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ORIGINAL ARTICLE
Year : 2021  |  Volume : 5  |  Issue : 3  |  Page : 148-153

Impact of early versus late amniotomy on induction of labor in nulliparous women after vaginally administered misoprostol: A randomized clinical trial


Department of Obstetrics and Gynecology, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission26-Oct-2020
Date of Decision07-Jan-2021
Date of Acceptance22-Apr-2021
Date of Web Publication21-Aug-2021

Correspondence Address:
Mohamed Elsibai Anter
Department of Obstetrics and Gynecology, Faculty of Medicine, Menoufia University, Menoufia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2096-2924.324223

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  Abstract 


Objective: To investigate the effect of early versus late amniotomy after induction of labor (IOL) with vaginally administered misoprostol.
Methods: This randomized clinical trial was conducted at the Department of Obstetrics and Gynecology, Menoufia University, from May 2019 to March 2020, and included 120 nulliparous women at term (≥ 37 weeks' gestation) undergoing IOL. Computer-generated randomization was used to randomize the participants into either the early amniotomy group (3 cm cervical dilatation; n = 60) or the late amniotomy group (7 cm cervical dilatation; n = 60). All participants received misoprostol (25 μg) vaginally to induce labor. The primary outcome was the induction-to-delivery interval, defined as the time from the initiation of IOL to the time of delivery.
Results: Women in the early amniotomy group had a shorter duration of labor (12.60 ± 5.36 h) than those in the late amniotomy group (16.67 ± 7.26 h). The mean time from rupture of the fetal membrane to delivery was significantly shorter in the late (2.51 ± 0.36 h) than in the early amniotomy group (3.1 ± 0.89 h). There was no statistically significant difference between the groups in terms of maternal complications (fever, nausea, vomiting, and uterine hyperstimulation) or neonatal complications (meconium-stained liquor, APGAR score <7 at 1 and 5 min, and neonatal intensive care unit admission).
Conclusions: IOL using vaginally administered misoprostol followed by early amniotomy was accompanied by a shorter duration of labor and decreased use of oxytocin. There was no significant difference between the early and late amniotomy groups in terms of the rate of cesarean section or maternal and neonatal complications.

Keywords: Amniotomy; Induction of Labor; Neonatal Outcomes; Vaginal Misoprostol


How to cite this article:
Anter ME, Elkader Shabbana AA, Fatahlla Elhalaby AE, Abd Elfattah Youssif HA, Elkhouly NI. Impact of early versus late amniotomy on induction of labor in nulliparous women after vaginally administered misoprostol: A randomized clinical trial. Reprod Dev Med 2021;5:148-53

How to cite this URL:
Anter ME, Elkader Shabbana AA, Fatahlla Elhalaby AE, Abd Elfattah Youssif HA, Elkhouly NI. Impact of early versus late amniotomy on induction of labor in nulliparous women after vaginally administered misoprostol: A randomized clinical trial. Reprod Dev Med [serial online] 2021 [cited 2021 Dec 8];5:148-53. Available from: https://www.repdevmed.org/text.asp?2021/5/3/148/324223




  Introduction Top


Induction of labor (IOL) is employed when the advantages of terminating a pregnancy outweigh those of continuing the pregnancy. However, there is a positive association between IOL and the rate of cesarean section (CS).[1] Risk factors for CS during IOL include nulliparity, increased birth weight, and the use of cervical ripening agents.[2] Early amniotomy is defined as the artificial rupture of membrane (ROM) before the active phase of labor, and late amniotomy is defined as the artificial ROM after the onset of the active phase of labor. Amniotomy promotes the release of mediators such as oxytocin and prostaglandins, which accelerate labor and expedite delivery for both spontaneous and induced labor.[3] Early spontaneous ROM is associated with a high rate of CS in nulliparous women in spontaneous labor, possibly because early ROM is more likely to occur in women with cephalopelvic disproportion.[4] The use of misoprostol to ripen the cervix (induce labor) is accompanied by an overall lower incidence of CS, a higher incidence of normal vaginal delivery (within 24 h of application), and a decrease in the use of oxytocin augmentation.[5] Vaginally administered misoprostol has a quicker delivery with less hyperstimulation and tachysystole than oral administration.[6] Although many reports have provided evidence that labor induction methods have improved,[7],[8] there is a critical need for additional tools to refine the practice of induction.

Amniotomy has been evaluated in the context of spontaneous labor; however, clear guidelines have not been issued.[9] Amniotomy combined with oxytocin infusion is commonly used during IOL; however, there is a lack of data on the effectiveness and ideal timing of this procedure.[10] Many studies have compared early versus late amniotomy in IOL, with marked variations in outcomes, including shorter labor, lower risk of chorioamnionitis, and reduced rate of CS for dystocia. Although the importance of amniotomy in spontaneous labor has been assessed in previous studies, surprisingly, few previous trials have focused on the importance of early amniotomy in the context of IOL.[11] Furthermore, to the best of our knowledge, no randomized controlled study has evaluated amniotomies performed after the vaginal delivery of misoprostol for IOL. We hypothesized that early amniotomy after vaginal delivery of misoprostol for cervical ripening would be more effective at inducing labor than that after the administration of oxytocin. This study aimed to evaluate the effect of the timing of amniotomy (early vs. late) after vaginal administration of misoprostol in induced labor.


  Patients and Methods Top


Study setting

This randomized clinical trial was conducted at the Department of Obstetrics and Gynecology from May 2019 to March 2020. Of the 140 potential cases, 120 women met the inclusion criteria (20 cases were excluded; 7 declined consent and 13 did not meet the inclusion criteria) [Figure 1]. The eligible population included pregnant women with a live singleton fetus at term (≥ 37 weeks' gestation) undergoing IOL for any reason (e.g., intrauterine fetal growth restriction, postterm pregnancy, and preeclampsia). The exclusion criteria were as follows: macrosomic babies with an estimated fetal weight > 4, 000 g, previous uterine scars, premature ROMs, and polyhydramnios.
Figure 1: CONSORT flowchart.

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Participants

Pregnant women were randomly and equally assigned to two groups: the early amniotomy group (n = 60), who underwent amniotomy at 3 cm cervical dilatation with Kocher's forceps provided the head was well-positioned in the cervix, and the late amniotomy group (n = 60), who underwent amniotomy at 7 cm cervical dilatation. The computer-generated randomization method was used, and allocation was performed using consecutively numbered, sealed, opaque envelopes.

Data collection

All participants presented to the Department of Obstetrics and Gynecology, where they provided a full personal and medical history and underwent both general and abdominal examinations. Gestational age was determined according to the date of the last menstrual period or first-trimester crown-rump length measurement on ultrasound. Body mass index (BMI) was calculated (weight [kg]/height [m2]) before delivery.

Examination

Obstetric ultrasonography and local vaginal examinations were performed to determine the presentation and position. The participants' pre-induction cervical status was evaluated according to the Bishop's score. Preinduction fetal heart rate monitoring using continuous cardiotocography was conducted to evaluate fetal well-being. Participants were included when the fetal heart rate trace was reassuring. Continued fetal monitoring was performed after the start of uterine contractions.

Monitoring labor

The pregnant women were administered 25 μg of misoprostol vaginally (Vagiprost vaginal tablet; Adwia Pharmaceutical Company, Egypt) every 6 h until there were ≥ 3 uterine contractions lasting 40 s over a 10-min period or until four doses were administered (i.e., 100 μg). Labor progress was assessed using a partogram and continuous cardiotocography to monitor both the mother and fetus. If there was no progress in labor by 6 h from the last dose of misoprostol, a failed induction was documented, and a CS was performed. Successful IOL was defined as vaginal delivery within 24 h of misoprostol administration. The augmentation of labor was performed with oxytocin in women with a cervical dilation of 4 cm or more with unsatisfactory progress of labor (arrest of cervical dilatation for ≥ 2 h and/or inadequate uterine activity) 6 h after the last prostaglandin dose in the induction regimen.

Outcomes

The primary outcome of this study was the induction-to-delivery interval, defined as the time from initiation of induction to the time of delivery. Secondary outcomes were the induction-to-amniotomy interval (the time from initiation of induction to the time of amniotomy), the amniotomy-to-delivery interval (the time from amniotomy to the time of delivery), successful induction (defined as vaginal delivery within 24 h of the initiation of induction), number of misoprostol doses administered, need for augmentation with oxytocin, fetal complications (meconium-stained liquor, APGAR score < 7 at 1 and 5 min, or newborn admission to the neonatal intensive care unit [NICU]), and maternal complications (maternal fever, nausea, vomiting, or uterine hyperstimulation).

Power analysis

A statistical power analysis was performed after the sample size was estimated based on data from the current study (n = 120), distributed into two groups. The effect size for the induction-to-delivery interval was 0.63, which was considered to be large using Cohen's (1988) criteria, with an alpha of 0.05 and sample size of 120. With 60 participants in each group, a post hoc power analysis was conducted with this effect size (G Power 3.1), which was approximately 0.93 (1− β). Thus, the power analysis showed that this sample size was adequate for the main objective of this study, while also allowing for expected attrition and our additional objectives of controlling for possible mediating/moderating factors and the subgroup analysis.

Ethical approval

This study was approved by the local ethics committee (No. 11/2019OBSGN27), and the study protocol was registered at ClinicalTrials.gov (identifier: NCT04514770). Women who agreed to participate provided signed informed consent after an explanation of the benefits and risks of participating in the trial. All procedures were carried out in accordance with the ethical standards of the institutional and national research committees and with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.

Statistical analysis

The results were analyzed using SPSS (version 22; SPSS Inc., Chicago, IL, USA). The test of normality was performed, and an unpaired t-test was used to compare the two means of normally distributed data, while the Mann–Whitney U-test was used for non-normally distributed data. The Chi-square (χ2) test was used for qualitative variables. The Fisher's exact test was used instead of χ2 test when the expected count was <5 for any of the cells. A P < 0.05 was considered statistically significant.


  Results Top


No statistically significant differences were observed between the groups in terms of mean age, mean gestational age, BMI, or mean pre-induction Bishop score (P > 0.05) [Table 1]. There were statistically significant differences between the groups in terms of the method of induction delivery, induction-to-amniotomy interval, and amniotomy-to-delivery interval (P < 0.001). Women in the early amniotomy group had a shorter duration of labor (12.60 ± 5.36 h) than those in the late amniotomy group (16.67 ± 7.26 h). The mean amniotomy-to-delivery interval was significantly shorter in the late (2.51 ± 0.36 h) than in the early amniotomy group (3.10 ± 0.89 h) [Table 2]. No statistically significant differences were found between the two groups in terms of the indication for induction, need for oxytocin, and mode of delivery (P > 0.05). However, the number of doses of misoprostol was significantly different between the groups (early amniotomy group: 15 cases [25.0%] delivered after one dose, 36 cases [60.0%] delivered after 2 doses, and 9 cases [15.0%] delivered after 3 doses; late amniotomy group: 3 cases [5.0%] delivered after one dose, 35 cases [58.3%] delivered after 2 doses, 20 cases [33.3%] delivered after 3 doses, and two cases [3.3%] required 4 doses) [Table 3]. No statistically significant differences in maternal complications (fever, nausea, vomiting, and uterine hyperstimulation) or neonatal complications (meconium-stained liquor, APGAR score < 7 at 1 and 5 min, and need for NICU admission) were present between the groups (P > 0.05) [Table 4].
Table 1: Demographic data of the study groups

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Table 2: Comparison of induction-related indicators between the study groups

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Table 3: Clinical outcomes of labor induction between the study groups

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Table 4: Comparison of fetal and maternal complications between the study groups

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  Discussion Top


There were no statistically significant differences between the groups in terms of demographic data (mean age, mean gestational age, BMI, and the mean pre-induction Bishop score) in our study. In addition, the need for CS was lower in the early than in the late amniotomy group (13 vs. 19). More subjects achieved vaginal delivery within 24 h in the early than in the late amniotomy group.

Our results were consistent with those of the study conducted by Wei et al., which concluded that early amniotomy had a lower incidence of CS than standard care (risk ratio [RR], 0.89; 95% confidence interval [CI] 0.79–1.01).[12] Another study conducted by Macones et al. found no difference between early and late amniotomy in terms of CS rate during IOL (68% vs. 56%).[13] In addition, Smyth et al. found no increase in the CS rate among women who underwent amniotomy (RR, 1.27; 95% CI 0.99–1.62).[9] However, this finding was not consistent with that of the study conducted by Lee et al., which showed that early amniotomy was associated with an increased risk of CS delivery in induced labor (24% vs. 10%; P < 0.01), which was explained by the relationship between unfavorable cervical dilation and increased incidence of CS.[14]

In induced labor, a relatively unripe cervix at the start of induction may contribute to cephalopelvic disproportion during labor progression and inadequate descent of the fetal head. In addition, Lee et al. and Cunningham and Williams found a higher rate of CS in early than in late amniotomy (18% vs. 8%, P < 0.01) and concluded that after ROM, the absence of hydrostatic pressure of the membranes may result in slow progress of labor and a correspondingly high risk of CS delivery.[15],[16]

During labor with no ROM, uterine contractile forces exert pressure on the fetal membranes, leading to a centrifugal force on the cervix and subsequent cervical dilatation. Intra-amniotic infection or inflammation may result from an increased duration of ROM in cases of early ROM and is responsible for a higher risk of CS because of inadequate uterine contractions resulting from uterine inflammation. A significantly higher CS rate was observed (10.7% vs. 2.7%) with late amniotomy (P = 0.049).[17] However, our study findings did not support this explanation, as we had already administered misoprostol to ripen the cervix before amniotomy. Women in the early amniotomy group reported a significantly shorter duration of labor by about 4 h than those in the late amniotomy group (12.60 ± 5.36 h vs. 16.67 ± 7.26 h).

This was consistent with the findings of a study conducted by Doulaveris et al., which reported a decrease in the duration of labor in women who underwent early amniotomy compared to that in those who underwent late amniotomy (860.1 ± 80.4 min [14.3 h] vs. 1,020.8 ± 50.8 min [17 h], P < 0.001).[17] In addition, Ghafarzadeh et al. found a reduction in the duration of labor in the early amniotomy group (7.5 ± 0.7 h) compared to that in the late amniotomy group (9.9 ± 1.0 h) (P < 0.001).[18] Other studies by Macones et al. and Brisson-Carroll et al. found that routine early amniotomy is associated with a reduction in the duration of labor, as early amniotomy shortens the amniotomy delivery interval by more than 2 h (19.0 vs. 21.3 h).[13],[19]

In addition, Garite et al. found that early amniotomy shortened the duration of labor (12 ± 0.55 min vs. 15 ± 0.34 min) and decreased the need for oxytocin augmentation (76 in the late amniotomy group vs. 36 in the early amniotomy group, P < 0.001), which is consistent with our study.[20] Additionally, in our study, fetal distress accounted for most of the indications for CS in both groups; however, while group A had a lower rate than group B, (7 [53.9%] and 12 [63.2%] respectively), the difference was not statistically significant (P > 0.05).

Consistent with our results, Zahran et al. found that the CS rate due to fetal distress was lower in the early than in the late amniotomy group (16 [10.0%] vs. 21 [13.3%]).[21] However, Brisson-Carroll et al. found an association between early amniotomy and CS for fetal distress (OR, 1.26; 95% CI, 0.96–1.66), suggesting that amniotomy should be reserved for women with abnormal labor progress, which was not consistent with our findings.[19] Our study also demonstrated less need for oxytocin in early amniotomy cases compared with that in late amniotomy cases (29 [48.3%] vs. 33 [55.0%], P = 0.464). This is in line with the findings of Fraser et al., who reported a trend toward less frequent use of oxytocin among women who underwent early amniotomy (36.0% vs. 41.0%), with a lower maximum oxytocin concentration (30.05 mU/min vs. 39.68 mU/min; P = 0.001), compared to that in women who underwent late amniotomy.[22]

Garite et al. found less need for oxytocin augmentation in the early elective amniotomy group (76 in the late amniotomy group vs. 36 in the early amniotomy group, P < 0.001), which was consistent with our results. Considering the suggested effect of amniotomy on the efficiency of uterine contractions, this finding should not be surprising and may have positive practical implications in resource-poor settings, which are prevalent in developing countries.[20] For instance, the decrease in intense pain caused by oxytocin use in the augmentation of labor can be reduced by early amniotomy in eligible women. Our results also indicated that early amniotomy was associated with fewer cases of meconium-stained liquor (10.0% vs. 15.0%), less frequent APGAR scores < 7 at 1 and 5 min (10% vs. 20% and 5.0% vs. 10.0%, respectively), and lower rates of NICU admissions (3.3% vs. 5.0%), which might be due to the associated shorter induction-to-delivery interval in the early than in the late amniotomy group, although this difference was not statistically significant between the groups.

These results are confirmed by several studies, such as Macones et al., Boulvain et al., and Doulaveris et al., who reported that routine early amniotomy was associated with a reduction in abnormal 5-min APGAR scores and the need for NICU admissions (6.6% vs. 8.6%) or APGAR scores <7 at 1 min (6.2% vs. 7.5%) for the early versus late amniotomy group.[13],[17],[23] In our study, no cases of umbilical cord prolapse were observed, despite the possible causal relationship with amniotomy.

This finding may provide further evidence for the safety of early amniotomy in uncomplicated labor.[24] Additionally, the rate of maternal fever between groups A and B decreased (13.3% and 18.3%, respectively) in the current study, although the difference was not significant. This result is consistent with the findings of Gagnon-Gervais et al.,[25] who showed a decrease in the incidence of intrapartum fever, but is not consistent with the findings of Macones et al., who showed a nonsignificant increase in maternal fever between the groups.[13]

The strengths of our study were as follows: (1) it was a randomized clinical trial, (2) all patients were nullipara and were randomly assigned to undergo either early or late amniotomy, and (3) two methods of induction were studied: amniotomy and vaginally delivered misoprostol.

In conclusion, the vaginal delivery of misoprostol followed by early amniotomy for IOL was associated with a shorter duration of labor and a decreased need for oxytocin augmentation. No significant difference was found between the early and late amniotomy groups regarding CS rate and maternal and neonatal complications. More studies are needed to confirm the advantages of early versus late amniotomy on IOL in nulliparous women after vaginal misoprostol, noted in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Smyth RM, Markham C, Dowswell T. Amniotomy for shortening spontaneous labour. Cochrane Database Syst Rev 2013;6:CD006167. doi: 10.1002/14651858.CD006167.pub4.  Back to cited text no. 9
    
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Kim SW, Nasioudis D, Levine LD. Role of early amniotomy with induced labor: A systematic review of literature and meta-analysis. Am J Obstet Gynecol 2019;1:100052. doi: 10.1016/j.ajogmf.2019.100052.  Back to cited text no. 11
    
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Lee SM, Park JW, Park CW, Yoon BH. "Early rupture of membranes" during induced labor as a risk factor for cesarean delivery in term nulliparas. PLoS One 2012;7:e39883. doi.: 10.1371/journal.pone. 0039883.  Back to cited text no. 14
    
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Garite TJ, Porto M, Carlson NJ, Rumney PJ, Reimbold PA. The influence of elective amniotomy on fetal heart rate patterns and the course of labor in term patients: A randomized study. Am J Obstet Gynecol 1993;168:1827-31. doi: 10.1016/0002-9378(93)90697-h.  Back to cited text no. 20
    
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