Signiﬁcance of cervical ripening in pre induction

Significance of cervical ripening in pre-induction
treatment for premature rupture of membranes at term
Kentaro Kurasawa1
, Megumi Yamamoto1
, Yuki Usami1
, Aya Mochimaru1
,
Akihiko Mochizuki1
, Shigeru Aoki1
, Mika Okuda1
, Tsuneo Takahashi1
and
Fumiki Hirahara2
1
Perinatal Center for Maternity and Neonate, Yokohama City University Medical Center, and 2
Department of Obstetrics and
Gynecology, 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 women
with 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 with
PROM at term. Of the 486 women seen prior to 2010 (group 1), 85 had Bishop scores of 5 or less and underwent
insertion of laminaria tents (group A). In the 296 women admitted after 2010 (group 2), 27 had Bishop scores
of 5 or less and underwent labor management without insertion of laminaria tents (group B). The patient
characteristics, 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 after
laminaria 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 were
found 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 nor
contributed 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 generally
reported to occur at an incidence of approximately 8%.1
Usually, 70% and 95% of women go into labor within
24 and 72 h after PROM, respectively.2
The major
potential problem associated with PROM is ascending
infection; the incidence of infection of the mother and
fetus rises with increasing interval to labor after
PROM.3
Some advocate induction of labor, in view of the risk
of development of clinical chorioamnionitis (CAM)
while waiting for spontaneous labor, particularly in
women 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: kurasawa@yokohama-cu.ac.jp
Conflict of interest: None. We confirm that the results of this manuscript have not been distorted by research funding or conflicts
of interest.
bs_bs_banner
doi:10.1111/jog.12116 J. Obstet. Gynaecol. Res. Vol. 40, No. 1: 32–39, January 2014
32 © 2013 The Authors
Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology

pregnancy, by which time the fetus is expected to have
matured sufficiently.1,4,5
Labor can be induced by medications or by mechani-
cal cervical ripening treatments. Cervical ripening
treatments available in Japan include cervical dilatation
with hygroscopic cervical rods (e.g. Laminaria,
Dilapan, Lamicel) or with metreurynters (e.g. Mini
Metro, Foley catheter). Among the adverse events
associated with these cervical ripening treatments,
infections of the mother and fetus are of particular
importance.6–8
At present, there is no consensus as yet about the
validity of employing cervical ripening treatments for
pregnant women presenting with PROM.9
The purpose of this study was to determine whether
cervical ripening using a laminaria tent may increase
the risk of complications, including infection of the
mother and fetus, or effectively reduce the time to
delivery in women presenting with PROM at term.
Methods
Study design
In this retrospective study, we enrolled a total of 782
women with medically confirmed PROM who were
admitted to the Yokohama City University Medical
Center for labor management between September 2008
and December 2011. The subjects of this study were
women in the 37th to 41st week of a single pregnancy
with the fetus in the vertex presentation. Women
meeting the following exclusion criteria were excluded
from the study: multiple pregnancy; premature labor;
post-term delivery; malpresentation such as the pelvic
presentation; history of cesarean section; low-lying
placenta/placenta previa; uncertain due date; and
rupture of membranes during cervical ripening treat-
ment after admission for induction of labor.
At our center, we generally induce labor for women
presenting with PROM at or after 37 weeks of preg-
nancy, so as to avoid CAM and fever in the postpartum
mother. Mechanical cervical ripening treatment had
been 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 to
fail in cases with unfavorable cervical ripening, and
that cesarean section is more frequently necessary in
women 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 and
fetus. Because cervical ripening treatment in women
with ruptured membranes may increase the risk of
infection, caution is required before deciding on such
treatment. In this connection, we have been carrying
out labor management at our institute without the use
of cervical ripening treatment with laminaria tents
since October 2010. For this study, a series of 486
women with PROM who were treated between Sep-
tember 2008 and September 2010, the period during
which we performed laminaria tent insertion for unfa-
vorable cervical ripening, were classified as group 1,
and another series of women with PROM who were
admitted between October 2010 and December 2011, in
whom labor management was conducted without
laminaria tent insertion even in the presence of unfa-
vorable cervical ripening, were classified as group 2
(296 women); the two groups were compared in regard
to the patient characteristics and the perinatal out-
comes. Among the 87 women in group 1 in whom the
delivery was managed by laminaria tent insertion, 85
had Bishop scores of 5 or lower and were designated as
group A. Then, 27 women in group 2 with Bishop
scores of 5 or lower were designated as group B, and a
detailed comparison of the characteristics was con-
ducted between group A and group B. The primary
outcome was determination of the presence/absence of
influence of laminaria tent insertion on the risk of
infection in the mother and fetus. The secondary
outcome was determination of the influence of lami-
naria tent insertion on the time interval from PROM to
delivery, to effectively avoid the risk of infection.
Induction protocol
When there was no obvious fluid escaping from the
cervix, a diagnosis of PROM was made by the nitrazine
test using the Amnicator. Women who were diagnosed
as having PROM were hospitalized, and all were given
antimicrobial drug therapy. At our center, women who
come to the outpatient clinic at 36 weeks of pregnancy
are basically subjected to swab cultures of the lower
vagina and of the perianal region to screen for group B
Streptococci (GBS). In this study, patients who were
positive for GBS were given an i.v. drip infusion of 2 g
aminobenzyl penicillin (ABPC) after admission, fol-
lowed by administration of 1 g ABPC every 4 h until
the end of delivery. There was no case of penicillin
allergy. Patients who were negative for GBS were given
an oral 100-mg tablet of cefcapene pivoxil after every
meal until the end of delivery.
Fetal cardiotocograms were evaluated immediately
after 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 33

uterine tenderness, blood biochemical data and other
evaluations were carried out.
In group 1, patients who were diagnosed as having
low Bishop scores by the attending obstetrician under-
went laminaria tent insertion and were observed over-
night. Approximately 12 h later, namely, the following
morning, the laminaria tents were removed and deliv-
ery was induced. The attending obstetrician selected
oxytocin or prostaglandin F2a as the inducing agent, at
his/her discretion. Administration of oxytocin was
begun at an initial dose of 2 mIU/min, with the dose
increased by 2 mIU/min at intervals of at least 40 min,
while ensuring that the final dose did not exceed
20 mIU/min. Administration of prostaglandin F2a was
begun at a dose of 1.5 mg/min, with the dose increased
by 1.5 mg/min at intervals of at least 30 min, while
ensuring 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 of
labor.
In group 2, patients were observed overnight,
regardless of the Bishop scores. On the following
morning, labor was induced in patients who did not
have spontaneous contractions. The same method
and dose for labor induction were used as those for
group A.
The diagnosis of intrauterine infection was made
based on a minor modification of the definition of clini-
cal CAM proposed by Lencki et al.10
In mothers with
fever (Ն38.0°C), fulfillment of at least one of the fol-
lowing criteria was necessary, while in mothers
without fever, fulfillment of at least three of the follow-
ing criteria was necessary: (i) maternal tachycardia; (ii)
uterine tenderness; (iii) vaginal discharge/a foul odor
of the amniotic fluid; and (iv) leukocytosis (Ն15 000/
mm3
). According to the definition by Lencki et al., all
the above four criteria needed to be fulfilled in mothers
without fever. However, it is common for uterine
infection to be clinically established by the time all four
criteria are fulfilled,11–13
and medical interventions,
including pregnancy termination, are often performed
before this stage. Therefore, at our center, we deter-
mined that fulfillment of only three of the criteria was
sufficient for the diagnosis.
The present study was conducted with the approval
of the Ethics Review Committee of our center (Yoko-
hama City University Medical Center Ethics Review
Committee Approval Number: D1203001).
Statistical analysis
We compared the two groups in terms of continuous
variables not showing normal distribution by Mann–
Whitney U-test and categorical data by the c2
-test. The
odds ratios were calculated to assess the risk of lami-
naria tent insertion in the patients with a Bishop score
of 5 or lower. Post-hoc power was also calculated based
on the observed effect and sample size. Significance
level was set at P < 0.05. IBM SPSS statistics ver. 19.0 for
Windows was used for the statistical analyses.
Results
Among the 782 patients with PROM at term included
in this study, the 486 women in group 1 were treated
during the period when deliveries were managed at
our center with cervical ripening by laminaria tent
insertion, whereas the 296 women in group 2 were
treated after we established a rule to manage deliveries
without cervical ripening using laminaria tents. Table 1
shows the characteristics of the patients in this study.
There were no significant differences in the maternal
age, 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 Ϯ 5.0 32.8 Ϯ 5.6 0.12
Percentage of nulliparas 314 (64.6%) 200 (67.6%) 0.40
Gestational age at delivery 39.4 Ϯ 1.1 39.4 Ϯ 1.0 0.32
BMI at 1st trimester 21.3 Ϯ 3.4 21.1 Ϯ 3.1 0.56
BMI at delivery 25.2 Ϯ 3.3 25.1 Ϯ 3.1 0.85
Bishop scores 4.7 Ϯ 2.3 5.0 Ϯ 2.2 0.33
Body temperature (°C) 36.6 Ϯ 0.39 36.5 Ϯ 0.46 0.01
Fetal heart rate (b.p.m.) 136.6 Ϯ 9.6 135.6 Ϯ 10.3 0.13
Values are given as mean Ϯ standard deviation or number (percentage). BMI, body mass
index.
K. Kurasawa et al.

delivery, Bishop score at admission or the fetal heart
rate 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 both
groups, this difference might have been of little clinical
significance.
Table 2 shows the overall delivery course and the
neonatal outcomes. In group 1, 87 patients underwent
cervical dilatation by laminaria tent insertion. More
than half of the patients in both groups were delivered
without the use of inducing agents. There was no sig-
nificant difference in the frequency of use of inducing
agents between the two groups. In addition, there were
no significant intergroup differences in the interval
from PROM to delivery or the interval from the begin-
ning of labor pain to the end of delivery between the
two groups. Moreover, no significant differences were
found in regard to the frequencies of non-reassuring
fetal status (NRFS), meconium staining of amniotic
fluid, clinical CAM or emergency cesarean section
between the two groups. The Bishop score on admis-
sion was 4.7 Ϯ 1.1 in group 1 and 5.0 Ϯ 2.2 in group 2,
the difference not being statistically significant. In
regard to the neonatal outcomes, no significant differ-
ences were found between the two groups in terms of
the neonatal bodyweight, Apgar score, frequency of
asphyxia neonatorum or umbilical artery pH (UApH).
In addition, pathological CAM was diagnosed in 27
patients (CAM grade 1 in 10, CAM grade 2 in seven
and CAM grade 3 in 10 patients) of group 1 and in 15
patients (CAM grade 1 in eight, CAM grade 2 in three
and CAM grade 3 in four patients) of group 2, with no
statistically significant intergroup differences.
Table 3 shows the maternal characteristics, delivery
course and neonatal outcomes in patients who showed
unfavorable cervical ripening, with Bishop scores of 5
or lower. In group A, 85 patients had Bishop scores of
5 or lower and underwent laminaria tent insertion,
whereas in group B, 27 patients had similarly low
Bishop scores. In comparison to that in patients with
ruptured membranes as a whole, the percentage of
nulliparas was clearly higher, and the time interval
from PROM to delivery was longer in these subgroups
of patients with low Bishop scores. In group A, the
Bishop score at the time of PROM was 2.5 Ϯ 1.5,
improving significantly after laminaria tent insertion to
6.1 Ϯ 2.4. The Bishop score at the time of labor induc-
tion was significantly higher in group A than in group
B (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 B
than in group A (P < 0.01). The inducing agents used in
the 85 patients in group A were oxytocin in 60, pros-
taglandin F2a in five, and oxytocin and prostaglandin
F2a in 12 patients. In the 22 patients in group B, oxy-
tocin was used in 14 (51.9%), prostaglandin F2a in
eight (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 <0.01
Frequency of use of inducing agents 204 (46%) 121 (40.9%) 0.76
Changes in Bishop score (in ~12 h) 2.2 1.8 0.77
Duration of labor (h) 6.0 (0.6–42.6) 6.7 (0.6–52.9) 0.68
Time from rupture to delivery (h) 19.6 (1.1–101.9) 17.1 (0.5–88.7) 0.18
Frequency of emergency cesarean section 29 (6.5%) 15 (5.1%) 0.60
NRFS 52 (10.7%) 40 (13.5%) 0.24
Frequency of meconium staining 74 (15.2%) 47 (15.9%) 0.81
Clinical CAM 10 (2.1%) 13 (4.4%) 0.06
Amount of bleeding at delivery (g) 349 (58–2062) 385 (51–2112) 0.07
Neonatal body weight (g) 3006 Ϯ 371 2992 Ϯ 348 0.62
UApH 7.28 Ϯ 0.65 7.27 Ϯ 0.88 0.37
APS (1) 8.4 Ϯ 1.0 8.3 Ϯ 1.2 0.23
APS (5) 9.2 Ϯ 0.6 9.1 Ϯ 0.8 0.09
Asphyxia Neonatorum 17 (3.5%) 11 (3.7%) 0.87
Histological CAM 27/56 (48.2%) 15/32 (46.8%) 0.52
Values are given as mean Ϯ 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 two
agents were not used concomitantly. There were no
significant differences in the duration of labor or the
time interval from PROM to delivery between the two
groups. Forced delivery as a whole, including forceps
delivery and vacuum extraction, was required in 17
patients (19.5%) of group A and four (14.8%) of group
B, with no statistically significant difference in the per-
centage of deliveries requiring medical intervention
between the two groups (P = 0.78). Although the fre-
quencies of emergency cesarean section, clinical CAM
and asphyxia neonatorum differed by three-, two- and
twofold, respectively, there were no statistically signifi-
cant differences in the frequencies of NRFS, meconium
staining of the amniotic fluid, clinical CAM or emer-
gency cesarean section between the two groups. The
frequencies of NRFS and meconium staining of the
amniotic fluid were similar; however, there were three
patients with both NRFS and meconium staining of the
amniotic fluid in group A and one in group B. In regard
of the neonatal outcomes, there were no significant
intergroup differences in the neonatal bodyweight,
Apgar score, frequency of asphyxia neonatorum or
UApH. Pathological CAM was found in six patients in
group A and four patients in group B. The risks of
adverse events associated with laminaria tent insertion
are shown in Table 4. The odds ratios were 0.45 for
clinical CAM (95% confidence interval [CI], 0.07–2.82),
1.39 for cesarean section (95% CI, 0.43–4.57) and 2.27
for 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 the
sample size and parameter estimates derived from the
given data. The post-hoc power values of cesarean
section, clinical CAM and asphyxia neonatorum were
18.3%, 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 Ϯ 4.9 33.4 Ϯ 5.0 0.37
Percentage of nulliparas 75 (86.2%) 22 (85.1%) 0.54
Gestational age at delivery (weeks) 39.7 Ϯ 1.1 39.5 Ϯ 1.0 0.43
BMI before pregnancy 22.1 Ϯ 3.8 21.7 Ϯ 2.7 0.62
BMI at delivery 26.1 Ϯ 3.6 26.1 Ϯ 2.5 0.99
Bishop score (at admission) 2.5 Ϯ 1.5 2.6 Ϯ 0.8 0.74
Bishop score (12–18 h later) 6.1 Ϯ 2.4 4.9 Ϯ 2.4 0.03
Frequency of use of inducing agents 77 (88.5%) 27 (100%) 0.17
Duration of labor 6.9 (0.9–28.2) 6.0 (1.0–13.8) 0.21
Time from rupture to delivery 35.2 (5.1–101.9) 39.1 (3.0–77.8) 0.49
Total amount of bleeding (g) 408 (58–1935) 567 (120–1596) 0.41
Body temperature (°C) (on admission) 36.5 Ϯ 0.34 36.5 Ϯ 0.41 0.72
Body temperature (°C) (following morning) 36.9 Ϯ 0.37 36.7 Ϯ 0.27 0.24
Fetal heart rate (b.p.m.) (on admission) 139.0 Ϯ 6.4 133.3 Ϯ 10.2 0.04
CRP (on admission) 0.67 Ϯ 0.78 0.54 Ϯ 0.46 0.48
Forced delivery 17 (19.5%) 4 (14.8%) 0.78
Frequency of emergency cesarean section 11 (12.6%) 1 (3.7%) 0.18
NRFS 15 (17.2%) 3 (11.1%) 0.45
Frequency of meconium staining 15 (17.2%) 3 (11.1%) 0.45
Clinical CAM 3 (3.4%) 2 (7.4%) 0.38
Neonatal body weight (g) 2995 Ϯ 377 2969 Ϯ 351 0.76
APS (1) 8.05 Ϯ 1.52 8.15 Ϯ 1.43 0.76
APS (5) 9.10 Ϯ 0.65 9.00 Ϯ 1.00 0.53
UApH 7.28 Ϯ 0.06 7.27 Ϯ 0.07 0.54
Asphyxia neonatorum 7 (8.0%) 1 (3.7%) 0.44
Pathological CAM (I–III) 6/11 4/6 0.63
CAM I 2 0
CAM II 1 1
CAM III 3 3
Admission to NICU 12 (13.8%) 5 (18.5%) 0.55
Values are given as mean Ϯ 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 dilatation
by laminaria tent insertion in women presenting with
PROM at term was not associated with any increase in
the incidence of intrauterine infection and pathological
CAM or in the mode of delivery. There was also no
reduction in the duration of labor or the time interval
from PROM to delivery.
The benefits expected from mechanical cervical dila-
tation using laminaria tents or other means include
facilitation of cervical ripening and early completion of
delivery. It also has the advantage of being less likely to
be associated with excessive contractions.14
It has been
reported that the failure rate of induction and accelera-
tion of contractions are higher in patients with
extremely unfavorable cervical ripening.15,16
In North
America and other countries overseas, prostaglandin
E2 gel, designed for direct application to the cervical
canal of the uterus, is used frequently.17,18
In contrast,
manual membrane sweep and mechanical cervical
dilatation using laminaria tents are commonly used in
Japan. Although it has been reported that cervical dila-
tation itself increases the risk of infection in patients
with ruptured membranes,6–8
this remains to be veri-
fied. Therefore, the 2011 edition of the guidelines for
obstetrical practice in Japan has approved the use of
mechanical cervical dilatation, with due caution paid to
the risk of infection.9
PROM at term has recently been
suggested to be correlated with abnormalities in the
central nervous system of the fetus, in addition to
being associated with an increased risk of intrauterine
infection.12,13
Because the fetus may be considered to
have matured sufficiently by term, early completion of
delivery should be aimed for. However, there is the
paradox 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 observed
without induction, and found that the incidence of
CAM 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 cesarean
section or mechanical vaginal delivery between the two
groups. Thus, they concluded that induction of labor
was an effective medical intervention.
In our study, there was also no decrease in the inci-
dence of CAM or the rate of NICU admission. These
findings may be primarily explained by our use of
antimicrobial medications in all the patients, although
it remains controversial whether antimicrobial drugs
should be given to all patients with PROM at term.6
The use of antimicrobial medications might have
delayed the onset of intrauterine infection in our
patients. Although it has been reported that the time
interval from PROM to onset of intrauterine infection
is approximately 12–16 h,3
it is known that the risk of
infection increases as this time interval increases. In
our study, the mean time interval from PROM to
delivery was 36 h. The fact that delivery occurred
within 2 days after PROM under antimicrobial
therapy seems to explain the lack of the difference in
the 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 of
CAM, and the use of antimicrobial drugs in this study
might have played an important role. Second, it is
speculated that appropriate medical intervention was
provided 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 a
clinical diagnosis of CAM can be made. It is known
that the diagnosis of clinical CAM is associated with a
significant increase in the incidence of neonatal sepsis
and significantly increased risk of chronic lung
disease, cerebral palsy, and periventricular leukoma-
lacia related to fetal inflammatory reaction syndrome
caused by hypercytokinemia.11–13,20
The indication for the cesarean section in these 11
patients was NRFS (n = 6), prolonged labor (n = 4) or
maternal indication (hypertension; n = 1). One of the
patients with prolonged labor had a mild fever of
37.2°C and was judged to have signs of maternal infec-
tion, although she did not meet Lencki’s diagnostic
criteria for clinical CAM. It is considered that a clear-
cut diagnosis of clinical CAM in this patient was
avoided by provision of timely and appropriate
Table 4 Risk factors associated with cervical dilatation
after adjustment for confounding variables by overall
logistic regression analysis
Odds
ratio
95%
Confidence
interval
P-values
Clinical CAM 0.45 0.71–2.82 0.39
Frequency of
emergency
cesarean 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 B
who underwent cesarean section had prolonged labor;
a threefold difference in the frequency of cesarean
section was clinically observed between the two
groups. However, the difference was not statistically
significant, and we were unable to identify any clear
cause, presumably due to the small number of patients.
With further accumulation of cases in the future, the
difference could be reduced. On the other hand, the
frequency of forced delivery, including not only emer-
gency cesarean section, but also forceps delivery and
vacuum extraction, was 19.5% (17 patients) in group A
and 14.8% (four patients) in group B (P = 0.78). The
main 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 number
of deliveries requiring medical intervention.
In group A, the Bishop score improved significantly
from 2.5 to 6.1 following cervical dilatation with a lami-
naria tent, confirming the cervix-dilatating effect of
laminaria tent insertion. However, although the Bishop
score at the beginning of labor induction was signifi-
cantly higher in group A than in group B, there was no
significant difference in the duration of labor between
the two groups. Laminaria tents become distended to
two- to threefold their original volume after absorbing
moisture, which results in dilatation of the uterine os.
Cervical ripening is accelerated by physical extension
of the tissue and individual or mutual actions of the
subsequently induced inflammatory cytokines, such as
interleukin-8 and prostaglandins. Cervical dilatation
by laminaria tent insertion may produce only weak
induction of inflammatory cytokines and prostaglan-
dins or may require time to exert its action; much
remained unclear on this issue in this study. Mureana
et al. examined the effects of prostaglandin E2 given
alone and in combination with laminaria tents in cases
without rupture of membranes in which labor was
induced at term, and reported that the laminaria tent
insertion did not exert any synergistic effect.21
The
manifestations and effects of cytokines and prostaglan-
dins may vary among different procedures of cervical
dilatation. It is of interest that the effects of cervical
dilatation may also vary for the same procedure; for
example, the effects of insertion of Foley’s catheters
vary when their volumes are different.22
Of the 87 patients in whom laminaria tent insertion
was carried out, delivery was conducted without the use
of inducing agents in 10 patients. Although laminaria
tent insertion might have served as a trigger for the
onset of the contractions, the effect of laminaria tent
insertion remains unclear, because spontaneous con-
tractions are expected to occur by 12 to 24 h after PROM.
Because there was no statistically significant difference
in the frequency of use of inducing agents between the
two groups, the contraction-inducing effect of laminaria
tent insertion may have been only moderate.
On the other hand, the Bishop score improved to 4.9
at the time of labor induction in the group B patients, in
whom labor was managed without laminaria tent
insertion. Therefore, it is presumed that membrane
rupture itself has a cervix-ripening effect, which might
have accounted for the lack of a significant difference
between the two groups in this study. Namely, in both
groups, cervical ripening was potentially expected
after PROM, and under this circumstance, it is difficult
to discriminate the cervix-ripening effect of laminaria
tent insertion.
The present study was not a randomized study. The
method of delivery management was changed at a
certain point of time. However, there were no specific
differences in the characteristics of the patient popula-
tions before and after the change, with delivery man-
agement parameters, except in respect of the use of
laminaria tents, remaining essentially the same. There-
fore, we consider that a comparative study between the
two populations was valid.
Although there was a concern that laminaria tent
insertion might induce infection, administration of
antimicrobial drugs to all patients with PROM might
have prevented infection; however, we noted no cases
with clinical or pathological aggravation of CAM. There
was no significant difference in the maternal or neona-
tal outcomes between the groups in which labor was
managed with and without laminaria tent insertion.
However, use of a laminaria tent did not reduce the
time interval from PROM to delivery, either. Moreover,
there were no differences in the frequency of use of
labor-inducing or accelerating agents between the two
groups. Laminaria tent insertion is an invasive proce-
dure in pregnant women that causes pain. Therefore,
cervical ripening by laminaria tent insertion does not
provide any benefit for women with PROM at term.
Acknowledgments
We wish to thank Dr Tetsuji Kaneko, Dr Mari Saito and
Professor Satoshi Morita of the Department of Biosta-
tistics and Epidemiology at Yokohama City University
Medical Center for help with performing statistical
analysis.
K. Kurasawa et al.

References
1. ACOG Practice Bulletin No. 80: premature rupture of mem-
branes. Clinical management guidelines for obstetrician-
gynecologists. Obstet Gynecol 2007; 109: 1007–1019.
2. Hannah ME, Ohlsson A, Farine D et al. Induction of labor
compared with expectant management for prelabor rupture
of the membranes at term. TERMPROM Study Group. N Engl
J Med 1996; 334: 1005–1010.
3. Tran SH, Cheng YW, Kaimal AJ, Caughey AB. Length of
rupture of membranes in the setting of premature rupture of
membranes at term and infectious maternal morbidity. Am J
Obstet Gynecol 2008; 198: 700e1–700e5.
4. Mercer BM, Crocker LG, Boe NM, Sibai BM. Induction versus
expectant management in premature rupture of the mem-
branes with mature amniotic fluid at 32 to 36 weeks: A ran-
domized trial. Am J Obstet Gynecol 1993; 169: 775–782.
5. Dare MR, Middleton P, Crowther CA, Flenady V, Varatharaju
B. Planned early birth versus expectant management
(waiting) for prelabour rupture of membranes at term (37
weeks or more) (Review). Cochrane Database Syst Rev 2009;
(1): CD005302.
6. Heinemann J, Gillen G, Sanchez-Ramos L, Kaunitz AM. Do
mechanical methods of cervical ripening increase infectious
morbidity? A systematic review. Am J Obstet Gynecol 2008;
199: 177–187. discussion 87–8.
7. Krammer J, Williams MC, Sawai SK, O’Brien WF. Pre-
induction cervical ripening: A randomized comparison of
two methods. Obstet Gynecol 1995; 85: 614–618.
8. Kazzi GM, Bottoms SF, Rosen MG. Efficacy and safety of
Laminaria digitata for preinduction ripening of the cervix.
Obstet Gynecol 1982; 60: 440–443.
9. Minakami H, Hiramatsu Y, Koresawa M et al. Guidelines for
obstetrical practice in Japan: Japan Society of Obstetrics and
Gynecology (JSOG) and Japan Association of Obstetricians
and Gynecologists (JAOG) 2011 edition. J Obstet Gynaecol Res
2011; 37: 1174–1197.
10. Lencki SG, Maciulla MB, Eglinton GS. Maternal and umbili-
cal cord serum interleukin levels in preterm labor with clini-
cal chorioamnionitis. Am J Obstet Gynecol 1994; 170: 1345–
1351.
11. Lieberman E, Lang J, Richardson DK, Frigoletto FD, Heffner
LJ, Cohen A. Intrapartum maternal fever and neonatal
outcome. Pediatrics 2000; 105: 8–13.
12. Yoon BH, Park CW, Chaiworapongsa T. Intrauterine infection
and the development of cerebral palsy. BJOG 2003; 110
(Suppl 20): 124–127.
13. Shatrov JG, Birch SC, Lam LT, Quinlivan JA, McIntyre S,
Mendz GL. Chorioamnionitis and cerebral palsy: A meta-
analysis. Obstet Gynecol 2010; 116: 387–392.
14. Jozwiak M, Bloemenkamp KW, Kelly AJ, Mol BW, Irion O,
Boulvain M. Mechanical methods for induction of labour.
Cochrane Database Syst Rev 2012; (3): CD001233.
15. Vrouenraets FP, Roumen FJ, Dehing CJ, van den Akker ES,
Aarts MJ, Scheve EJ. Bishop score and risk of cesarean deliv-
ery after induction of labor in nulliparous women. Obstet
Gynecol 2005; 105: 690–697.
16. Park KH, Hong JS, Ko JK et al. Comparative study of induc-
tion of labor in nulliparous women with premature rupture
of membranes at term compared to those with intact mem-
branes: Duration of labor and mode of delivery. J Obstet
Gynaecol Res 2006; 32: 482–488.
17. Chaudhuri S, Mitra SN, Banerjee PK, Biswas PK, Bhatta-
charyya S. Comparison of vaginal misoprostol tablets
and prostaglandin E2 gel for the induction of labor in
premature rupture of membranes at term: A randomized
comparative trial. J Obstet Gynaecol Res 2011; 37: 1564–
1571.
18. Herabutya Y, O-Prasertsawat P, Pokpirom J. A comparison of
intravaginal misoprostol and intracervical prostaglandin E2
gel for ripening of unfavorable cervix and labor induction.
J Obstet Gynaecol Res 1997; 23: 369–374.
19. Flenady V, King JF. Antibiotics for prelabour rupture of
membranes at or near term (Review). Cochrane Database Syst
Rev 2012; (3): CD001807.
20. Sato M, Nishimaki S, Yokota S et al. Severity of chorioam-
nionitis and neonatal outcome. J Obstet Gynaecol Res 2011; 37:
1313–1319.
21. Turnquest MA, Lemke MD, Brown HL. Cervical ripening:
Randomized comparison of intravaginal prostaglandin E2 gel
with prostaglandin E2 gel plus laminaria tents. J Matern Fetal
Med 1997; 6: 260–263.
22. Delaney S, Shaffer BL, Cheng YW et al. Labor induction with
a Foley balloon inflated to 30 mL compared with 60 mL: A
randomized controlled trial. Obstet Gynecol 2010; 115: 1239–
1245.

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