cerclage was associated with a significantly higher incidence of preterm birth.     

疑似宫颈机能不全的保守治疗

超声检测宫颈长度可以辅助诊断宫颈机能不全,但是无统一标准,妊娠中期渐进性无痛性宫颈扩张或缩短为可疑宫颈机能不全, 同时伴有早产史或晚期流产史者更符合宫颈机能不全。妊娠中期宫颈长度<25 mm早产风险显著增加,为可疑宫颈机能不全。对于无早产史或晚期流产史者孕妇行环扎术无显著降低早产率的证据,但宫颈长度≤20 mm应用孕酮显著减少了不同孕周的早产率,显著改善了围产儿的结局。对于有早产史或晚期流产史伴宫颈长度<25mm者应用孕酮、环扎和宫颈托均有益处,可据患者意愿和医生的经验选择个体化处理方案。     

Effectiveness of dydrogesterone, 17-OH progesterone and micronized progesterone in prevention of preterm birth in women with a short cervix

Objective: To compare the efficacy of dydrogesterone, 17-OH progesterone (17OHP) and oral or vaginal micronized progesterone with cerclage for the prevention of preterm birth in women with a short cervix.

Methods: The study included 95 women with singleton gestation and cervical length (CL) ≤?25?mm. Among these, 35 women were asymptomatic at 15–24?weeks and 60 had symptoms of threatened late miscarriage (LM) or preterm delivery (PD) at 15–32 weeks. Patients were randomized to receive dydrogesterone, 17OHP or oral/vaginal micronized progesterone; after one week of therapy 15 women underwent cerclage.

Results: Efficacy of vaginal progesterone (VP) for the prevention of preterm birth reached 94.1%. In asymptomatic women pregnancy outcomes were comparable to cerclage. In women with threatened LM/PD, combination therapy with VP, indomethacin and treatment of bacterial vaginosis (BV) with the subsequent use VP until 36?weeks together with CL monitoring significantly decreased the rate of preterm birth (RR 0.01; 0.0001–0.24) and low birth weight (LBW) (RR 0.04; 0.01–0.96). CL increase during the first week of treatment with a subsequent plateau phase indicated treatment efficacy. Dydrogesterone, 17OHP, and micronized oral progesterone (OP) were associated with PD in 91.7% of women.

Conclusions: Combination management strategy including VP significantly benefits pregnancy outcomes in women with a short cervix compared with cerclage. Dydrogesterone, 17OHP, and OP were not found to be efficacious.     

Guideline No. 398: Progesterone for Prevention of Spontaneous Preterm Birth

ObjectivesTo assess the benefits and risks of progesterone therapy for women at increased risk of spontaneous preterm birth (SPB) and to make recommendations for the use of progesterone to reduce the risk of SPB and improve postnatal outcomes.OptionsTo administer or withhold progesterone therapy for women deemed to be at high risk of SPB.OutcomesPreterm birth, neonatal morbidity and mortality, and postnatal outcomes including neurodevelopmental outcomes.Intended UsersMaternity care providers, including midwives, family physicians, and obstetricians.Target PopulationPregnant women at increased risk of SPB.EvidenceMedline, PubMed, EMBASE, and the Cochrane Library were searched from inception to October 2018 for medical subject heading (MeSH) terms and keywords related to pregnancy, preterm birth, previous preterm birth, short cervix, uterine anomalies, cervical conization, neonatal morbidity and mortality, and postnatal outcomes. This document represents an abstraction of the evidence rather than a methodological review.Validation MethodsThis guideline was reviewed by the Maternal–Fetal Medicine Committee of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and approved by the SOGC Board of Directors.Benefits, Harms, and/or CostsTherapy with progesterone significantly reduces the risk of SPB in a subpopulation of women at increased risk. Although this therapy entails a cost to the woman in addition to the discomfort associated with its use, no other adverse effects to the mother or the baby have been identified.SUMMARY STATEMENTS (GRADE ratings in parentheses)

• 1Progesterone therapy reduces the risk of spontaneous preterm birth in women at an increased risk based on history of previous spontaneous preterm birth or in women with a short cervical length (moderate).
• 2There is insufficient evidence to support the use of progesterone for prevention of spontaneous preterm birth in women with a pregnancy in the absence of cervical shortening (moderate).
• 3There is insufficient evidence to support the use of progesterone for prevention of spontaneous preterm birth in women with a normal cervical length and a prior conization procedure on the cervix or abnormal uterine anatomy (low).
• 4Use of progesterone in women with arrested preterm labour is not associated with a reduced risk of spontaneous preterm birth or with improved postnatal outcomes (moderate).
• 5Use of vaginal progesterone for prevention of spontaneous preterm birth has not been associated with an increase in congenital malformations or with a worsening of postnatal neurodevelopmental outcomes (moderate).

RECOMMENDATIONS (GRADE ratings in parentheses)

• 1In women with a singleton pregnancy and a short cervical length (≤25 mm by transvaginal ultrasound between 16 and 24 weeks), vaginal progesterone therapy for prevention of spontaneous preterm birth is recommended (strong/moderate).
• 2In women with a previous spontaneous preterm birth, vaginal progesterone therapy for prevention of spontaneous preterm birth is recommended (strong/moderate).
• 3In women with a twin pregnancy (and by extrapolation of data, with a higher-order multiple pregnancy) and with a short cervical length (≤25 mm by transvaginal ultrasound between 16 and 24 weeks), vaginal progesterone therapy for prevention of spontaneous preterm birth is recommended (strong/moderate).
• 4In patients with a singleton pregnancy and a previous spontaneous preterm birth or a cervical length ≤25 mm between 16 and 24 weeks in the current pregnancy, if a cerclage is being considered, vaginal progesterone should be offered as an effective and potentially superior alternate therapy (strong/moderate).
• 5In patients using progesterone for prevention of spontaneous preterm birth, additional therapies such as a cervical cerclage (with exception of a rescue cerclage for an examination-based diagnosis) or a pessary are not recommended (strong/moderate).
• 6In patients at increased risk of spontaneous preterm birth due to a previous preterm birth, a short cervical length in the current pregnancy, or a multiple pregnancy, bed rest or reduced activity is not recommended (strong/moderate).
• 7When indicated for prevention of spontaneous preterm birth in a singleton pregnancy, vaginal micronized progesterone in a daily dose of 200 mg is recommended (strong/moderate).
• 8When indicated for prevention of spontaneous preterm birth in a multiple pregnancy, vaginal micronized progesterone in a daily dose of 400 mg is recommended (conditional [weak]/low).
• 9When indicated, vaginal progesterone therapy should be initiated between 16 and 24 weeks gestation, depending on when the risked factor is identified (strong/moderate).
• 10With consideration of individual patient risk factors, vaginal progesterone therapy can be continued up to 34–36 weeks gestation (strong/moderate).

     

Current options for mechanical prevention of preterm birth

Cervical insufficiency can be defined by a combination of obstetric history, cervical dilation on exam, and/or short cervical length in women with prior preterm birth. Options for mechanical intervention include cerclage and pessary. There is evidence to support the benefit of a cervical cerclage in women with singleton gestations who have a diagnosis of cervical insufficiency either based on second trimester painless cervical dilatation leading to recurrent early preterm births, or a history of early spontaneous preterm birth and a second trimester transvaginal ultrasound short cervical length or cervical dilation on exam. For women with multiple gestations, the benefit of a cerclage is uncertain, and further study is warranted. The pessary has also been studied for mechanical prevention of preterm birth in various populations, however the results so far have been mixed and warrants further study prior to routine use.     

Clinical management of the short cervix

Cervical cerclage is associated with prolongation of gestation in singleton pregnancies with prior spontaneous preterm delivery and a short cervix on vaginal ultrasonography in the mid-trimester. Ultrasound screening of cervical length is not indicated in low-risk singleton pregnancies and in women with multiple gestations. 17α-Hydroxyprogesterone does not prevent preterm delivery in twin gestations with a short cervix. Cervical cerclage may cause detrimental effects in twin gestations. Vaginal pessary for the prevention of preterm birth in women with a short cervix is currently under active investigation.     

Cervical length and prediction of preterm delivery

PURPOSE OF REVIEW: To present a summary of the literature and most recent advances in the clinical use of cervical length for the prediction of preterm birth. RECENT FINDINGS: Cervical length is predictive of preterm birth in all populations studied, including asymptomatic women with prior cone biopsy, mullerian anomalies, or multiple dilation and evacuations. While cervical length remains the most predictive measurement, funneling may add to its predictive value in certain populations. In terms of interventions aimed at preventing preterm birth once a short cervical length has been identified in asymptomatic women, recent data from a meta-analysis of all trials published so far point to the benefit of ultrasound-indicated cerclage in women with both a prior preterm birth and a cervical length less than 25 mm. Other interventions for a short cervical length such as progesterone and indomethacin are promising, but deserve further study before clinical recommendations can be made. In women with symptomatic preterm labor, a recent trial has shown that knowledge of cervical length (and fetal fibronectin) may be beneficial both in terms of time to triage and reduction of preterm birth. SUMMARY: Transvaginal ultrasound cervical length used as a screening tool for prediction and prevention of preterm birth can significantly improve the health outcomes of pregnant patients and their babies.     

Contemporary use of cervical cerclage

Although it was devised over 50 years ago, only recently controlled randomized trials have evaluated the efficacy of cervical cerclage. Cerclage was originally devised for women with both prior preterm birth (PTB) and cervical changes in the current pregnancy. Evidence suggests that transvaginal cerclage probably prevents second trimester loss/PTB in women with >or=3 PTB/second trimester loss (history-indicated cerclage best placed at 12 to 14 wk); and in women with a prior PTB 16 to 36 weeks and transvaginal ultrasound cervical length<25 mm in the current pregnancy (ultrasound-indicated cerclage at 14 to 23 6/7 wk).     

Short cervix syndrome: current knowledge from etiology to the control

Background

Preterm delivery is one of the most serious public health problems and is the most important factor relating to neonatal morbidity and mortality. The strategies for preventing it include understanding the risk factors, with specific interventions. Recently, uterine cervix measurements using ultrasonography and vaginal administration of progesterone have gained importance in predicting and secondarily preventing spontaneous preterm delivery.

Objective

To describe the short cervix syndrome, including its etiology, diagnosis, and possible therapies.

Methods

Research in ISI, Pubmed, and Scielo database using the words short cervix, preterm delivery, sludge, cervical funneling, cervical gland area, progesterone, cerclage, and pessary.

Results

We found a lot of articles about this topic, including randomized controlled trials. The etiology is multifactorial, being the diagnosis based in a cervix shortening at 20–24 weeks. The history and measurement of cervix length by transvaginal ultrasound have been shown to be effective to select the high risk pregnancies. The progesterone, cervical cerclage, and cervical pessary showed to be effective to reduce the preterm delivery in pregnant women with short cervix.

Conclusion

The successful management of pregnant women presenting a short cervix depends on the understanding that cervical shortening is the final common path for several causes of preterm delivery. The best approach should be individualized to each patient.     

Novel developments on cervical length screening and progesterone for preventing preterm birth

Cervical length (CL) measured by transvaginal ultrasound is an effective screening test for the prevention of preterm birth (PTB). The criteria for an effective screening test are all met by CL. It studies an important condition (PTB); it is safe and acceptable by >99% of women; it recognises an early asymptomatic phase that precedes PTB by many weeks; it has a well-described technique, is reproducible, is predictive of PTB in all populations studies so far; and, perhaps most importantly, it has been shown that 'early' treatment is effective in prevention. These two interventions, effective only in specific populations, are ultrasound-indicated cerclage and vaginal progesterone.     

Is mid-trimester cervical length screening effective for reduction of threatened preterm labor?

ObjectiveTo assess the incidence of threatened preterm labor and preterm labor admissions and treatment of women with singleton gestations and no prior preterm birth before and after implementation of the universal mid-trimester transvaginal ultrasound cervical length screening.Materials and methodsA retrospective cohort study included of singleton gestations without a history of preterm birth presenting with threatened preterm labor between 24 0/7 and 36 6/7 gestational week in two study periods: before and after the implementation of the universal cervical length screening. Women with cervical length <25 mm were considered being at high risk for preterm birth and were prescribed a treatment with vaginal progesterone daily. The primary outcome was the incidence of threatened preterm labor. Secondary outcomes were the incidence of preterm labor.ResultsWe have found a significant increase in the incidence of threatened preterm labor from 6.42% (410/6378) in 2011 to 11.61% (483/4158) in 2018 (p < 0.0001). Gestational age at triage consult was lower in than in 2011, although the rate of admission for threatened preterm labor was similar in both periods. There was a significant decrease in the incidence of preterm delivery <37 weeks from 25.60% in 2011 to 15.94% in 2018 (p < 0.0004). Although there was a reduction in preterm delivery ≤34 weeks, this reduction was not significant.ConclusionThe universal mid-trimester cervical length screening in asymptomatic women is not associated with a reduction in the frequency of threatened preterm labor or the admission rate for preterm labor, but reduces the rate of preterm births.     

Cerclage for prevention of preterm birth in women with a short cervix found on transvaginal ultrasound examination: a randomized trial

OBJECTIVE: The purpose of this study was to determine the efficacy of cerclage and bed rest versus bed rest-only for the prevention of preterm birth in women with a short cervix found on transvaginal ultrasound examination. STUDY DESIGN: Women with > or =1 of high-risk factors for preterm birth (> or =1 preterm birth at < 35 weeks of gestation, > or =2 curettages, diethylstilbestrol exposure, cone biopsy, Mullerian anomaly, or twin gestation) were screened with transvaginal ultrasonography of the cervix every 2 weeks from 14 weeks of gestation to 23 weeks 6 days of gestation. Enrollment was offered to both asymptomatic women who were at high risk and who were identified to have short cervix (< 25 mm) or significant funneling (>25%) and nonscreened women who were at low risk and who were identified incidentally. The women who gave written consent were assigned randomly to receive either McDonald cerclage or bed rest-only. Both groups received similar counseling and treatment. Primary outcome was preterm birth at < 35 weeks of gestation. RESULTS: Sixty-one women were assigned randomly. Forty-seven pregnancies (77%) were high-risk singleton gestations. Thirty-one women (51%) were allocated to cerclage, and 30 women (49%) were allocated to bed rest. There were no differences between the groups in demographic characteristics, risk factors, and cervical variables. Preterm birth at < 35 weeks of gestation occurred in 14 women (45%) in the cerclage group and in 14 women (47%) in the bed rest group (relative risk, 0.94; 95% CI, 0.34-2.58). There was no difference in any obstetric or neonatal outcomes. A subanalysis of singleton pregnancies with previous preterm birth at < 35 weeks of gestation and a short cervix of < 25 mm (n = 31 women) also revealed no significant difference in recurrent preterm birth at < 35 weeks of gestation (40% vs 56%; relative risk, 0.52; 95% CI, 0.12-2.17). CONCLUSION: Cerclage did not prevent preterm birth in women with a short cervix. These results should be confirmed by larger trials.     

The prevalence of short cervix between 20 and 24 weeks of gestation and vaginal progesterone for prolonging of gestation

Objective: The objective of this study is to understand the prevalence of short cervical length between 20 and 24 weeks gestation in China and to evaluate the efficacy of micronized progesterone for prolonging gestation in nulliparous patients with a short cervix.

Methods: From May 2010 to May 2015, a total of 25?328 asymptomatic women with singleton pregnancies at Peking University First Hospital had their cervical length routinely measured between 20 and 24 weeks of gestation. A cervical length of 25?mm or less was defined as a shortened cervical length. The therapies prescribed include vaginal micronized progesterone capsules (200?mg each night) or bed rest from 20 to 34 weeks of gestation. The primary outcome was spontaneous delivery before 33 weeks.

Results: (1) One hundred fourteen women had a cervical length of?≤25?mm (0.45%). (2) Twenty-nine of which with previous spontaneous preterm delivery or late pregnancy loss had cervical cerclage, the remaining 85 women by the use of vaginal progesterone or simply resting activity restriction to prevent preterm birth. (3) In 85 nulliparous women treated by progesterone or bed rest, progesterone use in cervical length between 10 and 20?mm was associated with a statistically significant reduction in the incidence of preterm birth at <33 weeks of gestation (9.5% versus 45.5%, p?=?0.02) compared with bed rest. There were no significant differences in cervical length between 20 and 25?mm in their rates of spontaneous preterm delivery at <33 (5.3% versus 3.2%, p?=?0.72), <37 (33.3% versus 54.5%, p?=?0.25), or <35 weeks (14.3% versus 45.5, p?=?0.06) of gestation between vaginal progesterone and bed rest.

Conclusion: The rate of short cervical length was less than expected. Vaginal progesterone is efficacious for the prolonging of gestation in women with a cervical length of 10–20?mm in the mid-trimester for a singleton gestation and nulliparous women. For a cervical length of 20–25?mm in the mid trimester, vaginal progesterone compared with bed rest did not prolong pregnancy.     

Management of a woman with a previous preterm birth

Reducing the impact of preterm birth is one of the challenges in modern obstetric practice. This article provides a case-based discussion of management of women with a previous preterm birth. Estimating the risk of a subsequent preterm delivery can be improved by assessment of obstetric history. Primary preventative strategies include lifestyle advice and modification of pre-pregnancy risk factors. Antenatal care involves increased monitoring and supportive care. The usefulness of screening for preterm birth using cervical length ultrasound or biochemical tests of cervicovaginal secretions lie mainly in their negative predictive value, allowing recognition of women in whom subsequent preterm birth is unlikely. Potential prophylactic therapies in high-risk women include marine oils, progesterone pessaries and cervical cerclage, but none have been shown to improve neonatal outcome. The need for further research is highlighted.     

Management of a woman with a previous preterm birth

Reducing the impact of preterm birth is one of the challenges in modern obstetric practice. This article provides a case-based discussion of management of women with a previous preterm birth. Estimating the risk of a subsequent preterm delivery can be improved by assessment of obstetric history. Primary preventative strategies include lifestyle advice and modification of pre-pregnancy risk factors. Antenatal care involves increased monitoring and supportive care. The usefulness of screening for preterm birth using cervical length ultrasound or biochemical tests of cervicovaginal secretions lie mainly in their negative predictive value, allowing recognition of women in whom subsequent preterm birth is unlikely. Potential prophylactic therapies in high-risk women include marine oils, progesterone pessaries and cervical cerclage, but none have been shown to improve neonatal outcome. The need for further research is highlighted.     

Twin and Preterm Labor: Prediction and Treatment

Twin pregnancies are increasing. Preterm birth is a major health problem with high incidence all over the world. It is known to have a higher incidence in twin pregnancies as well as being higher in IVF/ICSI pregnancies. Prediction of preterm birth in twins through transvaginal cervical length measurement and vaginal fetal fibronectin measurement are good and well-documented methods. However, this could not be applied to IVF pregnancies. Prevention of preterm birth by administration of vaginal natural progesterone or IM synthetic progesterone injections is not effective in twins. The situation was similar with administration of progesterone to IVF twin pregnancies. Prophylactic cerclage for prevention of preterm birth in twins resulted in an increase of the incidence of preterm birth. Tocolytics also are ineffective, although nifedipine may have a role in treatment of threatened preterm birth in twins.     

Ultrasound assessment of cervical length in pregnancy

Cervical length in high-risk women for preterm birth has to be identified before early second trimester. Sequential evaluations lead to high predictive significance. The mean cervical length at 24 weeks is about 35 mm when measured by transvaginal ultrasound. A short cervix is defined as a cervix that is less than 25 mm and funneling, i.e. ballooning of the membranes into a dilated internal os, but with a closed external os. Factors such as short cervical length, uterine anomaly, previous cervical surgery, multiple gestation and positive fetal fibronectin results are associated with preterm delivery. Serial transvaginal ultrasound examinations during the early second trimester would provide longitudinal changes in the cervical length. The use of 17alpha-hydroxyprogesterone caproate and cerclage has shown to be beneficial in preventing preterm delivery. When combined with other predictors such as occiput position, parity, maternal age and body mass index, cervical length is a useful parameter for predicting the feasibility of labor induction and successful delivery.     

The Use of Transvaginal Ultrasound in the Prediction of Preterm Delivery

Despite improvements in obstetric management, the rate of prematurity has not changed appreciably in the last two decades. To address this problem, identification of women at risk is an important objective. Recently, transvaginal ultrasound assessment of cervical length has been shown to be superior to digital examination of cervical dilatation and effacement in the prediction of preterm delivery in both low risk asymptomatic women and those that present with suspected preterm labour. Studies incorporating transvaginal ultrasound into interventional trials are needed to determine the efficacy of cervical length measurement in the prevention of preterm birth.     

Guideline No. 401: Sonographic Cervical Length in Singleton Pregnancies: Techniques and Clinical Applications

Objectives• To assess the association between sonography-derived cervical length measurement and preterm birth.• To describe the various techniques to measure cervical length using sonography.• To review the natural history of the short cervix.• To review the clinical uses, predictive ability, and utility of sonography-measured short cervix.OutcomesReduction in rates of prematurity and/or better identification of those at risk, as well as possible prevention of unnecessary interventions.Intended UsersClinicians involved in the obstetrical management or cervical imaging of patients at increased risk of a short cervix.Target PopulationWomen at increased risk of a short cervix or at risk of preterm birth.EvidenceLiterature published up to June 2019 was retrieved through searches of PubMed and the Cochrane Library using appropriate controlled vocabulary and key words (preterm labour, ultrasound, cervix, cervical insufficiency, transvaginal, transperineal, cervical length, fibronectin). Results were restricted to general and systematic reviews, randomized controlled trials, controlled clinical trials, and observational studies. There were no date or language restrictions. Grey (unpublished) literature was identified through searching the websites of health technology assessment agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.ValuesThe evidence and this guideline were reviewed by the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada, and the recommendations were made and graded according to the rankings of the Canadian Task Force on Preventive Health Care (Online Appendix Table A1).Benefits, Harms, CostsPreterm birth is a leading cause of perinatal morbidity and mortality. Use of the sonographic technique reviewed in this guideline may help identify women at risk of preterm birth and, in some circumstances, lead to interventions that may reduce the rate of preterm birth.SUMMARY STATEMENTS (Canadian Task Force on Preventive Health Care grading in parentheses)

• 1In the general obstetrical population, cervical length is relatively stable over the first 2 trimesters. The natural history of cervical length change may not be useful in identifying women at increased risk of spontaneous preterm birth. Because there may be different patterns, rates, and/or onset of cervical length shortening, repeat assessment of cervical length may be useful in patients at high risk of spontaneous preterm birth (II-2).
• 2Transvaginal sonography can be used to assess the risk of preterm birth in women with a history of spontaneous preterm birth and to differentiate those at higher and lower risk of preterm delivery (II-2).
• 3Cervical length measurement can be used to identify those at increased risk of preterm birth in asymptomatic women at <24 weeks gestation who have other risk factors for preterm birth (uterine anomaly or prior multiple dilatation and evacuation procedures beyond 13 weeks gestation). However, there is insufficient evidence to recommend specific management strategies in this group of women (II-2).
• 4There is no consensus on the optimal timing or frequency of serial evaluations of cervical length. If repeat measurements are performed, they should be done at suitable intervals to minimize the likelihood of observation error (II-2).
• 5No specific randomized trials have evaluated any interventions in asymptomatic women initially diagnosed at or beyond 24 weeks gestation who are at increased risk of preterm birth (e.g., those who have a history of prior spontaneous preterm birth, uterine anomaly, or prior multiple dilatation and evacuation procedures beyond 13 weeks gestation) and who have a short cervical length. However, knowledge of cervicanalal length beyond 24 weeks may help with empiric management strategies for these women, such as relocation and increased surveillance (III).
• 6In women presenting with suspected preterm labour and intact membranes, transvaginal sonographic assessment of cervical length may be used to help stratify the risk of preterm delivery and prevent unnecessary intervention without harm. This information may result in a reduction in late preterm birth, but it is unclear whether it makes a significant clinical difference (II-2B).
• 7Cervical length surveillance is a safe option for patients with a prior sonography indicated cerclage, unclear history of cervical insufficiency, and prior spontaneous preterm birth when compared with routine cerclage based on clinical assessment; it may reduce the need for subsequent cerclage (II-2B).
• 8Transvaginal sonography appears to be safe in preterm prelabour rupture of membranes, but its clinical predictive value is uncertain in this context (II-2).
• 9There is insufficient evidence to support a committee position on the frequency or timing of sonographic cervical length assessment post cerclage. It is unclear if there is significant clinical benefit of such scans (III).
• 10Sonographic cervical length assessment and fetal fibronectin appear to be similar in predictive ability in symptomatic patients, and their combined value may not be significantly different from assessment of cervical length alone. More research is needed in this area (II-2).

RECOMMENDATIONS (Canadian Task Force on Preventive Health Care grading in parentheses)

• 1Transvaginal sonography is the preferred approach for cervical assessment to identify women at increased risk of spontaneous preterm birth, and it can be offered to women at increased risk of preterm birth (II-2B).
• 2Transperineal sonography can be offered to women at increased risk of preterm birth if transvaginal sonography is either unacceptable or unavailable (II-2B). Transabdominal assessment of cervical length may be a useful alternative for screening under certain conditions.

     

Vaginal sonography and cervical incompetence

Uterine contractions, decidual activation, and cervical competence comprise the fundamental components in contemporary models of the spontaneous preterm birth syndrome, but their relative importance and interactive pathways remain poorly defined. Moreover, the traditional concept that the cervix is either competent or incompetent has been challenged because cervical competence more likely functions along a biologic continuum. Cervical incompetence is a clinical diagnosis characterized by recurrent painless dilation and spontaneous midtrimester birth. Although the efficacy of cerclage for cervical incompetence has never been fully confirmed in randomized clinical trials, the role of cerclage has been expanded to include women with "risk factors" for spontaneous preterm birth or nonreassuring sonographic cervical findings in the mid trimester. Evidence from randomized trials suggests that cerclage has limited efficacy in women with risk factors for cervical incompetence. Results of both retrospective cohort series and randomized trials of cerclage in women with shortened cervical length are inconclusive. We believe that women with a prior early spontaneous preterm birth and shortened midtrimester cervical length represent an ideal population for the conduct of a randomized trial of cerclage, which is currently underway.