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Significance of cervical ripening in pre induction

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  • 1. 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
  • 2. 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 Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology
  • 3. 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. 34 © 2013 The Authors Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology
  • 4. 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. Pre-induction treatment for PROM at term © 2013 The Authors 35 Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology
  • 5. 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. 36 © 2013 The Authors Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology
  • 6. 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. Pre-induction treatment for PROM at term © 2013 The Authors 37 Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology
  • 7. 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. 38 © 2013 The Authors Journal of Obstetrics and Gynaecology Research © 2013 Japan Society of Obstetrics and Gynecology
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