Labor is a clinical diagnosis, classically defined by the triad of regular painful uterine contractions, progressive cervical effacement and dilatation, and show (bloody discharge). Cervical dilatation in the absence of uterine contractions is seen most commonly in the second trimester and is suggestive of cervical insufficiency. Similarly, the presence of uterine contractions in the absence of cervical change does not meet criteria for the diagnosis of labor. Such contractions are often attributed to "false labor" or uterine irritability.1,2

Labour may be induced using medical methods (oxytocin or prostaglandins) or mechanical methods (extra amniotic balloon catheters or artificial rupture of membranes). The most common method in hospital practice worldwide are oxytocin and prostaglandins.3 Induction of labour in an unripe cervix is associated with frequent maternal complications and high rates of failure to the extent of 20-50% and caesarian delivery even when vaginal delivery is achieved these patients often have prolonged labour, with increased incidence of instrumental delivery and low APGAR.1

One of the important parameters in labour that determines the successful outcome is distance of the presenting part from the outlet. Traditionally, this is determined by the head distance either above or below the ischial spine, which is determined by per vaginal examination. However, digitally assessed head station during intrapartum period many times is inaccurate and not consistently reproducible by different examiners.4 the present study was focused on utilizing transperineal ultrasound to measure the fetal head to perineum distance, aiming to evaluate a novel and potentially superior predictor for successful normal delivery in induced labors.

Present study was single-center, prospective, observational study, conducted in department of Obstetrics & gynecology, at Government Multispecialty Hospital Sector 16, in Chandigarh, North India. Study duration was of 6 months (September 2023 to March 2024). Study was approved by institutional ethical committee.

Inclusion criteria

• Term singleton pregnancy with gestational age (>37) weeks, living fetus with vertex presentation, with poor bishop score ≤ 6, with reactive CTG, with intact amniotic membranes, underwent indication for medical induction of labor as (pre-eclampsia, diabetes, fetal Intrauterine Growth Restriction and oligohydramnios), willing to participate in present study

Exclusion criteria

• Favourable bishop score >6
• Multiple
• Rupture of
• Intrauterine fetal
• Contraindication for vaginal delivery like macrosomia (more than 4 KG), malpresentations, placenta previa, cord prolapse, vasa previa, uterine fibroids and active genital herpes.
•  
• Any sign of fetal distress as abnormal CTG or low biophysical
• History of scarred
•  

Study was explained to participants in local language & written informed consent was taken. Subsequently, the woman was positioned in the dorsal position with an empty bladder for a per-abdominal examination to assess the period of gestation, lie, presentation, and fetal heart rate. For digital vaginal examination, the patient was placed in the lithotomy position. During the examination, observations were made regarding the position of the cervix, its consistency, length, dilatation, and the station of the head, along with a pelvic assessment. The Bishop score was then calculated. Within 10 minutes, a transperineal ultrasound was performed to calculate the head-to-perineum distance. Following this, a transvaginal ultrasound was conducted to measure cervical length.

Subsequently, induction of labor was initiated, and fetal heart monitoring was carried out using a fetal doppler or cardiotocographic machine. The most common indication for a cesarean section after induction of labor was a non-reassuring fetal heart rate, with other indications including arrest of dilatation, second-stage arrest, cord prolapse, deep transverse arrest, and failed induction.

Means and proportions were calculated for continuous and categorical variables respectively. Difference in proportions were tested for statistical significance using chi square test. Difference in means between two variables were tested using independent sample t test. Sensitivity, specificity, and predictive values were calculated to measure the diagnostic accuracy. Correlation between two continuous variables was examined using Pearson correlation coefficient. A p value <0.05 was considered statistically significant.

Among 200 subjects, majority of participants fall within the 18-25 age (43.5%) followed by age group is 26-30 (37 %). Nearly half of the participants, constituting 47.5%, fall into the BMI category of less than 25, indicating a normal weight range. Primiparous individuals, those experiencing their first childbirth, constitute the majority of the participants (59.0%). Among those who did report personal health history, 12.0% indicated a history of hypothyroidism (12 %), Anemia (1 %), asthma (0.5 %), and epilepsy (0.5 %).

Table 1: General characteristics

The highest percentage of participants, had a gestational age of 41 weeks (27 %), followed by 38 weeks (26 %) and 37 weeks (21 %). On USG, highest percentage of participants had a gestational age of 37 weeks (25.5%), followed by at 39 weeks (22 %) and at 38 weeks (21 %).

Table 2: Based on gestational age as per LMP & USG (n=200)

Postdatism emerges as the most common indication (32.5 %), followed by IHCP (Intrahepatic Cholestasis of Pregnancy) (27.5%). Other notable indications include FGR (Fetal Growth Restriction) with 9.0%, Gestational HTN (Hypertension) with 9.5%, and Oligohydramnios with 8.0%.

Table 3: Indication for induction of labour (n=200)

The highest frequency of participants, at 37.5%, had a score of 2, followed by 33.5% with a score of 3. Scores of 1, 4, and 5 were reported by 12.0%, 12.5%, and 4.5% of participants, respectively.

Table 4: Distribution of study participants based on modified BISHOPS score

The highest percentage of participants, at 43.0%, experienced labour lasting between 19 and 24 hours. The next most prevalent duration was 13-18 hours, accounting for 30.5% of participants. Labor lasting 24-30 hours was reported by 21.0% of participants, and labour lasting up to 12 hours was reported by 5.5% of participants.

Table 5: Distribution of study participants based on duration of labour

The majority of participants, constituting 71.0% of the total sample, underwent Vaginal Delivery. Caesarean Delivery was the mode of delivery for 29.0% of participants. Among the participants, the most prevalent indication for Caesarean section was fetal distress (39.7%), others were failed induction (10.3%), meconium- stained liquor with fetal distress (MSL with FD) (18.9%) & Non-Progress of Labour (NPOL) (31%). .

Table 6: Distribution of study participants based on mode of delivery (n=200)

The most common birth weight range is 2.5-2.99 Kg (40 %) followed by 3.0-3.49 Kg (36 %) and 2.0-2.49 Kg (11 %).

Table 7: Distribution of study participants based on birth weight (n=200)

The mean head to perineum distance for Vaginal Delivery is 59.31 ± 7.84 mm, while for Caesarean Delivery, the mean is 66.57 ± 6.02 mm, a statistically significant difference (p < 0.001) was noted. This indicates that there is a significant difference in the head to perineum distance between participants who underwent Vaginal Delivery and those who underwent Caesarean Delivery.

The mean cervical length for Vaginal Delivery is 30.70 ± 4.12 mm, while for Caesarean Delivery, the mean is 35.62 ± 4.75 mm, a statistically significant difference (p < 0.001). was noted. This indicates a significant difference in cervical length between participants who underwent Vaginal Delivery and those who underwent Caesarean Delivery.

Table 8: Distribution of study participants based on mode of delivery

AUC analysis suggests that the USG Head to Perineum Distance is a statistically significant and reasonably accurate measure.

Sensitivity for predicting vaginal delivery when Head to Perineum Distance is greater than 58 mm is 89.66%. Specificity for predicting Caesarean delivery when Head to Perineum Distance is 58 mm or less is 47.18%. Positive Predictive Value (PPV) was 40.94%. Negative Predictive Value (NPV) was 91.78%. The overall accuracy of the test is 59.50%.

Table 9: Predictive accuracy head to perineum distance on USG for vaginal delivery

AUC analysis suggests that Cervical Length is a statistically significant and reasonably accurate measure.

Sensitivity for predicting vaginal delivery when cervical length is greater than 30 mm is 84.48%. Specificity for predicting Caesarean delivery when cervical length is 30 mm or less is 51.41%. Positive Predictive Value (PPV) was 41.53%. Negative Predictive Value (NPV) was 89.02%. The overall accuracy of the test was 61.00%.

Table 10: Predictive accuracy head to cervical length on USG for vaginal delivery (n-200)

Modified Bishop’s Score: With a cut-off value of 3, it demonstrates high sensitivity (94.83%) but relatively low specificity (21.83%). The positive predictive value (PPV) is 33.13%, indicating the probability of a caesarean delivery given a positive test result, while the negative predictive value (NPV) is 91.18%. The accuracy is 43.00%.

Fetal Head to Perineum Distance: Using a cut-off of 58 mm, this parameter shows slightly lower sensitivity (89.66%) but improved specificity (47.18%) compared to the Modified Bishop’s Score. The PPV is 40.94%, NPV is 91.78%, and accuracy is 59.50%.

Cervical Length: With a cut-off value of 30 mm, cervical length demonstrates sensitivity of 84.48% and specificity of 51.41%. The PPV is 41.53%, NPV is 89.02%, and accuracy is 61.00%.

Table 11: Diagnostic accuracy of the studied predictive parameters in determining successful vaginal delivery

There is a clear association between head to perineum distance and the mode of delivery. As head to perineum distance increases, there is a shift from a higher proportion of Vaginal Deliveries to a higher proportion of Caesarean deliveries. The p value less than 0.001 suggests that the observed differences in proportions across head to perineum distance categories are statistically significant.

Table 12: Association between head to perineum distance and mode of delivery

* Chi Square test was applied to test statistical difference in proportions

There is a significant association between cervical length and the mode of delivery. As cervical length increases, there is a shift from a higher proportion of Vaginal Deliveries to a higher proportion of Caesarean Deliveries. The p value less than 0.001 suggests that the observed differences in proportions across cervical length categories are statistically significant.

Table 12: Association between cervical length and mode of delivery (n = 200)

* Chi Square test was applied to test statistical difference in proportions

Cervical Length p-value is 0.000, indicating that cervical length is a statistically significant predictor of head to perineum distance. The odds ratio is 1.411, with a 95% confidence interval between 1.253 and 1.589. The significant p-value for Cervical Length implies that it is a statistically significant predictor of head to perineum distance, while other factors in the model do not show statistical significance.

Table 13: Multivariate logistic regression analysis to determine maternal factors influencing head to perineum distance

In today’s current scenario USG examination conducted before onset of labour has emerged as a valuable tool for obstetricians in formulating an appropriate labour plan. The widespread availability of ultrasound machines in contemporary healthcare settings, coupled with their safety, non-invasiveness, simplicity, and ease of use, makes them an accessible and convenient option. The selection of an inappropriate candidate for vaginal delivery is a crucial factor contributing to the failure of induction. With the rising prevalence of abdominal deliveries over the years and failure of descent ranking as the second most common indication for cesarean section, there is a pressing need to assess a method for predicting successful vaginal delivery.

Ultrasound examination conducted before the onset of labor has emerged as a valuable tool for obstetricians in formulating an appropriate labor plan. The parameters obtained through ultrasound examination can be efficiently recorded and analyzed. Growing evidence supports the utility of transperineal ultrasound in estimating fetal head–perineum distance (FHPD) as a predictive measure for the success of labor induction. Notably, the procedure is characterized by minimal time consumption, a rapid learning curve, and ease of mastery.

In our study, the participants' age distribution reveals a majority in the 18-25 age range (43.5%), followed by 26-30 (37.0%). These findings are consistent with the studies conducted by Ali et al.,5 Khazardoost et al.,6 and Dasgupta et al.,7 which also reported a younger participant population. Ali et al.,5 observed that 74.9% of their participants were primigravida, reflecting a relatively young age, while Khazardoost et al.,6 reported a mean age of 25.1 years. Dasgupta et al.,7 noted a mean age of 23.99 years, reinforcing the trend of younger participants in studies exploring induction of labor.

Our study reveals a substantial proportion of primiparous participants (59.0%), consistent with the findings of Ali et al.,5 who reported 74.9% primigravida. El-Bishry et al.,8 also reported a majority of primigravidae (75.6%) among their participants. These consistent patterns across studies suggest a common focus on the obstetric outcomes of women experiencing their first childbirth, acknowledging the unique challenges associated with primiparity.

The gestational age analysis both by LMP and USG highlighted a peak at 41 weeks (27% and 25.5%) respectively. The gestational age distribution in our study, asper both LMP and USG, aligns with the physiological range for term pregnancies. The predominant gestational age in both measures is consistent with findings from Gebreil et al.,8 El-Bishry et al.,8 and Richa et al.,10 indicating a focus on full-term pregnancies in studies evaluating induction outcomes.

The most common indication for induction in our study was postdatism (32.5%), aligning with the findings of Khazardoost et al.,6 and Dasgupta et al.,7 emphasizing the prevalence of post-term pregnancies as a primary trigger for induction. The distribution of other indications, such as hypertensive disorders, intrahepatic cholestasis, and fetal growth restriction, varies among studies, highlighting the diversity of patient populations and regional healthcare practices.

In the context of predicting the mode of delivery, this study demonstrates a significant association between cervical length and the likelihood of Caesarean delivery, evidenced by an AUC of 0.7709, significantly higher than the findings of Vinutha MB et al.,11 where the AUC was only 0.534 and not statistically significant. This discrepancy underscores the potential variability in predictive power of cervical length across different populations or methodologies. Conversely, our results are more aligned with those of Sinha et al.,12 who reported a higher AUC of 0.857, further reinforcing the notion that cervical length is a critical predictor of delivery mode.

In our study, the fetal head-perineum distance (HPD) plays a pivotal role, with a specific cutoff identified (<5.5 cm) for predicting successful vaginal delivery. This aligns with the emphasis placed on HPD in other studies. Dasgupta et al.,7 reported a mean fetal HPD by transperineal ultrasound of 3.92 cm, indicating a consistent focus on the relevance of this parameter across different research contexts. Gebreil et al.,9 also considered HPD (mean 5.17 cm) as part of their evaluation, further supporting the significance of this metric in predicting induction outcomes.

In our study examining the predictive value of Fetal Head-Perineum Distance (FHPD) in the induction of labor (IOL), we identified a FHPD cutoff of <5.5 cm, demonstrating robust predictability for successful vaginal delivery, with a sensitivity of 97% and specificity of 88.1%. These findings align with and contribute to the existing body of literature on this topic.6,11,13 The optimal application of FHPD in clinical practice requires a nuanced understanding of its strengths and limitations. Our study, combined with insights from comparative studies, emphasizes the potential of FHPD as a reliable predictor, particularly in scenarios where other parameters may be inconclusive. However, the lack of standardized cutoff values and the influence of demographic and baseline characteristics necessitate cautious interpretation.

Taking into account the cost-effectiveness and decreased variability between observers associated with ultrasound measurements,14,15,16,17,18 we propose the routine utilization of this measurement tool for labor monitoring. Previous research19,20,21 has already established the enhanced predictive value of cervical length measured through trans-vaginal ultrasound in comparison to the Bishop Score. Nevertheless, given that trans-vaginal ultrasound involves the placement of a vaginal probe, the translabial ultrasound emerges as a more well-tolerated and widely accepted alternative among most women.

This approach is secure, non-intrusive, and furnishes valuable objective metrics for predicting the appropriateness of labor induction. The acceptance of translabial ultrasound by women is likely to be higher, particularly when contrasting it with the discomfort associated with evaluating the Bishop Score. Furthermore, the diminished infection risk, especially in scenarios involving amniotic sac rupture, underscores the recommendation for the routine utilization of translabial ultrasound in monitoring labor progression.

Based on these considerations, even though there is limited data available, a dynamic transperineal ultrasound assessment appears to be more fitting for predicting labor outcomes than a static assessment. Nevertheless, the alterations in ultrasound parameters during contractions are not routinely quantified in clinical practice.

Strengths of present study were, the study has a substantial number of participants, potentially enhancing the generalizability of the findings to a broader population. The study incorporates various parameters such as fetal head to perineum distance, maternal factors, Bishop Score, and ultrasound measurement of cervical length. This comprehensive approach increases the depth of the analysis and provides a more holistic understanding of the factors influencing labor induction outcomes.

Limitations of present study were, the use of convenient sampling might introduce selection bias, as participants may not be entirely representative of the broader population. This could affect the external validity of the study. The measurement of variables such as Bishop Score and ultrasound parameters involves subjective assessments. Observer bias might affect the reliability and reproducibility of these measurements.

The study underscored the significant relationship between the mode of delivery and key metrics and highlighting the pre-induction head-to-perineum distance, thereby illuminating their predictive value. The measurement of fetal head-to-perineum distance using transperineal ultrasound emerges as a straightforward, non-invasive technique for forecasting the success of labor induction. This method can serve as a supplementary tool, enhancing the information gained from a per vaginal examination. By leveraging ultrasound imagery, healthcare professionals can offer more informed counselling to patients prior to induction of labor, effectively communicating the likelihood of induction success.

Conflict of Interest: None to declare

Source of funding: Nil

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