Introduction

The rate of labor induction has increased over the past decade, and may continue to increase following recent studies concluding that elective induction of labor in low-risk nulliparous individuals is not associated with increased risk of cesarean delivery and therefore may be a reasonable approach in select populations. ^, Taken in a broader context, labor induction lasts longer than spontaneous labor, raising concerns about intrapartum and postpartum complications, including intraamniotic infection (IAI), prolonged exposure to oxytocin, and hemorrhage. Inductions may also negatively affect hospital resource utilization and patient throughput, potentially leading to increased medical costs.

Previous literature has evaluated the relationship between intravenous fluid and the duration of spontaneous labor, both in terms of fluid rate and dextrose content. A 2013 Cochrane review including 9 trials and 1781 individuals reported that increased intravenous fluid at 250 cc/h was associated with shorter labor duration among spontaneously laboring individuals when compared with various standard hydration protocols (125 cc/h, ad libitum oral hydration, or combination of the 2). A 2017 meta-analysis of 7 randomized trials compared 125 cc/h with 250 cc/h in 1215 spontaneously laboring nulliparas. In this meta-analysis, a higher intravenous fluid rate was associated with a lower rate of cesarean delivery and shorter duration of labor. A 2018 meta-analysis demonstrated that the addition of dextrose to intravenous fluid is associated with a shorter first stage of labor.

The theoretical basis for this finding is rooted in the idea that adequate hydration and dextrose optimize muscle function. As such, adequate hydration of the myometrium is hypothesized to improve uterine contractility, leading to shorter duration of labor and increased success of vaginal delivery. Although this relationship has been evaluated in subjects presenting in spontaneous labor, its effect on labor induction has not been studied. The purpose of this study was therefore to investigate whether increased intravenous fluid is associated with a shorter duration of labor in nulliparous individuals undergoing labor induction.

Materials and Methods

This study was a double-blinded, randomized controlled trial conducted between 2016 and 2020 at an academically-affiliated community hospital. Eligible participants were nulliparous individuals with a singleton vertex fetus presenting for induction of labor with a Bishop score of ≤6. Exclusion criteria included a gestational age <36 weeks, evidence of hypertension at time of enrollment, nonreassuring fetal heart rate tracing precluding induction, suspected IAI at time of enrollment, presence of uterine scars, obesity with a body mass index (BMI) ≥50, intrauterine growth restriction, or known maternal cardiac disease. Following a cervical exam to confirm the Bishop score, subjects were approached for informed consent and then randomized to 1 of 2 groups via a 1:1 computer-generated envelope system. Group 1 received 125 cc/h of normal saline and group 2 received 250 cc/h of normal saline. Study fluids were initiated at the time of study consent and were discontinued at the time of delivery. For both groups, the participants and care providers were blinded to the fluid rate by placing an index card over the display on the intravenous pump. Study participants were otherwise permitted oral fluid intake per standard labor protocol, generally including sips of water and ice chips. The induction agent, oxytocin use, amniotomy, and all other aspects of labor management were at the discretion of individual providers.

Participant demographics, the Bishop score at time of enrollment, and indication for induction were collected for all participants. The primary outcome measure was length of labor, which was defined as the time from initiation of study fluids to delivery, consistent with previous trials. Secondary outcome measures included the duration of labor and rate of delivery within 24 hours among those that delivered vaginally, and length of each stage of labor. The first stage of labor was defined from initiation of study fluids until complete cervical dilation, and the second stage was defined from complete dilation to delivery. Additional secondary outcomes included mode of delivery, neonatal outcomes, and presence of IAI. Neonatal outcomes included birthweight, Apgar scores, need for phototherapy for neonatal jaundice, and need for admission to the neonatal intensive care unit (NICU). The presence of IAI was determined on the basis of either clinical criteria (physician documentation of suspected IAI and/or initiation of standardly used antibiotic therapy), placental evidence of infection on pathology, or both.

Sample size was determined using a power calculation based on previously reported literature regarding induction of labor in nulliparous individuals. Duration of labor induction among nulliparous individuals has been reported to range from 21 to 30 hours. To obtain 80% power to detect a 20% decrease in the duration of labor at a statistical significance level of 0.05, 73 participants were needed in each group. The sample size was increased to 90 per group for a total of 180 participants to account for participant withdrawal and enrollment errors.

Baseline characteristics, labor outcomes, and neonatal outcomes were described by percentage of patients for categorical variables and mean (standard deviation) for continuous variables. Group differences were assessed for significance using the chi-square test and independent t test, respectively. The primary outcome of labor duration was examined via intention-to-treat analysis, using a Cox regression analysis to account for potential influence of clinically relevant covariates, with the exception of maternal diabetes mellitus because of limited subjects in the 250-cc/h group with this condition. The mean duration of labor in each group was also described and compared using an independent sample t test. The bivariate examination of factors in relation to the intervention group was conducted using IBM SPSS Statistics, Version 25.0 (IBM Corp, Armonk, NY), whereas Cox regression analyses and median survival times with 95% confidence intervals (CIs) were obtained using RStudio, Version 1.2.5001 (RStudio, PBC, Boston, MA).

The trial received approval from the institutional review board and was registered at ClinicalTrials.gov ( ClinicalTrials.gov identifier: NCT02989571 ). The trial was funded through the Memorial Foundation.

Results

A total of 180 participants were enrolled. Seven individuals were removed from the study following randomization, and therefore the intention-to-treat analyses included 173 participants (89 receiving 125 cc/h and 84 receiving 250 cc/h). Of these individuals, additional 7 did not complete the study protocol ( Figure ). Reasons for the discontinuation of the study protocol included the development of preeclampsia (n=4) or the managing obstetrical provider’s decision to change the intravenous fluid (n=3).

Study screening and enrollment

Duffy et al. Increased intravenous fluid and nulliparous induction of labor. Am J Obstet Gynecol 2022 .

The baseline demographic characteristics are demonstrated in Table 1 . There were no group differences in maternal age, race, gestational age, Bishop score, or BMI on admission. There was a higher rate of maternal diabetes mellitus in the group receiving 125 cc/h (15.7% vs 3.6% in the group receiving 250 cc/h; P =.007). Of these cases, 77% had gestational diabetes mellitus and the remaining cases had type 2 diabetes mellitus. The median fetal birthweight among diabetic patients was 3500 g and the median Bishop score was 4.

The reasons for induction of labor and the initial methods of labor induction were similar between the groups ( Table 2 ). Table 3 describes the group differences in labor duration. The average length of labor was 27.8 hours for the group receiving 125 cc/h and 27.6 hours for the group receiving 250 cc/h ( P =.91). In a subanalysis in which the diabetic patients were removed from the analysis, the mean duration of labor did not significantly change (27.0 hours vs 27.4 hours). In the survival analyses, there was no difference in duration of labor, regardless of mode of delivery (hazard ratio [HR], 1.026; 95% CI, 0.759–1.388; P =.87) or whether only vaginal deliveries were considered (HR, 0.597; 95% CI, 0.616–1.322; P =.90). There was no influence on the associations between group and time to delivery related to BMI ( P =.86), Bishop score ( P =.53), race ( P =.92), or age ( P =.79).

Table 2

Labor characteristics in each group

Characteristic	125 cc/h N=89	250 cc/h N=84	P value a
Reason for induction			.72
Late-term gestation	44.9	44.0
Elective	15.7	21.4
Oligohydramnios	12.4	9.5
Advanced maternal age	3.4	6.0
Rupture of membranes	4.5	6.0
Other b	20.2	13.1
Initial method of induction			.54
Misoprostol	22.5	16.7
Foley	44.9	56.0
Pitocin	10.1	8.3
Foley and Pitocin	22.5	19.0
Use of oxytocin	89.9	92.9	.49
Use of epidural	87.6	88.1	.93
Duration of oxytocin, h	23.2 (10.7)	24.4 (13.7)	.65
Duration of membrane rupture, h	12.8 (8.7)	14.2 (9.5)	.35
Total intravenous fluid, mL	3476.8 (1674.1)	6984.5 (3186.8)	<.001

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. More than treatment refusal: a National Cancer Database analysis of adjuvant treatment refusal and racial survival disparities among women with endometrial cancer
2. Differences and similarities in endothelial and angiogenic profiles of preeclampsia and COVID-19 in pregnancy
3. Predictors of same-day discharge following benign minimally invasive hysterectomy
4. Mechanism of neonatal hypoglycemia after late preterm steroids: are fetal metabolic effects responsible?

Stay updated, free articles. Join our Telegram channel

Join