Labor induction is a critical obstetric intervention aimed at initiating uterine contractions to achieve vaginal delivery before the spontaneous onset of labor. It is often indicated when the benefits of early delivery outweigh the risks of continued pregnancy, including conditions such as post-term pregnancy, hypertensive disorders, premature rupture of membranes, and fetal growth restriction. Induction of labor (IOL) thus plays a vital role in contemporary obstetric practice to optimize maternal and fetal outcomes.[1]

Oxytocin and misoprostol are two of the most widely used pharmacological agents for labor induction. Oxytocin, a synthetic analogue of the naturally occurring hormone, acts primarily by stimulating uterine smooth muscle contractions. It has been the mainstay of labor induction for decades due to its efficacy and relatively predictable pharmacodynamics. Oxytocin is typically administered intravenously with careful dose titration, which allows for precise control of uterine activity.[2]

Misoprostol, a synthetic prostaglandin E1 analogue, is increasingly employed for cervical ripening and labor induction. It promotes cervical softening and dilation by remodeling the extracellular matrix and stimulates uterine contractions. Misoprostol offers several practical advantages: it can be administered via multiple routes (oral, vaginal, sublingual), has a relatively long shelf-life, is inexpensive, and does not require intravenous access, making it particularly useful in low-resource settings.[3][4]

Despite widespread use, controversies persist regarding the relative safety and efficacy of oxytocin versus misoprostol, especially in nulliparous women. Nulliparous women, having no prior vaginal deliveries, often present with an unfavorable cervix, which can complicate induction and increase the risk of prolonged labor or cesarean section. The success of induction in this group is thus a topic of considerable clinical importance.[5]

Aim

To compare the effectiveness of induction of labor with oxytocin versus misoprostol in nulliparous women.

Objectives

1. To compare the induction-to-delivery interval between oxytocin and misoprostol in nulliparous women.
2. To evaluate the rate of successful vaginal delivery within 24 hours in both groups.
3. To assess the maternal and fetal outcomes including complications related to each induction agent.

Source of Data: Data was collected from nulliparous pregnant women admitted for induction of labor at the Department of Obstetrics and Gynecology, [Hospital Name], a tertiary care center.

Study Design: This was a prospective comparative observational study.

Study Location: The study was conducted in the labor ward and antenatal wards.

Study Duration: The study duration was from January 2024 to December 2024, covering a period of 12 months.

Sample Size: A total of 200 nulliparous women requiring labor induction were enrolled and divided equally into two groups of 100 each.

Inclusion Criteria:

• Nulliparous women aged 18-35 years.
• Singleton pregnancy with cephalic presentation.
• Gestational age ≥37 weeks confirmed by reliable dating.
• Indications for induction of labor - post-term pregnancy, gestational hypertension.
• Bishop score ≤6 indicating an unfavorable cervix.

Exclusion Criteria:

• Previous uterine surgery or cesarean section.
• Multiple pregnancies.
• Malpresentation or fetal anomalies.
• Contraindications to vaginal delivery - placenta previa.
• Known hypersensitivity to prostaglandins or oxytocin.
• Signs of fetal distress prior to induction.

Procedure and Methodology: Eligible participants were randomly assigned to one of two groups:

• Group A (Oxytocin Group): Labor induction was initiated with intravenous oxytocin infusion starting at 2 mU/min, with incremental increases every 30 minutes based on uterine contraction pattern, aiming for 3-4 contractions every 10 minutes lasting 40-60 seconds, under continuous fetal monitoring.
• Group B (Misoprostol Group): Induction was initiated with vaginal misoprostol 25 mcg inserted into the posterior vaginal fornix every 4 hours, up to a maximum of 6 doses or until active labor was established.

All women were monitored continuously for uterine activity, fetal heart rate, and signs of complications such as uterine hyperstimulation or fetal distress. The progress of labor was assessed by routine vaginal examinations and the partogram.

Indications for cesarean section included failure to progress, non-reassuring fetal heart patterns, or other obstetric emergencies.

Sample Processing: Relevant maternal parameters such as pulse, blood pressure, uterine activity, and fetal heart rate were recorded periodically. Neonatal outcomes including Apgar scores at 1 and 5 minutes were documented. Data on duration from induction to delivery, mode of delivery, and any maternal or neonatal complications were collected and recorded on standardized proformas.

Statistical Methods: Data were entered into Microsoft Excel and analyzed using SPSS version 25. Quantitative variables (induction-delivery interval) were expressed as mean ± standard deviation and compared using Student’s t-test. Qualitative variables (mode of delivery, complications) were expressed as percentages and compared using Chi-square test or Fisher’s exact test as appropriate. A p-value of <0.05 was considered statistically significant.

Data Collection: Data was collected prospectively from patient records, direct observations during labor, and follow-up until discharge. Confidentiality of patient information was maintained throughout the study. Written informed consent was obtained from all participants before enrollment

Table 1: Baseline Demographic and Clinical Characteristics of Study Population (N=200)

Table 1 presents the baseline demographic and clinical characteristics of the study population comprising 200 nulliparous women undergoing induction of labor, divided equally into two groups receiving either oxytocin or misoprostol. The mean age in the oxytocin group was 27.83 ± 4.76 years compared to 28.14 ± 4.89 years in the misoprostol group, with no statistically significant difference between groups (t = 0.57, p = 0.57). Gestational age was comparable between groups, averaging 39.61 ± 1.12 weeks in the oxytocin group and 39.72 ± 1.06 weeks in the misoprostol group (t = 0.87, p = 0.38). The pre-induction Bishop scores, an indicator of cervical readiness, were similar, measuring 4.21 ± 1.32 and 4.08 ± 1.45 respectively (t = 0.62, p = 0.53). Indications for induction, including post-term pregnancy, gestational hypertension, oligohydramnios, and other causes, showed no significant differences in proportions between the two groups. Additionally, body mass index (BMI) averages were comparable (24.37 ± 3.89 vs. 24.85 ± 4.12; t = 1.02, p = 0.31), confirming homogeneity of baseline characteristics.

Table 2: Comparison of Induction-to-Delivery Interval between Oxytocin and Misoprostol Groups (N=200)

Table 2 compares the primary outcome measure of induction-to-delivery interval between the two groups. The mean induction-to-delivery time was significantly shorter in the misoprostol group (7.56 ± 2.98 hours) than in the oxytocin group (9.87 ± 3.42 hours), with a mean difference ranging from 1.61 to 3.33 hours (t = 5.89, p < 0.001). Similarly, the mean duration of active labor was reduced in the misoprostol group (4.13 ± 1.87 hours) compared to the oxytocin group (5.42 ± 2.11 hours), showing a statistically significant difference (t = 5.08, p < 0.001). These results indicate that misoprostol was associated with a more rapid progression of labor.         

Table 3: Rate of Successful Vaginal Delivery within 24 Hours (N=200)

Table 3 details the success rates of vaginal delivery within 24 hours. The misoprostol group had a significantly higher rate of vaginal deliveries within this timeframe (85.0%) compared to the oxytocin group (72.0%), with the difference in proportions statistically significant (χ² = 5.12, p = 0.024; 95% CI 0.03 to 0.23). Correspondingly, the cesarean section rate was lower in the misoprostol group (15.0%) than in the oxytocin group (28.0%), supporting the increased effectiveness of misoprostol in achieving timely vaginal delivery.

Table 4: Maternal and Fetal Outcomes Including Complications (N=200)

Table 4 summarizes maternal and fetal complications observed in both groups. Although uterine hyperstimulation occurred more frequently in the misoprostol group (18.0%) compared to the oxytocin group (11.0%), this difference was not statistically significant (χ² = 2.06, p = 0.15). Fetal distress was also higher in the misoprostol group (16.0% vs. 9.0%), but again without significant difference (χ² = 2.62, p = 0.11). Incidences of postpartum hemorrhage, low neonatal Apgar scores at 5 minutes, and neonatal intensive care unit admissions were comparable between groups, with no statistically significant differences observed (all p > 0.05). Overall, the safety profiles of both induction agents appeared similar in this study.

Baseline Demographic and Clinical Characteristics (Table 1): The baseline characteristics of the study groups were well matched, with no significant differences in age, gestational age, Bishop Score, BMI, or indications for induction. The mean maternal age was approximately 28 years in both groups, consistent with similar studies such as Sanchez-Ramos L et al. (2024)[6] and Acharya T et al. (2017)[4], which reported comparable maternal demographics in their cohorts. The parity status being nulliparous and gestational ages around 39-40 weeks align with typical term induction populations, ensuring homogeneity for valid comparison. The indications for induction, predominantly post-term pregnancy and gestational hypertension, mirror findings from Wang L et al. (2016)[7], confirming the representativeness of the study population.

Induction-to-Delivery Interval (Table 2): This study demonstrated a significantly shorter induction-to-delivery interval in the misoprostol group (7.56 ± 2.98 hours) compared to the oxytocin group (9.87 ± 3.42 hours), with a mean difference of 1.61 to 3.33 hours (p < 0.001). The duration of active labor was also significantly less with misoprostol. These results are in agreement with the meta-analysis by Taliento C et al. (2023)[8], who found that vaginal misoprostol reduced time to delivery more effectively than oxytocin in labor induction. Similarly, Ahmed RH et al. (2023)[9] observed shorter induction-to-delivery intervals with prostaglandin agents compared to oxytocin alone. The more rapid cervical ripening and uterotonic effects of misoprostol contribute to this accelerated labor progression.

Rate of Successful Vaginal Delivery within 24 Hours (Table 3): The higher vaginal delivery rate within 24 hours in the misoprostol group (85.0%) versus oxytocin (72.0%) was statistically significant (p = 0.024), indicating better induction efficacy with misoprostol. The cesarean rate was correspondingly lower in the misoprostol group (15.0% vs. 28.0%), which is consistent with findings by Adhikari EH et al. (2022)[10] and Pergialiotis V et al. (2023)[11], both reporting higher vaginal delivery rates and reduced cesarean sections with misoprostol induction compared to oxytocin. Vilas-Boas LS et al. (2024)[12] also reported a trend favoring misoprostol for vaginal delivery success within 24 hours, supporting the present findings.[2]

Maternal and Fetal Outcomes (Table 4): While uterine hyperstimulation and fetal distress occurred more frequently in the misoprostol group (18.0% and 16.0%, respectively) than in the oxytocin group (11.0% and 9.0%), these differences did not reach statistical significance. This is consistent with previous studies highlighting a higher but acceptable rate of hyperstimulation with misoprostol, as noted by Liu A et al. (2014)[13] and Wollmann CL et al. (2017)[14]. No significant differences were observed in postpartum hemorrhage, low Apgar scores, or NICU admissions, indicating comparable safety profiles. Similarly, Marsdal KE et al. (2018)[15] and Bender WR et al. (2024)[16] reported no significant increase in adverse maternal or neonatal outcomes with misoprostol versus oxytocin. The slightly higher incidence of hyperstimulation underscores the need for careful monitoring when using misoprostol.

This study demonstrated that misoprostol is more effective than oxytocin in inducing labor in nulliparous women, as evidenced by significantly shorter induction-to-delivery intervals and higher rates of vaginal delivery within 24 hours. Although the incidence of uterine hyperstimulation and fetal distress was higher with misoprostol, these differences were not statistically significant, and maternal and neonatal outcomes were comparable between groups. Misoprostol offers a practical and efficacious alternative to oxytocin, particularly in settings where rapid labor induction is desired. Careful monitoring is essential to mitigate potential complications related to uterine hyperactivity.

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