Childbirth is one of the most significant physiological events in a woman’s life. Vaginal delivery has traditionally been the preferred mode of birth due to its numerous maternal and neonatal benefits. Vaginal delivery offers maternal advantages such as faster recovery, shorter hospital stays, reduced risk of complications, reduced costs, and better future reproductive outcomes [1]. The advantages for neonates born from vaginal delivery include improved respiratory system adaptation and enhanced immune system development. However, with these advantages, vaginal delivery can be associated with risks such as perineal tear, pelvic floor dysfunction, prolonged labor, and neonatal birth injuries [2]. Cesarean section is done in those cases where vaginal delivery is not possible for any reason. Conversely, it is linked with the intraoperative and postoperative complications such as hemorrhage, infection, thromboembolism, neonatal respiratory complications, and also increased risks during the subsequent pregnancies, including placenta previa, placenta accreta, uterine rupture, adhesions, and repeat cesarean delivery [3]. As the rates of cesarean delivery continue to increase across the world, issues of excessive application of surgical delivery have arisen. The World Health Organization (WHO) has suggested that the rate of cesarean section must not be higher than 10-15% of any population because unnecessary surgical delivery poses a substantial risk to mother and child [4]. The induction of labor is now a common procedure in obstetric practice because of various maternal and fetal indications. This included post-term pregnancy, hypertensive disorders, and fetal growth restriction, etc. The major challenge in obstetric practice is the prediction of successful vaginal birth, particularly in women undergoing labor induction. While induction is a common procedure, it may not always be successful, and its failure can result in maternal morbidity or may lead to cesarean birth and increased complications in subsequent pregnancies [5]. Usually, the cervical readiness for labor is determined by the applying Bishop score. Since the Bishop Score is subjective, inconsistencies among the clinicians have been noted with a low predictive value, with reported sensitivities of between 24%-64% [6]. These limitations have led to a desire to have a more objective and reliable approach to the prediction of a successful vaginal delivery. Advancements in ultrasound-based assessments have important applications in obstetric imaging. It has now emerged as an excellent alternative. Ultrasonography parameters such as cervical length, fetal head descent, and fetal head to perineum distance (FHPD) provide an objective assessment of labor progress [7]. Fetal head perineum distance is one of the parameters used, being a non-invasive, simple, and repeatable estimator, as it is an indicator of head engagement and descent of the fetus, which is an important factor of successful vaginal birth. With this background, we in the current study aimed to evaluate the role of ultrasonographically measured fetal head–perineum distance prior to induction of labor as a predictor of successful vaginal delivery. And to gather evidence-based data as a predictor of successful vaginal delivery and compare the values with Bishop’s score.

This prospective observation and comparative study was done in the CKM Government Maternity Hospital, Warangal, Telangana, from April 2023 to October 2024. Institutional Ethical approval was obtained for the study. Written consent was obtained from all the participants of the study after explaining the nature of the study in the vernacular language. Inclusion Criteria 1. Pregnant women at ≥ 37 weeks of gestation undergoing labor induction. 2. Nulliparous women with a singleton pregnancy in cephalic presentation. 3. No known fetal anomalies or pregnancy complications affecting labor. Exclusion Criteria 1. Previous cesarean section or uterine surgery. 2. Fetal malpresentation (breech, transverse, etc.). 3. Multiple pregnancy or major congenital fetal anomalies. 4. Maternal medical conditions contraindicate vaginal delivery. Sample size calculation: The Formula for calculating the sample size used was n = (Z² × P × (1 – P)) / d² Where: Z = Z-score (for 95 % confidence interval, Z = 1.96), P = expected proportion of success (e.g., vaginal delivery = 0.70 based on previous studies), d = margin of error (assumed = 0.10 or 10 %) Substituting values: n = (1.96² × 0.70 × 0.30) / 0.10² n = (3.8416 × 0.21) / 0.01 n = 0.8067 / 0.01 n = 80.67 Since the calculated sample size is n = 80.67, and to account for possible dropouts, we round up to 100 participants. Data collection was done by Pre-Induction Assessment and Ultrasound Examination, which included the Fetal Head-Perineum Distance (FHPD) measured transperineally. The Angle of Progression (AOP) and Cervical Length (CL) recording is given in Figure 1. Bishop Score was used to assess the cervical condition and the station of the head to choose the best method for induction. Consists of 5 parameters: cervical dilatation, length, consistency, position, and station of the head. Total possible score = 13. Table 1: Assessment using Bishop’s score Parameter 0 points 1 point 2 points 3 points Cervical dilatation Closed 1–2 cm 3–4 cm ≥ 5 cm Cervical length > 2 cm 2–1 cm 1–0.5 cm < 0.5 cm Cervical consistency Firm Medium Soft — Cervical position Posterior Central Anterior — Station of the head −3 −2 −1 / 0 +1 / +2 (below ischial spines) Labor Induction Protocol: Prostaglandin E2 (PGE2) or oxytocin used was based on hospital guidelines. Continuous fetal heart rate monitoring during labor. Delivery Outcome Measures: Successful Vaginal Delivery vs. Cesarean Section. Time from induction to delivery. Neonatal outcomes (Apgar score, NICU admission, birth weight, complications). Expected Outcome: Determining whether FHPD is a better predictor of vaginal delivery success compared to the Bishop Score. Providing objective, ultrasound-based labor assessment guidelines to reduce unnecessary cesarean sections. Statistical Analysis: All the available data were refined, segregated, and uploaded to an MS Excel spreadsheet and analyzed by SPSS version 26 in Windows format. Descriptive Statistics were represented as mean ± SD, frequency, and percentage for continuous variables. Categorical data was calculated by application of the Chi-square test to compare vaginal vs. cesarean delivery outcomes. The P-value < 0.05 is considered statistically significant.

A total of 100 primigravida women were studied during this research. The baseline characteristics of the study population are given in Table 2. The age range of women in this study was 18 to 35 years, with the mean age of 25.6 ± 3.4 years, which is the common reproductive age for women. The mean height of the cohort was 156.8 ± 5.2 cm, and the mean weight was 62.1 ± 7.8 kg. The mean BMI of the cohort was 25.4 ± 3.2 kg/m², which showed that most of the women in this study were of the overweight category. All the women were primigravida with singleton pregnancy and cephalic presentation, which indicated a homogeneous study population. Pre-induction assessment showed a relatively low mean Bishop score of 4.2 ± 1.3, suggesting an unfavorable cervix in many participants. The mean fetal head–perineum distance (FHPD) measured by ultrasound was 5.2 ± 0.9 cm. All cases had a reactive non-stress test, confirming a reassuring fetal status before induction. Table 2: Baseline characteristics of the study population Characteristic Mean ± SD (Range) / n(%) Maternal characteristics Age in years 25.6 ± 3.4 (18 – 35) Height in cms 156.8 ± 5.2 (145 – 170) Weight in Kg 62.1 ± 7.8 (50 – 85) BMI in Kg/m2 25.4 ± 3.2 (19.0 – 32.0) Parity (Primigravida) 100 (100%) Pregnancy Details Gestational age (Weeks) 38.9 ± 1.1 (37 – 40) Presentation (Cephalic) 100 (100%) Estimated fetal weight (Kg) 2.9 ± 0.4 (2.5 – 3.8) Pre-Induction Assessments Bishop score 4.2 ± 1.3 (2-7) Fetal Head-perineum distance (FHPD in cms) 5.2 ± 0.9 (3-7) Reactive Non-stress test (NST) 100 (100%) Distribution of key predictive indices is presented in Table 3. A critical analysis of the table showed that the common indication for LSCS was fetal distress in 55.6% of cases. Non-progression of labour was in 30.6% cases, and failed induction in 13.9% of cases. Neonatal outcomes (NICU) admissions in the NVD group were 3.1% and in the LSCS group, neonates were 19.4% the values were found to be statistically significant. The neonatal outcomes in this study showed that NICU admissions were higher in the LSCS group (19.4%) as compared to the NVD group (3.1%), which is an indication of adverse outcomes related to LSCS. The differences were calculated to be statistically significant. Table 3: Distribution of Key Predictive Indices Before Induction Parameter Category n (%) Bishop Score 3 (Unfavorable) 20 (20%) 4 — 5 (Moderate) 58 (58%) 2 6 (Favorable) 22 (22%) Fetal Head-perineum Distance (FHPD) 5.5 cm 64 (64%) > 5.5 cm 36 (36%) Body Mass Index (BMI) Normal (19—24.9 kg/m2) 45 (45%) Overweight (25—29.9 kg/m2) 40 (40%) Obese (> 30 kg/m2) 15 (15%) Association of predictive indices with mode of delivery is given in Table 4. Analysis of the table showed that Bishop score and FHPD were strongly associated with mode of delivery. Women with a Bishop score ≥ 6 had significantly higher rates of vaginal delivery (92%), as compared to those with a Bishop score ≤ 3, who had significantly higher chances of LSCS (70%). The values of FHPD also showed strong prediction of mode of delivery, with women with FHPD ≤ 5.5 cm delivered vaginally in 87.5% and women with FHPD ≥ 5.5 cm, 77.8% required LSCS. This showed that a shorter fetal head–perineum distance is strongly associated with successful vaginal delivery, reinforcing its role as a reliable sonographic predictor. Table 4: Association of Predictive Indices with Mode of Delivery Predictor Category Vaginal Delivery (NVD) n (%) Cesarean Section (LSCS) n (%) Bishop Score 3 6 (30.0) 14 (70.0) 4 - 5 35 (63.6) 20 (36.7) ≥ 6 23 (92.0) 2 (8.0) FHPD (cm) ≤ 5.5 56 (87.5) 8 (12.5) ≥ 5.5 8 (22.2) 28 (77.8) Association of maternal BMI with mode of delivery is given in Table 5. Vaginal delivery rates were highest among women with normal BMI (84.4%), followed by overweight women (50%). In contrast, 60% of obese women required LSCS, suggesting an inverse relationship between increasing BMI and the likelihood of vaginal delivery. This finding indicates that higher maternal BMI is associated with increased cesarean section rates. Table 5: Association of Maternal Body Mass Index (BMI) with Mode of Delivery BMI Category Vaginal Delivery (NVD) n (%) Cesarean Section (LSCS) n (%) Total Normal (19—24.9 kg/m2) 38 (84.4) 7 (15.6) 45 Overweight (25—29.9 kg/m2) 20 (50.0) 20 (50.0) 40 Obese (230 kg/m2) 6 (40.0) 9 (60.0) 15 Total 64 36 100 Predictive accuracy of the bishop score and FHPD is depicted in Table 6. The analysis of the table showed that a Bishop score ≥ 4 demonstrated high sensitivity (90.6%) for vaginal delivery, while its specificity was lower at 38.9%, indicating that the ability to exclude those who require LSCS is limited. Similarly, the FHPD ≤ 5.5 cm had a high sensitivity of 87.5%, and high specificity (77.8%), and the overall accuracy was 84% which showed that it was superior to Bishop's score. This finding indicated that the ultrasound measurement of FHPD appears to be a more reliable and objective predictor of successful vaginal delivery than traditional Bishop scores. Table 6: Predictive Accuracy of Bishop Score and FHPD for Successful Vaginal Delivery Predictor & Cut-off Sensitivity (%) Specificity (%) Positive Predictive Value (PPV) (%) Negative Predictive Value (NPV) (%) Accuracy Bishop Score ≥ 4 (for predicting NVD) 90.6 (58/64) 38.9 (14/36) 76.3 (58/76) 66.7 (14/21) 72.0 (72/100) FHPD ≤ 5.5 cm (for predicting NVD) 87.5 (56/64) 77.8 (28/36) 87.5 (56/64) 77.8 (28/36) 84.0 (84/100)

Induction of labour is a widely used procedure in obstetric practice. Accurate prediction of successful vaginal delivery is important for risk minimization and reducing unnecessary cesarean sections, which are sometimes associated with maternal and fetal morbidity. The current study aimed to determine the predictive ability of ultrasound-measured fetal head perineum distance (FHPD) as an objective predictor of successful vaginal delivery before labour induction and compare its predictive validity with that of the Bishop’s score. The mean maternal age of the cohort was 25.6 ± 3.4 years in this study. This is the normal reproductive age group as per other previous studies that have estimated the labour outcomes among primigravida women (8,9). The study population was also homogeneous in the sense that it only involved primigravida women with singleton, term, cephalic pregnancies, and, in effect, this reduced the confounding factors concerning parity and malpresentation. The average Bishop score of 4.2 ± 1.3 showed that most of the women were not favorable at the time of induction, a situation that is a common occurrence in clinical practice (10). The overall vaginal delivery rate of 64% in the current study is comparable to the previous studies that had assessed the outcome of the induction in the primigravida women (11,12). Out of the cesarean births, fetal distress was in (55.6%) cases, and it was the most common sign, followed by non-progression of labour and failed induction, which is in line with the existing literature (13). Notably, the neonatal outcomes showed much better results of high NICU admissions in the LSCS group (19.4% vs 3.1% in the vaginal delivery group), which indicates the clinical significance of enhancing the predictability of a successful vaginal delivery to minimize operative procedures (14). One of the major findings of the study was a close correlation between mode of delivery and FHPD. The vaginal delivery rate was significantly higher in women with FHPD ≤ 5.5 cm and lower (77.8%) in women with FHPD≥ 5.5 cm. This confirms the hypothesis that the shorter the fetus's head-to-perineum distance, the more indicative of increased engagement of the fetus's head and favourable pelvic dynamics, which increases the chances of successful vaginal delivery. Similar findings have been reported by other authors, like Eggebo et al., who also found that sonographic parameters, which measure fetal head position and descent, are effective predictors of labour outcome (15,16). FHPD was found to have a high predictive accuracy compared to the Bishop score. At Bishop score that was ≥ 4, high sensitivity (90.6%) was exhibited, whereas its specificity was poor (38.9%), thereby limiting its ability to predict failed vaginal delivery. Conversely, FHPD ≤ 5.5 cm and below had good sensitivity (87.5%) and specificity (77.8%) with a total accuracy of 84%. This demonstrates that it has better discriminative ability. This is in line with past research, which has indicated that the ultrasound measurements present more objective and reproducible results compared to the digital cervical examination (17,18). There was also an effect of maternal BMI on delivery outcomes, whereby high rates of cesarean delivery were recorded in the obese women. This observation is in line with the available evidence that has pointed towards the relationship between the maternal BMI and the length of labour with the rates of operative births (19). The results of the present study indicated that ultrasound evaluation of FHPD before labor induction appears to be a valid, objective, and useful clinical predictor for vaginal birth as compared to the traditional Bishop scores. Therefore, evaluation of FHPD must be done for pre-induction analysis to maximize material and neonatal outcomes.

The results of the study showed that ultrasound assessment of fetal head-perineum distance (FHPD) prior to induction is a reliable indicator of successful vaginal delivery in primigravida. It was found that a score of (≤ 5.5 cm) was strongly associated with higher rates of normal vaginal delivery, which was better than the Bishop score, which showed limited specificity. It was also found that the body mass index influenced delivery outcomes, with a higher rate of cesarean in obese women. Therefore, routine use of FHPD in pre-induction evaluation may improve clinical decision-making and reduce unnecessary cesarean sections for better maternal and neonatal outcomes.

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