Review

The Role of Sonographic Cervical Length in Labor Induction at Term Jessica Papillon-Smith, MD,1 Haim A. Abenhaim, MD, MPH, FRCSC1,2 1

Department of Obstetrics and Gynecology, Jewish General Hospital, McGill University, 5790, Cote-Des-Neiges Road, H412, Montreal, Quebec, H3T 1E2, Canada 2 Centre for Clinical Epidemiology and Community Studies, Jewish General Hospital, McGill University, 5790 CoteDes-Neiges Road, H412, Montreal, Quebec, H3T 1E2, Canada Received 7 January 2014; accepted 26 July 2014

ABSTRACT: The purpose of this study is to review the literature examining the role of ultrasound in the induction of labor. Databases including Ovid, PubMed, Web of Science, Google Scholar, and UpToDate were searched and current guidelines from the SOGC, the ACOG, the RCOG, and the RANZCOG were reviewed. Although studies have not demonstrated the superiority of cervical sonography to the Bishop score, the evidence indicates that sonography could be useful in planning induction of labor, significantly reducing the need for cervical ripening agents. A more comprehensive method integrating both sonography and digital exam may be more C appropriate. V 2014 Wiley Periodicals, Inc. J Clin Ultrasound 43:7–16, 2015; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jcu.22229 Keywords: Bishop score; cervical length; endovaginal ultrasound; induction of labor

L

abor induction at term is one of the most commonly practiced obstetrical interventions in North America.1–3 Rates of induction of labor (IOL) for both elective and medical purposes are steadily increasing2 and have more than doubled over the past two decades, reaching approximately 20%.4 The inherent risks associated with labor induction, especially in nulliparas, are well known. These mainly include higher rates of prolonged labor as well as an increased need for cesarean delivery.2,5–10 Moreover, IOL is associated with an increased rate of operative delivery, abnormal fetal heart rate Correspondence to: H. A. Abenhaim C 2014 Wiley Periodicals, Inc. V

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patterns, tachysystole, uterine rupture, iatrogenic preterm delivery, as well as lengthy hospitalizations and additional health care costs2,5 Given the morbidity associated with this increasingly prevalent practice, there has been a growing need for a model that judiciously guides in the planning of IOL and that accurately predicts its likelihood of success. The purpose of this study is to review the literature that evaluates whether sonography could play a role in the labor induction process. METHODS

We carried out a literature review using Embase (Ovid), Medline, PubMed, Web of Science, Google Scholar, and UpToDate. We used the following MeSH terms to identify relevant articles: “induction of labor at term”, “Bishop score”, “transvaginal ultrasound”, and “cervical length”. Prospective observational studies, randomized controlled trials, and systematic reviews published prior to October 2012 were used to address specific questions pertaining to the use of ultrasound in labor and delivery. Articles were initially screened and selected by one author and then compared with the second author. Articles were categorized into several clinical contexts: (1) ultrasound in predicting onset of labor at term, (2) ultrasound in predicting the success of labor induction, and (3) ultrasound in determining need for cervical ripening with prostaglandins. Finally, current practice guidelines published by the Society of Obstetricians and Gynecologists of Canada, the American Congress of Obstetricians and 7

PAPILLON-SMITH AND ABENHAIM TABLE 1 The Ability of Ultrasound in Predicting the Spontaneous Onset of Labor at Term: Prospective Cohort Studies

First Author and Reference No.

Gestational Age (weeks) at Time of Ultrasound

Year of Publication

Number of Subjects

Parameters Studied

2008

1,864

2008

206

2006

97

TVUS: CL Maternal features TVUS: CL Parity TVUS: CL BS

Ramanathan et al12

2003

1,571

TVUS: CL

37

Rozenberg et al15

2000

128

TVUS: CL BS FFN

3914 to 4013

Rao et al14 Vankayalapati et al11 Strobel et al

13

41 4113 4114 to 4212

Labor Onset Within 10 days Within 4 days Within 24 h 48 h 96 h Prior to 41 weeks Within 7 days

Sonographic Cervical Length Can Predict the Probability of Spontaneous Labor Within the Suggested Time Frame Yes Yes, in nullips. Yes, in nullips. and multips. Yes, in nullips. only No Yes Yes

Abbreviations: TVUS, endovaginal ultrasound; CL, cervical length; nullips., nulliparous women; BS, Bishop score; multips., multiparous women; FFN, fetal fibronectin.

RESULTS

indeed be useful in predicting the spontaneous onset of labor within a suggested time frame. However, it is difficult to draw conclusions regarding the practicality of ultrasound for this specific purpose given both the different methods used and the outcomes measured in these studies.

Predicting the Spontaneous Onset of Labor

Predicting the Success of Labor Induction

One of the major concerns in IOL planning involves discerning the patients who will inevitably require induction from those who will experience the spontaneous onset of labor. Thus, several observational studies were conducted in an effort to assess whether sonographic cervical parameters, namely cervical length (CL), were useful in predicting this outcome (Table 1). The studies reviewed are rather heterogeneous in nature, with some measuring CL at an early date (Ramanathan et al at 37 weeks),11 while others refer to later gestational ages (Vankayalapati et al at 4113 weeks).11,12 Furthermore, these studies evaluate different time frames during which labor onset should occur. Indeed, Strobel et al claim that CL can accurately predict labor onset within 48 hours only, whereas others, such as Rao et al, claim that CL can predict the onset of labor within over 1 week.13,14 Finally, the CL cutoffs judged as being useful in predicting the spontaneous onset of labor varied from 13.9 mm in the study by Strobel et al to 26 mm in the study by Rozenberg et al.13,15 Despite their heterogeneity, each of these studies establishes that sonographic CL can

Typically, clinicians rely on cervical favorability, determined by the Bishop score, to assess the likelihood of IOL success. However, our ability in foretelling this result is rather poor.16 For this reason, several observational studies were performed in hopes of establishing a system that can accurately predict the outcome of IOL. Most of these studies compared the predictive value of digital exam to sonography, while others created models that incorporate elements of both.

Gynecologists, the Royal College of Obstetricians and Gynecologists, as well as the Royal Australian and New Zealand College of Obstetricians and Gynecologists were reviewed.

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Digital Exam Advocates. Fourteen prospective observational studies were reviewed that concluded that elements of the digital exam, either the Bishop score, the modified Bishop score, or dilatation alone, were better predictors of IOL success than sonography (Table 2). Both Gonen et al and Rozenberg et al state that once the Bishop score is known, the addition of sonographic findings does not improve the ability to predict the outcome of IOL.17–19 The study by Chandra et al draws similar conclusions; however, they add that sonography might play a role when the cervix is closed and effacement cannot be determined digitally.20 JOURNAL OF CLINICAL ULTRASOUND

SONOGRAPHY IN LABOR INDUCTION AT TERM TABLE 2 Digital Exam versus Ultrasound in Predicting the Success of Labor Induction: Prospective Cohort Studies Digital Exam Advocates Bishop Score Proponents

Year of Publication

Aragao et al66 Tanir et al67 Park et al21 Eggebo et al65 Yanik et al68 Gomes et al69

N

Primary Outcome

2011 2009 2009 2008 2007 2006

126 43 110 275 73 191

Rozenberg et al18

2005

266

Rozenberg et al19 Roman et al51 Roman et al52

2005 2004 2004

266 106 90

Chandra et al20 Gonen et al17

2001 1998

122 86

VD VD < 24 h Entering active phase VD Mode of delivery VD > 24 h CD Induction-delivery interval Induction-VD int. CD Fail to enter active phase Duration latent phase Duration labor VD VD

Dilatation Proponents

Year

N

67

Tanir et al Roman et al52

2009 2004

43 90

Watson et al50

1996

Cutoff for Bishop Score 4 >5 2 cm 2 cm 2 cm —

— HR 2 HR 2.33 —

Year

N

Primary Outcome

Cutoff for Modified BS

Result

2003

134

Duration labor Duration latent phase

2 2

aOR 2.928 aOR 2.878

Other Modified BS: (dilatation 1 effacement) Reis et al

49

Abbreviations: N, number of subjects; BS, Bishop score; VD, vaginal delivery; OD, odds ratio; CD, cesarean delivery; HR: hazard ratio; aOR, adjusted odds ratio.

Naturally, with a favorable Bishop score, one is often confident that IOL will be successful; so further knowledge of sonographic elements is of no value. However, one is rarely as confident of the outcome with the finding of a closed, unfavorable cervix. Chandra et al thus hypothesize that digital exam is superior to ultrasound in the setting of a ripe cervix, but that its value is not as clear when an unripe cervix is found.20 In one of their studies, Park et al also conclude that sonography is impractical in predicting IOL outcome.21 However, their assessment was limited to parous women. Their study on nulliparas suggests that sonography seems to be a valuable tool in predicting IOL outcome.22 This suggests that parity is a significant effect modifier and that digital exam may be a superior tool in multiparas only. Sonographic Advocates. Contrary to the studies listed in Table 2, 32 prospective observational studies published over the past 20 years establish that sonographic cervical elements are superior to digital examination in predicting VOL. 43, NO. 1, JANUARY 2015

IOL outcome (Table 3). These studies mainly evaluate sonographic CL, but also evaluate the role of other findings, namely posterior cervical angle, funneling, sonographic dilatation, shape of the cervical canal, and head-perineal distance. Some of these studies provide both an idea of sonography’s predictive capacity and CL cutoffs deemed useful. For instance, Pandis et al state that with a CL 31 mm increases one’s likelihood of remaining undelivered at 24 hours to 85%.23 As hypothesized by Chandra et al, a proponent of the digital exam, Gabriel et al demonstrate that sonographic CL is not predictive of IOL outcome when the Bishop score is favorable (>5).24 However, with an unripe cervix (Bishop score 26 mm doubles a woman’s risk for cesarean delivery.20,24 Caliskan et al, a group from Turkey, designed a study specifically 9

PAPILLON-SMITH AND ABENHAIM TABLE 3 Digital Exam versus Ultrasound in Predicting the Success of Labor Induction: Prospective Cohort Studies Ultrasound Proponents Cervical Length Proponents

Year

N

Primary Outcome

Cutoff

Result

Keepanasseril et al70 Gomez-Laencina et al26 Torricelli et al71 Bastani et al72 Sieroszewski et al73 Cheung et al74 Uyar et al75 Tanir et al67 Tan et al27 Meijer-Hoogeveen et al28

2012 2012 2011 2011 2010 2010 2009 2009 2009 2009

311 177 50 200 101 460 189 43 231 102

VD CD VD< 24 h CD VD VD VD VD < 24 h VD < 24 h CD

OR 0.005 OR 11.77 OR 2.02 — — aOR 0.59 aOR 1.206 — aOR 5.6 OR 1.07 OR 1.14

382 240 179 77 100 53

VD < 24 h VD CD CD Active phase VD < 60 h VD CD VD > 24 h Duration labor VD CD Duration labor VD < 24 h CD CD for FTP Active phase < 2 days Induction-VD int. VD < 24 h CD CD VD < 24 h CD VD VD < 24 h Duration latent phase

Longer 25.2 mm Shorter >19 mm 19 mm 20 mm Measured supine Measured upright 30 mm 25 mm >20 mm >20 mm 26 mm 34 mm 30 mm Longer ? Longer Longer Longer 30 mm Longer ? Longer Longer Longer