Pre-induction cervical ripening and hygroscopic cervical dilators in pre-labor induction

Abstract

Introduction

Induction of labor (IOL) is becoming a universal topic in Obstetrics, when the risk of continuing a pregnancy outweighs the benefits. Preinduction is a more recent tool to prepare the cervix when the BISHOP-score is low. About one-third of IOL cases require cervical ripening, which is the physical softening, thinning, and dilation of the cervix in preparation for labor and birth. We report a single center experience regarding the use of hygroscopic dilators in the pre-labor phase to obtain cervical ripening before labor induction.

Materials & Methods

We conducted a retrospective observational study comparing patient records from the Gynecology and Obstetrics Unit in “Santo Stefano” Hospital in Prato, Tuscany. The inclusion criteria for participants were women who had undergone pre-labor induction because of a BISHOP-score < 3. The gestational age of all the pregnant women was at term (> 37 weeks).

Results

From January 2022 to April 2022, a total of 581 women delivered at term of gestational age at the Gynecology and Obstetrics Unit in “Santo Stefano” Hospital. Cervical ripening was necessary for 82 women with a Bishop score < 3 and hygroscopic cervical dilators were used in 35/82 (42.7%) patients. All patients showed a change in Bishop-score upon removal of the dilators. All 35 patients (100%) reported an increase in terms of consistency and dilation of the cervix but not in terms of length. None of the patients reported discomfort during the 24 h that they kept the hygroscopic dilators in place. No patients reported uterine tachysystole on cardiotocographic tracing, vaginal bleeding, rupture of membranes or cervical tears.

Conclusions

Our results are in line with those in the literature, demonstrating the validity of hygroscopic dilators in cervical maturation of pregnancies at term and their efficacy was again highlighted in terms of both maternal and fetal safety and patient satisfaction.

Keywords:

• Induction of labour
• cervical ripening
• cervical maturation
• hygroscopic dilators
• Bishop score

Introduction

Induction of labor (IOL) is becoming a universal topic in Obstetrics, when the risk of continuing a pregnancy outweighs the benefits [1]. Over the past decades, the use of labor induction has increased. In the United States, approximately 1 out of 4 women undergo this procedure [2]and in Italy 31.5% of births in the year 2021 underwent IOL [2].

Preinduction is a more recent tool to prepare the cervix when BISHOP-score is low [3]. About one-third of IOL cases require cervical ripening, which is the physical softening, thinning, and dilation of the cervix in preparation for labor and birth [4].

Cervical ripening can be obtained by pharmacological methods, such as administration of vaginal or oral prostaglandins, or by mechanical methods, such as hygroscopic dilators or a cervical balloon. The usefulness and safety of mechanical means has been demonstrated over the years and their reduced risk of uterine hyperstimulation [5].

Although the data about preinduction of labor are not consistent, to date we know that synthetic osmotic dilators are non-inferior to the Foley balloon in terms of safety and efficacy [5].

We report a single-center experience regarding the use of hygroscopic dilators in the pre-labor phase to obtain cervical ripening before labor induction.

Methods

We conducted a retrospective observational study describing patient records from the Gynecology and Obstetrics Unit in “Santo Stefano” Hospital in Prato, Tuscany.

The inclusion criteria for participants were women who had undergone pre-labor induction because of a BISHOP-score < 3. The gestational age of all the pregnant women was at term (> 37 weeks). The course of pregnancy was physiological until the end of gestation, after which, due to a clinical event (e.g. pressure rise, reduction of amniotic fluid) it was decided to intervene by initiating cervical maturation.

The study covers all non-selected cases in the period from January to April 2022 as before this date the only mechanical means used was represented by the CRB.

The hygroscopic cervical dilators were placed by trained medical personnel. Before the device placement, patients underwent continuous cardiotocography monitoring for 20 min.

Up to 5 synthetic osmotic dilator rods (Dilapan-S ®) were inserted into the cervical canal under direct visualization. The devices were left in the cervix for at least 12 h and no longer than 24 h. After placement, patients were monitored with continuous cardiotocography for at least 30 min. All the patients remained in the hospital, and were allowed to walk, have a shower, and perform regular activities during that period. The patients were instructed to report bleeding, pain, or any symptoms. All symptoms were registered in the medical record.

The primary outcome was the efficacy of hygroscopic dilators for cervical ripening during term-labor induction, which was assessed in terms of variation of the BISHOP score.

Secondary outcomes were the safety of mother and fetus and the absence of women’s discomfort to propose outpatient pre-induction in low Bishop score pregnancies.

Statistical analysis

Descriptive statistics were used to summarize the data. We reported and assessed our experience regarding the use of hygroscopic dilators in the pre-labor phase to obtain cervical ripening before labor induction. All analyses were performed using Microsoft Excel.

Results

From January 2022 to April 2022, a total of 581 women delivered at term of gestational age at the Gynecology and Obstetrics Unit in “Santo Stefano” Hospital.

Among these patients, 186/581 (32%) underwent induction of labor: 82/186 (44.1%) showed an unripened cervix (Bishop score <3).

Among the patients with an unripened cervix, cervical ripening using hygroscopic cervical dilators was used in 35/82 (42.7%) patients (Figure 1).

Figure 1. Flow diagram of eligible patients.

Indications for induction of labor were: 9/35 (26%) gestational diabetes, 7/35 (20%) blood pressure elevation, 6/35 oligoamnios (17%), 6/35 colestasis (17%), 5/35 (14%) protracted pregnancy, 1/35 (3%) hypothyroidism, and 1/35 (3%) thrombophilia.

Characteristics of the patients who received hygroscopic dilators are summarized in Table 1. None of the patients had previous cesarean sections or severe obesity.

Table 1. Characteristics of patients.

Characteristics of hygroscopic-dilators patients	N°	Range
Age, years (median)	31	22–44
BMI^a, kg/m^2 (median)	24	18–33
Parity
Nulliparous	12 (34.4%)
Multiparous	23 (65.7%)
Gestational age
37 weeks	7 (20,0%)
38 weeks	5 (14.3%)
39 weeks	9 (25,7%)
40 weeks	9 (25,7%)
41 weeks	5 (14.3%)
Patients with previous cesarean section	0
N° of inserted dilators, median	5	3–5
Change in Bishop score	35 (100 %)
Bishop-score before dilapan, median	2	0–3
Bishop-score after dilapan, median	4	2–6
Patients with other rounds of induction	27 (79.4 %)
Induction to delivery, days	2	1–4

^a BMI: body mass index.

The median number of dilators inserted in the cervix was from 3 to 5 and they were left in place from 12 to 24 h. All the patients showed a change in Bishop-score upon removal of the dilators. Specifically, the Bishop score changed from an initial median value of 2 (range 0–3) to a post-induction value of 4 (range 2–6). All 35 patients (100%) reported an increase in terms of consistency and dilation of the cervix but not in terms of length.

Table 2 summarizes the clinical and safety outcomes.

Table 2. Clinical, safety and neonatal outcomes.

CLINICAL AND SAFETY OUTCOMES
		N°	%
Number of cesarean deliveries		4	11.4 %
Indications for cesarean delivery	Nonreassuring fetal heart rate	1	25.0 %
	Fever during labor	1	25.0 %
	Failed obstetric vacuum cup	2	50.0 %
Safety outcomes	Uterine tachysystole^a	0	.0 %
	Vaginal bleeding^a	0	.0 %
	Rupture of membranes^a	0	.0 %
	Cervical lacerations^a	0	.0 %
Discomfort		0	–
Neonatal outcomes	pH median (range)	7.25 (7.02–7.45)	–
	Apgar, median (range)	10 (9-10)	–

^a During cervical ripening interval.

Moreover, there were no cases of the rupture of membranes either during dilator placement or within 12 to 24 h after placement. None of the patients reported discomfort during the 24 h that they kept the hygroscopic dilators in place.

Eight patients (20.6%) started labor spontaneously after the cervical dilator, while the number of patients who required other induction methods (oral or vaginal prostaglandins) was 27/35 (79.4%) and the median time from induction to delivery was 2 days (range 1–4).

All newborns were alive and neonate characteristics are specified in Table 2.

Regarding safety outcomes, no patients reported uterine tachysystole on cardiotocographic tracing, vaginal bleeding, rupture of membranes or cervical tears.

Regarding the outcome of way of delivery for all our patients, 4/35 (11.4%) patients had a cesarean-section during labor: 1 because of non-reassuring heartbeat, 1 for hyperpyrexia and 2 for failed obstetric vacuum cup application.

Discussion

As revealed by recent evidence, patients treated with an igroscopic cervical dilator report better satisfaction [6], and the cervical dilator does not have any parts that protrude from the vagina, making it the ideal candidate for outpatient cervical ripening to reduce hospitalization time and inpatient costs.

There have been several studies in outpatient cervical ripening [7–15] but only in 2022 the group of Saad et al. compared the use of hygroscopic dilators in inpatient and outpatient women showing how outpatient cervical ripening with a cervical osmotic dilator decreased hospital stay compared with inpatient ripening, without significant adverse outcomes [16].

Following the results of the ARRIVE Trial [1], a randomized trial that compared expectant labor versus induction of labor, induction of labor at 39 weeks in low-risk nulliparous women did not result in a significantly lower frequency of a composite adverse perinatal outcome, but it resulted in a significantly lower frequency of cesarean delivery. Furthermore, the choice of a safe, practical, and cost-effective induction method (will be) is a priority.

Nowadays, the characteristics of pregnant women have changed, thanks to the increase in our clinical knowledge, in-vitro fertilization, and advances in medicine and this leads us to resort increasingly to labor inductions.

At the same time, it must be remembered that the use of mechanical means is not without medico-legal pitfalls since the induction of labor by mechanical methods (amniotomy or Foley’s catheter) is associated with an increased risk of rupture of the previous uterine scar but lower than induction with prostaglandins. Regarding the communication with women with a previous cesarean birth in relation to induction or augmentation of labor, the Royal College of Obstetricians & Gynecologists’ guidelines declare that women should be informed of the two- to three-fold increased risk of uterine rupture and around 1.5-fold increased risk of cesarean delivery in induced and/or augmented labor compared with spontaneous VBAC labor. A senior obstetrician should discuss the following with the woman: the decision to induce labor, the proposed method of induction, the decision to augment labor with oxytocin, the time intervals for serial vaginal examination and the selected parameters of progress that would necessitate discontinuing VBAC [17].

For this reason, the trial of Labor after Cesarean (TOLAC) is an option that should also be offered in cases with an indication for induction of labor.

Regarding cervical ripening, there has been increasing interest in recent years about which mechanical method is the most effective.

In 2019, Saad et al. published a randomized trial, DILAFOL trial [6] comparing hygroscopic cervical dilators and Foley balloons in 419 patients with an unfavorable cervix (≤3 cm dilated and ≤60% effaced) at term (≥ 37 week of gestation). The results showed that vaginal delivery was more frequently associated with hygroscopic dilators than with the Foley (81.3% vs 76.1%), although the difference was not so striking as to justify a superiority of this device. Concerning neonatal and maternal adverse events, no significant difference was found, while interestingly, patients with the hygroscopic dilators were much more satisfied than those with the Foley when performing daily activities, relaxing, and sleeping, showing a significant difference between the two methods.

Given the efficacy of dilators in terms of maternal and fetal safety, cervical ripening through an outpatient strategy is also being considered, allowing more time for cervical ripening and less time in the labor and delivery room.

In 2022, a study by A.F Saad et al. [16] whose objective was to evaluate whether outpatient cervical ripening with a synthetic osmotic dilator reduces the length of hospital stay in term pregnancies undergoing labor induction. The results showed that the proportion of participants with hospital stays longer than 48 h was lower in the outpatient group compared with the inpatient group (89 [53%] vs 152 [89%], relative risk [RR] .60, 95% CI .52–.70). Women in the outpatient group had a shorter total length of stay and time from admission to active labor. They were more likely to have a vaginal delivery within 24 h of admission and were less likely to receive analgesics during ripening. Route of delivery and other maternal and neonatal outcomes were not significantly different between groups.

The validation of such an outpatient strategy would allow a profitable reduction of hospital costs and, with the ongoing COVID-19 pandemic, the reduction of hospital burdens would certainly be a great incentive and would allow patients to reduce their hospital stay, avoiding dangerous exposures.

This cost analysis was investigated by S.J. Saunders et al. [18], as they demonstrated that cervical ripening with cervical dilators in patients at term of gestation resulted in hospital savings of US$ 689 per delivery, with women spending 1.48h less time in the labor and delivery room and .91h less in the postpartum recovery unit. Also, the cesarean-section rate decreased by 3.78 percentage points (23.28% decreased to 19.50%).

Our study however has some limitations. First of all, the small number of patients included in our analysis represents a little sample size from which it is possible to draw conclusions but at the same time it allows us to underline the effectiveness of cervical dilators, as has already been stated in the literature. Secondly, the absence of data on neonatal outcomes is also an important limitation but our study was aimed at cervical maturation and approximately 80% of patients underwent other induction methods subsequent to dilators so the results would not be exclusive to this method.

At the same time, our work, even if restricted in scale, represents one of the few works in the literature regarding the use of hygroscopic dilators in cervixes with an unfavorable Bishop and the data on maternal-fetal safety certainly suggests implementing this means on larger populations and also in outpatient settings.

Our results are in line with those in the literature, demonstrating the validity of hygroscopic dilators in cervical maturation of low-risk pregnancies at term, and their efficacy was again highlighted in terms of both maternal and fetal safety and patient satisfaction.

On this basis, it would incentivize an outpatient strategy for cervical maturation. While still respecting maternal-fetal safety parameters, the implementation of this strategy would reduce the time that women spend in the hospital for delivery and reduce the rate of cesarean sections, which is one of the main goals of obstetrics. At the same time, reducing hospital stays would result in significant savings in hospital costs.

In conclusion, our study represents the first step in our experience to validate the safety of using mechanical cervical methods to project an outpatient pre-labor induction.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

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Funding

The author(s) reported there is no funding associated with the work featured in this article.