Induction of labor (IOL) is a routine obstetric procedure done to cause uterine contractions artificially prior to the onset of spontaneous labor. Labor induction occurs at a rate of about 22.5%, with prolonged pregnancy being the most common indication for induction (Martin et al.). IOL, in comparison to expectant management, has been linked with a decrease in perinatal mortality and is therefore a critical procedure in contemporary obstetrics (Bastani et al., 2011) [1].

IOL success is largely cervical readiness dependent, which has been classically evaluated by the Bishop score. The Bishop score assesses cervical dilation, effacement, consistency, position, and station of the fetal head to estimate the probability of successful vaginal delivery (Tan et al., 2007) [2]. But numerous studies have also pointed out the limitations of the Bishop score, citing its subjectivity and relatively low predictive value, particularly in women who have an unfavorable cervix (Mohamed et al., 2000) [3].

More recently, transvaginal ultrasonographic (TVUS) measurement of cervical length has become increasingly highlighted as a potential alternative or adjunct to the Bishop score for assessing cervical ripeness. Theoretically, TVUS is a more objective and reproducible assessment of the cervix than digital examination, which circumvents the limitation of digital assessment. Specifically, the supravaginal cervix, making up about 50% of the entire cervical length, is hard to estimate digitally. Also, cervical effacement, starting from the internal os, is not easily identified by digital assessment in the situation of a closed cervix (Ware & Raynor, 2000) [6].

A number of studies have shown the predictive ability of TVUS-measured cervical length for successful IOL and vaginal delivery. For example, Bastani et al. (2011) [1] reported that the area under the receiver-operating characteristic (ROC) curve for cervical length (0.69) was significantly better than that of the Bishop score (0.39) in predicting cesarean section after labor induction. Likewise, Tan et al. (2007) [2] indicated that TVUS was tolerated more by patients and had higher sensitivity for the prediction of cesarean delivery than the Bishop score. Additionally, Mohamed et al. (2000) [3] showed that women with cervical lengths <3.0 cm were likely to have shorter labor and successful vaginal delivery.

Further studies by Rane et al. (2003) [7] and Jo et al. (2012) [4] have supported the significance of cervical length measurement as a predictor of labor onset and induction-to-delivery intervals. Rane et al. (2003) [7] found that cervical length and parity were independent predictors of delivery via the vagina within 24 hours of induction. Also, Jo et al. (2012) [4] revealed that cervical length had a significant relation with spontaneous labor within seven days and post-term pregnancy outcomes among vaginal birth after cesarean (VBAC) candidates.

With these results, the incorporation of TVUS cervical length measurement into regular obstetric practice may increase the precision of labor induction prediction and enhance maternal and neonatal outcomes. This research seeks to assess the effect of cervical length, Bishop score, and maternal factors on labor induction success, further establishing the clinical value of TVUS as a valid instrument in obstetric decision-making.

Study Design and Setting

The study was a prospective observational study done at ESIPGIMSR, KK Nagar, Chennai, between January 2012 and November 2013. The aim of the study was to determine the predictive value of transvaginal cervical length, Bishop Score, and maternal characteristics for the success of labor induction.

Sample Size and Selection Criteria

250 pregnant women with singleton pregnancies between 37 and 42 weeks of gestation who were to be induced with PGE₂ gel were enrolled in the study. The sample size was computed using a 95% confidence interval and precision of 5%, calculated according to the formula:

Z2×(P(1−P)/d2)

Women participating in the study were pregnant with cephalic presentation, having a reactive cardiotocography (CTG), and a Bishop Score of below 4. Participating women who had Rh-negative pregnancies, pre-eclampsia, gestational diabetes mellitus, and post-dated pregnancy were also part of the study population. All patients received informed consent prior to the procedures of transvaginal ultrasound and induction of labor.

Women with antepartum hemorrhage, history of uterine operation, cephalopelvic disproportion, cardiopathy complicating pregnancy, asthma bronchialis, glaucoma, disease of the liver or kidney, hypersensitivity for prostaglandins, and women who underwent spontaneous onset of labor were all excluded from research.

Study Procedure

All the women fulfilling the criteria for inclusion were subjected to a digital examination in order to assess the Bishop Score, which was noted on a scale of 12. Women who had a Bishop Score of less than 4 were subjected to induction with intracervical PGE₂ gel. Transvaginal sonographic assessment of cervical length was conducted prior to induction with a LOGIQC Series machine using a 6-MHz transvaginal probe.

Transvaginal Cervical Length Measurement

The cervical length was taken with the patient in lithotomy position to have an empty bladder for better visualization. The transvaginal probe was inserted into the anterior fornix of the cervix, and the sagittal plane was adjusted to get a good view of the cervical canal from the internal to the external os in a straight line. The measurements were taken thrice consecutively, and the minimum value thus obtained was analyzed. Besides cervical length, the cervical canal diameter at the internal os level and the funnelling or wedging were also recorded.

Induction Protocol and Labor Monitoring

Labor induction was done with intracervical administration of 0.5 mg PGE₂ gel under aseptic conditions. Fetal heart rate was also monitored prior to and after administration of PGE₂. The patient was positioned laterally for 30 minutes after administration. In case the patient did not go into active labor, the dose was repeated after an interval of 8 hours, with a limit of three doses. Prior to each repeat dose, cervical length was re-measured by transvaginal ultrasound. Further doses were withheld if the patient had regular uterine contractions (three contractions in 10 minutes) or went into active labor.

Criteria for Successful Induction and Labor Progression

Active labor was established as cervical dilatation of 4 cm with 80% effacement, when artificial rupture of membranes was done. Successful induction was established as the onset of active labor within 72 hours of starting induction. Failure of induction was noted when the patient did not enter the active phase within 72 hours. Non-progress was indicated by a lack of cervical dilatation for 2 hours in the active phase or lack of fetal descent for 1 hour despite adequate uterine contractions. Failed induction of labor unrest was treated with cesarean section.

Outcome Measures

The main finding of the research was to identify the transvaginal cervical length that is associated with successful vaginal delivery within 72 hours of induction. Other secondary outcomes were the latent phase duration and the overall labor duration.

A total of 250 pregnant women with gestational ages ranging from 37 to 42 weeks who were induced with PGE₂ gel were studied. The research tested the impact of transvaginal cervical length (TVCL), Bishop Score, maternal factors, and induction parameters on delivery.

Maternal Demographics and Obstetric Profile

The average maternal age of the study group was 25.9 years (±3.5 SD), with 43.6% of them being in the 26–30 years age group. The primigravida women were 65.9%, and the multiparous women were 34.1%. Parity had a marked effect on the mode of delivery, with 73.3% of multiparous women having successful vaginal deliveries compared to only 43.2% of primigravida women. The incidence of lower-segment cesarean section (LSCS) was significantly more among primigravidas (56.7%) than among multiparas (26.7%), suggesting that parity was a determinant factor for induction outcomes (Table 1).

Furthermore, maternal BMI was also significantly related to delivery mode. The average BMI was 25.0 (±3.8 SD), and women with a BMI >25 had an increased rate of LSCS (63.6%) in comparison with women with a BMI of 20.1-25 (34.3%). This correlation was statistically significant (p < 0.0001), indicating that increased BMI could be one of the contributing factors to failed induction and prolonged labor (Table 2).

Cervical Length, Bishop Score, and Induction Outcomes

Mean TVCL prior to induction was 2.71 cm (±0.38 SD), with 53.6% of women having a TVCL <2.65 cm. Receiver Operating Characteristic (ROC) curve analysis picked a TVCL cutoff of 2.65 cm as an excellent predictor of delivery mode, with 97.8% specificity for vaginal delivery when TVCL was <2.65 cm and 97.4% specificity for LSCS when TVCL was ≥2.65 cm (AUC = 0.975; p < 0.0001). The average Bishop Score at induction was 2.74 (±1.2 SD), reflecting an initially unfavorable cervix. The median amniotic fluid index (AFI) was 8.41 cm, and there were prolonged latent phases in the LSCS cases, averaging 25.2 hours vs. 13.1 hours in vaginal delivery (p < 0.0001) (Table 3).

Induction Characteristics and Delivery Outcomes

Among the women studied, 70.8% delivered within 24 hours of induction with a mean induction-to-delivery interval of 20.1 hours. Only one dose of PGE₂ gel was enough for 47% of the women, and 22% needed three doses before entering active labor. The overall rate of vaginal delivery was 53.6%, whereas LSCS was done in 46.4% of the cases mainly for fetal distress (50%). Other reasons for LSCS were failure to progress in labor (30%) and non-reassuring fetal heart rate patterns (20%). These results point to the predictive role of TVCL and parity in the success of labor induction.

Neonatal and Maternal Outcomes

Neonatal courses were generally uneventful, with a mean birth weight of 2.69 kg (±0.37 SD) and 81.6% of infants presenting with an Apgar of 8/10. Complications like meconium-stained amniotic fluid were seen in 10.4% of patients, and 22% of neonates were admitted to NICU. Nonetheless, 72.8% of infants were free of complications. Maternal complications were rare, with postpartum hemorrhage seen in 4.4% of patients, which reflects a fairly safe induction procedure.

These results underscore the value of cervical length and parity as predictive factors of vaginal delivery success and can help tailor labor induction algorithms in clinical care.

Tables

Table 1: Parity and Mode of Delivery

Table 2: BMI and Mode of Delivery

Table 3: Cervical Length and Delivery Outcome

These results reinforce the clinical significance of cervical length, parity, and BMI in predicting the success of labor induction, aiding in informed decision-making for better maternal and neonatal outcomes.

The results of this study demonstrate the important predictive value of transvaginal cervical length (TVCL), Bishop Score, and maternal variables for the outcome of labor induction. The population mean TVCL was 2.71 cm, and the cutoff of 2.65 cm was noted to have strong predictive value for vaginal delivery. Women with a cervical length <2.65 cm had a 97.8% chance of successful vaginal delivery, whereas those with a TVCL ≥2.65 cm had a 97.4% chance of needing a cesarean section. These results concur with the findings of previous studies, most notably that of Fruscalzo et al. (2012) [10], who proved that cervix quantitative elastography and ultrasound-assessed cervical length were better predictors of the success of labor induction than the Bishop score. Similarly, Despain (2007) [11] stressed that cervical ultrasound evaluation, specifically TVCL measurement, exceeds the Bishop score in the prediction of successful induction,

validating the use of ultrasound in contemporary obstetric practice.

Parity was also an important factor affecting the outcomes of labor induction. Multiparous women in this research had a very much higher vaginal delivery rate (73.3%) than primigravida women (43.2%), with the latter having a greater cesarean delivery rate (56.7%). These findings are consistent with earlier reports demonstrating that multiparous women react more favorably to ripening agents in the cervix and are also more likely to deliver vaginally following induction. Almström et al. (1991) [13] investigated the application of PGE₂ gel for cervical ripening in women with intrauterine growth restriction and determined that the response to induction was better in multiparous women, with greater chances of having spontaneous vaginal delivery than in nulliparous women.

Maternal BMI also had a significant influence on the mode of delivery, with higher BMI having higher cesarean rates. Women with a BMI >25 had an LSCS rate of 63.6% versus 34.3% in those with a BMI of 20.1–25. This finding highlights the importance of maternal anthropometry in the outcome of labor and is consistent with the current literature that implies that obesity leads to prolonged labor and higher cesarean delivery rates because of dysfunctional uterine contractility and increased fetal macrosomia rates.

The application of PGE₂ gel in this research led to a successful vaginal delivery rate of 53.6%, with 70.8% of the subjects delivering within 24 hours. These results are consistent with previous research examining the effectiveness of intracervical prostaglandin administration. Ulmsten et al. (1982) [12] showed that PGE₂ gel was effective in inducing cervical ripening and labor, resulting in a high percentage of successful vaginal deliveries. Similarly, Silva-Cruz et al. (1985) [14] concluded that PGE₂ gel was useful in facilitating cervical preparedness for labor induction in patients with an unfavorable cervix, an observation in concordance with the present study's results indicating that cervical length and Bishop score at induction were factors affecting outcomes.

Neonatal outcomes within this study were positive, with a mean birth weight of 2.69 kg and Apgar score of 8/10 in 81.6% of infants. While 22% of neonates needed admission to the NICU, no complications were reported in most of them (72.8%). This is comparable to the outcomes reported by Norchi et al. (1992) [15], which assessed the outcome of multiple dosing of intracervical PGE₂ gel and similar neonatal status with a few cases of perinatal complication. In addition, Sahlin et al. (2007) [9] investigated the occurrence of glutaredoxin expression in the cervix at term pregnancy and early postpartum, especially with PG-induced births, emphasizing cervical tissue biochemical alteration that leads to labor following application of PGE₂. All these findings promote the safety and effectiveness of induction methods using prostaglandins in the conduct of successful labor.

In total, this study affirms TVCL, parity, and BMI as significant determinants of success in labor induction. The results concur with earlier studies proving that TVCL is a better predictor than the Bishop score, advocating for the inclusion of cervical ultrasound in regular obstetric practice. Secondly, the effectiveness of PGE₂ gel in cervical ripening and labor induction is also confirmed, further establishing its position as an ideal method for induction in women with an unfavorable cervix. Future research should explore individualized induction protocols incorporating maternal and fetal parameters to optimize labor outcomes.

This research points out the importance of transvaginal cervical length, Bishop score, and maternal parameters in determining the success of PGE₂ gel-induced labor. A cutoff cervical length of 2.65 cm was highly predictive of delivery outcomes, with decreasing lengths having a preference for vaginal delivery. Parity and BMI were also crucial factors, with multiparous women having greater rates of vaginal delivery and higher BMI being predictive of increased cesarean section likelihood. The effectiveness of PGE₂ gel in cervical ripening and induction of labor was reconfirmed, with the majority of women giving birth within 24 hours. Neonatal results were also positive, further endorsing the safety and efficacy of prostaglandin-induced methods. These results reaffirm the value of cervical ultrasound evaluation as a predictor and underscore the importance of individualized induction of labor plans to enhance maternal and neonatal outcomes.

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