Signiﬁcance of cervical ripening in pre induction

Significance of cervical ripening in pre-inductiontreatment for premature rupture of membranes at term

Kentaro Kurasawa1, Megumi Yamamoto1, Yuki Usami1, Aya Mochimaru1,Akihiko Mochizuki1, Shigeru Aoki1, Mika Okuda1, Tsuneo Takahashi1 andFumiki Hirahara2

1Perinatal Center for Maternity and Neonate, Yokohama City University Medical Center, and 2Department of Obstetrics andGynecology, Yokohama City University School of Medicine, Yokohama, Kanagawa, Japan

Abstract

Aim: This study aimed to determine whether mechanical cervical dilatation with a laminaria tent in womenwith premature rupture of membranes (PROM) at term may influence the maternal/neonatal outcomes.Methods: We reviewed the medical records and histopathologic results of the placenta in 782 women withPROM at term. Of the 486 women seen prior to 2010 (group 1), 85 had Bishop scores of 5 or less and underwentinsertion of laminaria tents (group A). In the 296 women admitted after 2010 (group 2), 27 had Bishop scoresof 5 or less and underwent labor management without insertion of laminaria tents (group B). The patientcharacteristics, delivery course and neonatal outcomes were compared between the groups.Results: There were no significant differences in the maternal age, percentage of nulliparas, body mass index,gestational age at delivery or Bishop score between the groups. The Bishop score improved from 2.5 to 6.1 afterlaminaria tent insertion in group A. However, there were no significant intergroup differences in the fre-quency of use of labor-inducing agents or the time interval from PROM to delivery. The incidence of clinical/pathological chorioamnionitis was not higher in group A than in group B. No significant differences werefound in the Apgar scores, umbilical artery pH or frequency of asphyxia neonatorum between the groups.Mechanical cervical dilatation by laminaria tent insertion neither increased the incidence of infection norcontributed to improvement of the perinatal prognosis.Conclusion: Mechanical cervical dilatation does not provide any benefit for women with PROM at term.Key words: Bishop score, cervical ripening, induction, laminaria, premature rupture of membrane.

Introduction

Premature rupture of membranes (PROM) is generallyreported to occur at an incidence of approximately 8%.1

Usually, 70% and 95% of women go into labor within24 and 72 h after PROM, respectively.2 The majorpotential problem associated with PROM is ascending

infection; the incidence of infection of the mother andfetus rises with increasing interval to labor afterPROM.3

Some advocate induction of labor, in view of the riskof development of clinical chorioamnionitis (CAM)while waiting for spontaneous labor, particularly inwomen presenting with PROM at or after 37 weeks of

Received: August 6 2012.Accepted: March 4 2013.Reprint request to: Dr Kentaro Kurasawa, Perinatal Center for Maternity and Neonate, Yokohama City University Medical Center,4-57 Urafune-cho, Minami-ku, Yokohama, Kanagawa 232-0024, Japan. Email: [email protected] of interest: None. We confirm that the results of this manuscript have not been distorted by research funding or conflictsof interest.

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doi:10.1111/jog.12116 J. Obstet. Gynaecol. Res. Vol. 40, No. 1: 32–39, January 2014

32 © 2013 The AuthorsJournal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology

mailto:[email protected]

pregnancy, by which time the fetus is expected to havematured sufficiently.1,4,5

Labor can be induced by medications or by mechani-cal cervical ripening treatments. Cervical ripeningtreatments available in Japan include cervical dilatationwith hygroscopic cervical rods (e.g. Laminaria,Dilapan, Lamicel) or with metreurynters (e.g. MiniMetro, Foley catheter). Among the adverse eventsassociated with these cervical ripening treatments,infections of the mother and fetus are of particularimportance.6–8

At present, there is no consensus as yet about thevalidity of employing cervical ripening treatments forpregnant women presenting with PROM.9

The purpose of this study was to determine whethercervical ripening using a laminaria tent may increasethe risk of complications, including infection of themother and fetus, or effectively reduce the time todelivery in women presenting with PROM at term.

MethodsStudy design

In this retrospective study, we enrolled a total of 782women with medically confirmed PROM who wereadmitted to the Yokohama City University MedicalCenter for labor management between September 2008and December 2011. The subjects of this study werewomen in the 37th to 41st week of a single pregnancywith the fetus in the vertex presentation. Womenmeeting the following exclusion criteria were excludedfrom the study: multiple pregnancy; premature labor;post-term delivery; malpresentation such as the pelvicpresentation; history of cesarean section; low-lyingplacenta/placenta previa; uncertain due date; andrupture of membranes during cervical ripening treat-ment after admission for induction of labor.

At our center, we generally induce labor for womenpresenting with PROM at or after 37 weeks of preg-nancy, so as to avoid CAM and fever in the postpartummother. Mechanical cervical ripening treatment hadbeen aggressively performed in women with unfavor-able ripening of the cervical canal, because it is gener-ally recognized that induction of labor is more likely tofail in cases with unfavorable cervical ripening, andthat cesarean section is more frequently necessary inwomen with Bishop scores of 5 or lower.11 However,the most important adverse event of mechanical cervi-cal ripening treatment is infection of the mother andfetus. Because cervical ripening treatment in womenwith ruptured membranes may increase the risk of

infection, caution is required before deciding on suchtreatment. In this connection, we have been carryingout labor management at our institute without the useof cervical ripening treatment with laminaria tentssince October 2010. For this study, a series of 486women with PROM who were treated between Sep-tember 2008 and September 2010, the period duringwhich we performed laminaria tent insertion for unfa-vorable cervical ripening, were classified as group 1,and another series of women with PROM who wereadmitted between October 2010 and December 2011, inwhom labor management was conducted withoutlaminaria tent insertion even in the presence of unfa-vorable cervical ripening, were classified as group 2(296 women); the two groups were compared in regardto the patient characteristics and the perinatal out-comes. Among the 87 women in group 1 in whom thedelivery was managed by laminaria tent insertion, 85had Bishop scores of 5 or lower and were designated asgroup A. Then, 27 women in group 2 with Bishopscores of 5 or lower were designated as group B, and adetailed comparison of the characteristics was con-ducted between group A and group B. The primaryoutcome was determination of the presence/absence ofinfluence of laminaria tent insertion on the risk ofinfection in the mother and fetus. The secondaryoutcome was determination of the influence of lami-naria tent insertion on the time interval from PROM todelivery, to effectively avoid the risk of infection.

Induction protocol

When there was no obvious fluid escaping from thecervix, a diagnosis of PROM was made by the nitrazinetest using the Amnicator. Women who were diagnosedas having PROM were hospitalized, and all were givenantimicrobial drug therapy. At our center, women whocome to the outpatient clinic at 36 weeks of pregnancyare basically subjected to swab cultures of the lowervagina and of the perianal region to screen for group BStreptococci (GBS). In this study, patients who werepositive for GBS were given an i.v. drip infusion of 2 gaminobenzyl penicillin (ABPC) after admission, fol-lowed by administration of 1 g ABPC every 4 h untilthe end of delivery. There was no case of penicillinallergy. Patients who were negative for GBS were givenan oral 100-mg tablet of cefcapene pivoxil after everymeal until the end of delivery.

Fetal cardiotocograms were evaluated immediatelyafter admission to examine the well-being of the fetus.For clinical detection of CAM in the early stage, com-bined evaluation of the maternal body temperature,

Pre-induction treatment for PROM at term

© 2013 The Authors 33Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology

uterine tenderness, blood biochemical data and otherevaluations were carried out.

In group 1, patients who were diagnosed as havinglow Bishop scores by the attending obstetrician under-went laminaria tent insertion and were observed over-night. Approximately 12 h later, namely, the followingmorning, the laminaria tents were removed and deliv-ery was induced. The attending obstetrician selectedoxytocin or prostaglandin F2a as the inducing agent, athis/her discretion. Administration of oxytocin wasbegun at an initial dose of 2 mIU/min, with the doseincreased by 2 mIU/min at intervals of at least 40 min,while ensuring that the final dose did not exceed20 mIU/min. Administration of prostaglandin F2a wasbegun at a dose of 1.5 mg/min, with the dose increasedby 1.5 mg/min at intervals of at least 30 min, whileensuring that the final dose did not exceed 25 mg/min.Oxytocin was used for patients with underlying bron-chial asthma or glaucoma. Patients who had spontane-ous contractions were observed for the progress oflabor.

In group 2, patients were observed overnight,regardless of the Bishop scores. On the followingmorning, labor was induced in patients who did nothave spontaneous contractions. The same methodand dose for labor induction were used as those forgroup A.

The diagnosis of intrauterine infection was madebased on a minor modification of the definition of clini-cal CAM proposed by Lencki et al.10 In mothers withfever (�38.0°C), fulfillment of at least one of the fol-lowing criteria was necessary, while in motherswithout fever, fulfillment of at least three of the follow-ing criteria was necessary: (i) maternal tachycardia; (ii)uterine tenderness; (iii) vaginal discharge/a foul odorof the amniotic fluid; and (iv) leukocytosis (�15 000/mm3). According to the definition by Lencki et al., all

the above four criteria needed to be fulfilled in motherswithout fever. However, it is common for uterineinfection to be clinically established by the time all fourcriteria are fulfilled,11–13 and medical interventions,including pregnancy termination, are often performedbefore this stage. Therefore, at our center, we deter-mined that fulfillment of only three of the criteria wassufficient for the diagnosis.

The present study was conducted with the approvalof the Ethics Review Committee of our center (Yoko-hama City University Medical Center Ethics ReviewCommittee Approval Number: D1203001).

Statistical analysis

We compared the two groups in terms of continuousvariables not showing normal distribution by Mann–Whitney U-test and categorical data by the c2-test. Theodds ratios were calculated to assess the risk of lami-naria tent insertion in the patients with a Bishop scoreof 5 or lower. Post-hoc power was also calculated basedon the observed effect and sample size. Significancelevel was set at P < 0.05. IBM SPSS statistics ver. 19.0 forWindows was used for the statistical analyses.

Results

Among the 782 patients with PROM at term includedin this study, the 486 women in group 1 were treatedduring the period when deliveries were managed atour center with cervical ripening by laminaria tentinsertion, whereas the 296 women in group 2 weretreated after we established a rule to manage deliverieswithout cervical ripening using laminaria tents. Table 1shows the characteristics of the patients in this study.There were no significant differences in the maternalage, percentage of nulliparas, gestational age at deliv-ery, body mass index (BMI) before pregnancy, BMI at

Table 1 Characteristics of the patients in the membrane rupture group as a whole

Characteristics Group 1(n = 486)

Group 2(n = 296)

P-value

Maternal age 32.6 � 5.0 32.8 � 5.6 0.12Percentage of nulliparas 314 (64.6%) 200 (67.6%) 0.40Gestational age at delivery 39.4 � 1.1 39.4 � 1.0 0.32BMI at 1st trimester 21.3 � 3.4 21.1 � 3.1 0.56BMI at delivery 25.2 � 3.3 25.1 � 3.1 0.85Bishop scores 4.7 � 2.3 5.0 � 2.2 0.33Body temperature (°C) 36.6 � 0.39 36.5 � 0.46 0.01Fetal heart rate (b.p.m.) 136.6 � 9.6 135.6 � 10.3 0.13

Values are given as mean � standard deviation or number (percentage). BMI, body massindex.

K. Kurasawa et al.


delivery, Bishop score at admission or the fetal heartrate between the two groups. The maternal body tem-perature was 36.6°C in group 1 and 36.5°C in group 2,with a significant intergroup difference. However,because the body temperature was normal in bothgroups, this difference might have been of little clinicalsignificance.

Table 2 shows the overall delivery course and theneonatal outcomes. In group 1, 87 patients underwentcervical dilatation by laminaria tent insertion. Morethan half of the patients in both groups were deliveredwithout the use of inducing agents. There was no sig-nificant difference in the frequency of use of inducingagents between the two groups. In addition, there wereno significant intergroup differences in the intervalfrom PROM to delivery or the interval from the begin-ning of labor pain to the end of delivery between thetwo groups. Moreover, no significant differences werefound in regard to the frequencies of non-reassuringfetal status (NRFS), meconium staining of amnioticfluid, clinical CAM or emergency cesarean sectionbetween the two groups. The Bishop score on admis-sion was 4.7 � 1.1 in group 1 and 5.0 � 2.2 in group 2,the difference not being statistically significant. Inregard to the neonatal outcomes, no significant differ-ences were found between the two groups in terms ofthe neonatal bodyweight, Apgar score, frequency ofasphyxia neonatorum or umbilical artery pH (UApH).In addition, pathological CAM was diagnosed in 27

patients (CAM grade 1 in 10, CAM grade 2 in sevenand CAM grade 3 in 10 patients) of group 1 and in 15patients (CAM grade 1 in eight, CAM grade 2 in threeand CAM grade 3 in four patients) of group 2, with nostatistically significant intergroup differences.

Table 3 shows the maternal characteristics, deliverycourse and neonatal outcomes in patients who showedunfavorable cervical ripening, with Bishop scores of 5or lower. In group A, 85 patients had Bishop scores of5 or lower and underwent laminaria tent insertion,whereas in group B, 27 patients had similarly lowBishop scores. In comparison to that in patients withruptured membranes as a whole, the percentage ofnulliparas was clearly higher, and the time intervalfrom PROM to delivery was longer in these subgroupsof patients with low Bishop scores. In group A, theBishop score at the time of PROM was 2.5 � 1.5,improving significantly after laminaria tent insertion to6.1 � 2.4. The Bishop score at the time of labor induc-tion was significantly higher in group A than in groupB (P = 0.03). Although there was no significant differ-ence in the frequency of use of inducing agents, pros-taglandin F2a was used more frequently in group Bthan in group A (P < 0.01). The inducing agents used inthe 85 patients in group A were oxytocin in 60, pros-taglandin F2a in five, and oxytocin and prostaglandinF2a in 12 patients. In the 22 patients in group B, oxy-tocin was used in 14 (51.9%), prostaglandin F2a ineight (29.6%), and oxytocin and prostaglandin F2a in

Table 2 Obstetric outcomes in membrane rupture patients as a whole

Characteristics Group 1(n = 486)

Group 2(n = 296)

P-value

Use of laminaria tent 87 0 <0.01Frequency of use of inducing agents 204 (46%) 121 (40.9%) 0.76Changes in Bishop score (in ~12 h) 2.2 1.8 0.77Duration of labor (h) 6.0 (0.6–42.6) 6.7 (0.6–52.9) 0.68Time from rupture to delivery (h) 19.6 (1.1–101.9) 17.1 (0.5–88.7) 0.18Frequency of emergency cesarean section 29 (6.5%) 15 (5.1%) 0.60NRFS 52 (10.7%) 40 (13.5%) 0.24Frequency of meconium staining 74 (15.2%) 47 (15.9%) 0.81Clinical CAM 10 (2.1%) 13 (4.4%) 0.06Amount of bleeding at delivery (g) 349 (58–2062) 385 (51–2112) 0.07Neonatal body weight (g) 3006 � 371 2992 � 348 0.62UApH 7.28 � 0.65 7.27 � 0.88 0.37APS (1) 8.4 � 1.0 8.3 � 1.2 0.23APS (5) 9.2 � 0.6 9.1 � 0.8 0.09Asphyxia Neonatorum 17 (3.5%) 11 (3.7%) 0.87Histological CAM 27/56 (48.2%) 15/32 (46.8%) 0.52

Values are given as mean � standard deviation, median (range) or number (percentage). APS, Apgar score; CAM, chorioamnionitis; NRFS,non-reassuring fetal status; UApH, umbilical artery pH.



five patients (18.5%). It should be noted that the twoagents were not used concomitantly. There were nosignificant differences in the duration of labor or thetime interval from PROM to delivery between the twogroups. Forced delivery as a whole, including forcepsdelivery and vacuum extraction, was required in 17patients (19.5%) of group A and four (14.8%) of groupB, with no statistically significant difference in the per-centage of deliveries requiring medical interventionbetween the two groups (P = 0.78). Although the fre-quencies of emergency cesarean section, clinical CAMand asphyxia neonatorum differed by three-, two- andtwofold, respectively, there were no statistically signifi-cant differences in the frequencies of NRFS, meconiumstaining of the amniotic fluid, clinical CAM or emer-gency cesarean section between the two groups. Thefrequencies of NRFS and meconium staining of theamniotic fluid were similar; however, there were three

patients with both NRFS and meconium staining of theamniotic fluid in group A and one in group B. In regardof the neonatal outcomes, there were no significantintergroup differences in the neonatal bodyweight,Apgar score, frequency of asphyxia neonatorum orUApH. Pathological CAM was found in six patients ingroup A and four patients in group B. The risks ofadverse events associated with laminaria tent insertionare shown in Table 4. The odds ratios were 0.45 forclinical CAM (95% confidence interval [CI], 0.07–2.82),1.39 for cesarean section (95% CI, 0.43–4.57) and 2.27for asphyxia neonatorum (95% CI, 0.27–19.37). Post-hoc power was also calculated; this represents the ret-rospective power of an observed effect based on thesample size and parameter estimates derived from thegiven data. The post-hoc power values of cesareansection, clinical CAM and asphyxia neonatorum were18.3%, 6.3% and 6.4%, respectively.

Table 3 Patient characteristics, obstetric outcomes and neonatal outcomes in patients with Bishop scores of 5 or lower

Characteristics Group A(n = 85)

Group B(n = 27)

P-value

Maternal age (years) 32.5 � 4.9 33.4 � 5.0 0.37Percentage of nulliparas 75 (86.2%) 22 (85.1%) 0.54Gestational age at delivery (weeks) 39.7 � 1.1 39.5 � 1.0 0.43BMI before pregnancy 22.1 � 3.8 21.7 � 2.7 0.62BMI at delivery 26.1 � 3.6 26.1 � 2.5 0.99Bishop score (at admission) 2.5 � 1.5 2.6 � 0.8 0.74Bishop score (12–18 h later) 6.1 � 2.4 4.9 � 2.4 0.03Frequency of use of inducing agents 77 (88.5%) 27 (100%) 0.17Duration of labor 6.9 (0.9–28.2) 6.0 (1.0–13.8) 0.21Time from rupture to delivery 35.2 (5.1–101.9) 39.1 (3.0–77.8) 0.49Total amount of bleeding (g) 408 (58–1935) 567 (120–1596) 0.41Body temperature (°C) (on admission) 36.5 � 0.34 36.5 � 0.41 0.72Body temperature (°C) (following morning) 36.9 � 0.37 36.7 � 0.27 0.24Fetal heart rate (b.p.m.) (on admission) 139.0 � 6.4 133.3 � 10.2 0.04CRP (on admission) 0.67 � 0.78 0.54 � 0.46 0.48Forced delivery 17 (19.5%) 4 (14.8%) 0.78Frequency of emergency cesarean section 11 (12.6%) 1 (3.7%) 0.18NRFS 15 (17.2%) 3 (11.1%) 0.45Frequency of meconium staining 15 (17.2%) 3 (11.1%) 0.45Clinical CAM 3 (3.4%) 2 (7.4%) 0.38Neonatal body weight (g) 2995 � 377 2969 � 351 0.76APS (1) 8.05 � 1.52 8.15 � 1.43 0.76APS (5) 9.10 � 0.65 9.00 � 1.00 0.53UApH 7.28 � 0.06 7.27 � 0.07 0.54Asphyxia neonatorum 7 (8.0%) 1 (3.7%) 0.44Pathological CAM (I–III) 6/11 4/6 0.63

CAM I 2 0CAM II 1 1CAM III 3 3

Admission to NICU 12 (13.8%) 5 (18.5%) 0.55

Values are given as mean � standard deviation, median (range) or number (percentage). APS, Apgar score; CAM, chorioamnionitis; CRP,C-reactive protein; NRFS, non-reassuring fetal status; UApH, umbilical artery pH.

K. Kurasawa et al.


Discussion

The results of this study showed that cervical dilatationby laminaria tent insertion in women presenting withPROM at term was not associated with any increase inthe incidence of intrauterine infection and pathologicalCAM or in the mode of delivery. There was also noreduction in the duration of labor or the time intervalfrom PROM to delivery.

The benefits expected from mechanical cervical dila-tation using laminaria tents or other means includefacilitation of cervical ripening and early completion ofdelivery. It also has the advantage of being less likely tobe associated with excessive contractions.14 It has beenreported that the failure rate of induction and accelera-tion of contractions are higher in patients withextremely unfavorable cervical ripening.15,16 In NorthAmerica and other countries overseas, prostaglandinE2 gel, designed for direct application to the cervicalcanal of the uterus, is used frequently.17,18 In contrast,manual membrane sweep and mechanical cervicaldilatation using laminaria tents are commonly used inJapan. Although it has been reported that cervical dila-tation itself increases the risk of infection in patientswith ruptured membranes,6–8 this remains to be veri-fied. Therefore, the 2011 edition of the guidelines forobstetrical practice in Japan has approved the use ofmechanical cervical dilatation, with due caution paid tothe risk of infection.9 PROM at term has recently beensuggested to be correlated with abnormalities in thecentral nervous system of the fetus, in addition tobeing associated with an increased risk of intrauterineinfection.12,13 Because the fetus may be considered tohave matured sufficiently by term, early completion ofdelivery should be aimed for. However, there is theparadox that the procedure for achieving early comple-tion of delivery may itself increase the risk of infection.Dare et al.5 compared patients with PROM who under-

went induction of labor and those who were observedwithout induction, and found that the incidence ofCAM was lower, and the neonatal intensive care unit(NICU) admission rate was lower, in the former group,with no significant difference in the rate of cesareansection or mechanical vaginal delivery between the twogroups. Thus, they concluded that induction of laborwas an effective medical intervention.

In our study, there was also no decrease in the inci-dence of CAM or the rate of NICU admission. Thesefindings may be primarily explained by our use ofantimicrobial medications in all the patients, althoughit remains controversial whether antimicrobial drugsshould be given to all patients with PROM at term.6

The use of antimicrobial medications might havedelayed the onset of intrauterine infection in ourpatients. Although it has been reported that the timeinterval from PROM to onset of intrauterine infectionis approximately 12–16 h,3 it is known that the risk ofinfection increases as this time interval increases. Inour study, the mean time interval from PROM todelivery was 36 h. The fact that delivery occurredwithin 2 days after PROM under antimicrobialtherapy seems to explain the lack of the difference inthe frequency of CAM between the two groups.Therefore, if no antimicrobial drug(s) had been given,there might have been a difference in the frequency ofCAM, and the use of antimicrobial drugs in this studymight have played an important role. Second, it isspeculated that appropriate medical intervention wasprovided before the establishment of clinical CAM.The diagnostic method proposed by Lencki is com-monly used for making a clinical diagnosis of CAM.However, it has been reported that the neonatal prog-nosis is likely to be already poor at the time that aclinical diagnosis of CAM can be made. It is knownthat the diagnosis of clinical CAM is associated with asignificant increase in the incidence of neonatal sepsisand significantly increased risk of chronic lungdisease, cerebral palsy, and periventricular leukoma-lacia related to fetal inflammatory reaction syndromecaused by hypercytokinemia.11–13,20

The indication for the cesarean section in these 11patients was NRFS (n = 6), prolonged labor (n = 4) ormaternal indication (hypertension; n = 1). One of thepatients with prolonged labor had a mild fever of37.2°C and was judged to have signs of maternal infec-tion, although she did not meet Lencki’s diagnosticcriteria for clinical CAM. It is considered that a clear-cut diagnosis of clinical CAM in this patient wasavoided by provision of timely and appropriate

Table 4 Risk factors associated with cervical dilatationafter adjustment for confounding variables by overalllogistic regression analysis

Oddsratio

95%Confidenceinterval

P-values

Clinical CAM 0.45 0.71–2.82 0.39Frequency of

emergencycesarean section

1.39 0.43–4.57 0.24

Asphyxia neonatorum 2.27 0.27–19.37 0.45

CAM, chorioamnionitis.



medical intervention. Meanwhile, patients in group Bwho underwent cesarean section had prolonged labor;a threefold difference in the frequency of cesareansection was clinically observed between the twogroups. However, the difference was not statisticallysignificant, and we were unable to identify any clearcause, presumably due to the small number of patients.With further accumulation of cases in the future, thedifference could be reduced. On the other hand, thefrequency of forced delivery, including not only emer-gency cesarean section, but also forceps delivery andvacuum extraction, was 19.5% (17 patients) in group Aand 14.8% (four patients) in group B (P = 0.78). Themain indications for emergency cesarean section,forceps delivery and vacuum extraction were pro-longed labor and NRFS. There were no significant dif-ferences, either clinically or statistically, in the numberof deliveries requiring medical intervention.

In group A, the Bishop score improved significantlyfrom 2.5 to 6.1 following cervical dilatation with a lami-naria tent, confirming the cervix-dilatating effect oflaminaria tent insertion. However, although the Bishopscore at the beginning of labor induction was signifi-cantly higher in group A than in group B, there was nosignificant difference in the duration of labor betweenthe two groups. Laminaria tents become distended totwo- to threefold their original volume after absorbingmoisture, which results in dilatation of the uterine os.Cervical ripening is accelerated by physical extensionof the tissue and individual or mutual actions of thesubsequently induced inflammatory cytokines, such asinterleukin-8 and prostaglandins. Cervical dilatationby laminaria tent insertion may produce only weakinduction of inflammatory cytokines and prostaglan-dins or may require time to exert its action; muchremained unclear on this issue in this study. Mureanaet al. examined the effects of prostaglandin E2 givenalone and in combination with laminaria tents in caseswithout rupture of membranes in which labor wasinduced at term, and reported that the laminaria tentinsertion did not exert any synergistic effect.21 Themanifestations and effects of cytokines and prostaglan-dins may vary among different procedures of cervicaldilatation. It is of interest that the effects of cervicaldilatation may also vary for the same procedure; forexample, the effects of insertion of Foley’s cathetersvary when their volumes are different.22

Of the 87 patients in whom laminaria tent insertionwas carried out, delivery was conducted without the useof inducing agents in 10 patients. Although laminariatent insertion might have served as a trigger for the

onset of the contractions, the effect of laminaria tentinsertion remains unclear, because spontaneous con-tractions are expected to occur by 12 to 24 h after PROM.Because there was no statistically significant differencein the frequency of use of inducing agents between thetwo groups, the contraction-inducing effect of laminariatent insertion may have been only moderate.

On the other hand, the Bishop score improved to 4.9at the time of labor induction in the group B patients, inwhom labor was managed without laminaria tentinsertion. Therefore, it is presumed that membranerupture itself has a cervix-ripening effect, which mighthave accounted for the lack of a significant differencebetween the two groups in this study. Namely, in bothgroups, cervical ripening was potentially expectedafter PROM, and under this circumstance, it is difficultto discriminate the cervix-ripening effect of laminariatent insertion.

The present study was not a randomized study. Themethod of delivery management was changed at acertain point of time. However, there were no specificdifferences in the characteristics of the patient popula-tions before and after the change, with delivery man-agement parameters, except in respect of the use oflaminaria tents, remaining essentially the same. There-fore, we consider that a comparative study between thetwo populations was valid.

Although there was a concern that laminaria tentinsertion might induce infection, administration ofantimicrobial drugs to all patients with PROM mighthave prevented infection; however, we noted no caseswith clinical or pathological aggravation of CAM. Therewas no significant difference in the maternal or neona-tal outcomes between the groups in which labor wasmanaged with and without laminaria tent insertion.However, use of a laminaria tent did not reduce thetime interval from PROM to delivery, either. Moreover,there were no differences in the frequency of use oflabor-inducing or accelerating agents between the twogroups. Laminaria tent insertion is an invasive proce-dure in pregnant women that causes pain. Therefore,cervical ripening by laminaria tent insertion does notprovide any benefit for women with PROM at term.

Acknowledgments

We wish to thank Dr Tetsuji Kaneko, Dr Mari Saito andProfessor Satoshi Morita of the Department of Biosta-tistics and Epidemiology at Yokohama City UniversityMedical Center for help with performing statisticalanalysis.

K. Kurasawa et al.


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Health & Medicine

Signiﬁcance of cervical ripening in pre induction