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09 October 2024: Clinical Research  

Predicting Vaginal Delivery Success: Role of Intrapartum Transperineal Ultrasound Angle of Descent at a Single Center

Peby Maulina Lestari ORCID logo1ABEF*, Dindadikusuma 2ABCDEF, Ratih Krisna3ABEF, Theodorus 4ABF, Abarham Martadiansyah ORCID logo1DEF, Nuswil Bernolian ORCID logo1DEF, Putri Mirani ORCID logo1DEF, Muhammad Al Farisi Sutrisno ORCID logo2CDE, Bella Stevanny ORCID logo2CDEF

DOI: 10.12659/MSM.945458

Med Sci Monit 2024; 30:e945458

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Abstract

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BACKGROUND: Assessment of labor progress via digital vaginal examination is subjective, while intrapartum transperineal ultrasonography is deemed more objective and effective. The angle of descent (AoD) is a reliable intrapartum transperineal ultrasound parameter with minimal inter-observer and intra-observer errors. This study compared intrapartum transperineal ultrasonography with digital vaginal examination in evaluating the angle of descent for vaginal delivery selection in 70 women.

MATERIAL AND METHODS: This cross-sectional study was conducted at Dr. Mohammad Hoesin Hospital Palembang in Indonesia, using a consecutive sampling method to measure AoD of 70 patients at admission and every 2 h during labor progression. Patients were monitored until childbirth, and outcomes of successful vaginal or cesarean delivery were reported. A diagnostic test determined the optimal AoD for predicting successful vaginal delivery and its predictive value.

RESULTS: The study included 70 patients with a mean age of 28.29±6.09 years and a body mass index of 30.59±3.49 kg/m². Among them, 29 (41%) had successful vaginal deliveries. Adequate contraction frequency at admission was strongly associated with successful vaginal delivery (P<0.001). The optimal AoD for predicting successful vaginal delivery was 94.5°, with an area under the curve of 0.567 (95% CI 0.425-0.710), sensitivity of 84.2%, specificity of 45.7%, and accuracy of 54.3%.

CONCLUSIONS: Intrapartum transperineal ultrasonography for measuring AoD can be a valuable adjunct in labor management. Further investigations are needed to validate the optimal AoD in Indonesian pregnant women.

Keywords: Delivery, Obstetric, Labor, Obstetric, Predictive Value of Tests, Ultrasound, High-Intensity Focused, Transrectal

Introduction

The traditional evaluation of labor development is commonly performed by means of a digital vaginal examination. This assessment depends on regular vaginal examinations to evaluate the widening of the cervix and the downward movement of the baby’s head. Nevertheless, the clinical assessment of the descent station and fetal head position via vaginal examination is often inaccurate and subjective, particularly when palpating the caput succedaneum, located between the suture and fontanelle. Furthermore, the subjective evaluation of fetal head descent by periodic digital examination carries the risk of infection and maternal discomfort. The assessment of fetal head station descent relies on a hypothetical line connecting the 2 ischial spines. This evaluation can be challenging and often varies between theoretical concepts and clinical practice [1–4].

Ultrasound imaging is used as an adjunctive examination to evaluate fetal presentation in the maternal pelvis. Intrapartum transperineal ultrasonography provides clear benefits and exhibits greater efficacy, compared with digital vaginal examination [5–7]. The transperineal ultrasound examination measures 3 important parameters: head to symphysis distance, head to perineum distance, and angle of descent (AoD). Out of these parameters, AoD is regarded as very dependable because it has very little inter-observer and intra-observer variability [8]. AoD measurement using transperineal ultrasound provides an alternative method to predict successful vaginal delivery [9].

While noninvasive tests offer more comfort to patients, there are limitations, including operator dependency to obtain a good visualization of the angle in ultrasound images. Ultrasound readings have been assessed as potential indicators for predicting the outcome of vaginal birth. An essential characteristic that can be measured during the initial phase of labor is the AoD. The measurement is obtained with the use of a transperineal ultrasound and entails determining the angle formed by the long axis of the symphysis pubis and a line traced from its lower edge, which is tangent to the leading skull bone. This angle can be used to forecast the speed and probability of fetal head descent [10,11].

Out of the different ultrasound measurement techniques, the AoD shows good consistency and precision when evaluating the descent of the fetal head. In this review paper, we highlight the significance of examining the effectiveness of AoD in different phases of labor, as interventions vary in the context of abnormal labor. Assessing the AoD before labor can be helpful for counseling on when to induce labor. Additionally, a higher AoD value during the extended initial stage of labor has been shown to be associated with a higher likelihood of successful vaginal birth and a shorter time to delivery. During the second stage of labor, the AoD has demonstrated effectiveness in predicting the method of delivery and complex surgical deliveries. Moreover, it has aided in predicting the length of labor, therefore emphasizing its potential as a model for making decisions about the development of labor [12]. In India, research conducted by Malik et al [13] showed that an AoD with a possibility of successful vaginal delivery is greater than or equal to 116°. Similarly, in Egypt, research conducted by Solaiman et al [14] showed an AoD of 115° or higher is indicative of a successful spontaneous delivery in all pregnant women, regardless of the number of times they have given birth before. Frick et al [15] reported that the reliability of AoD measurements is higher when conducted by 2 operators rather than by a single operator.

The study conducted by Messina et al [16] compared the AoD measurement using transperineal ultrasounds during the initial stage of labor with digital vaginal examination. The study included 62 pregnant women who were at term and had a singleton fetus in cephalic presentation. The accuracy of vaginal examination in assessing fetal head station was found to be 34% when compared with the AoD measurement. Jung et al [12] also found that a wider angle of AoD is significantly associated with successful vaginal delivery.

Additional research is required to examine several elements of AOD, including the selection of cutoff values. This is necessary due to the complex interactions among maternal, fetal, and other contributing factors that determine the diverse characteristics of labor progression.

There is a scarcity of research on the AoD in Indonesia, mainly due to the infrequent use of intrapartum ultrasound examinations. Previous research by Simatupang et al [17] determined the ideal angle for predicting vaginal delivery in Jakarta to be 121°, while Saroyo et al [18] concluded that the optimal AoD for prediction of successful vaginal delivery in Karawang is 107°. The inconsistent findings from previous studies have prompted researchers to investigate the optimal AoD measured by intrapartum transperineal ultrasound examination to accurately predict the likelihood of successful vaginal delivery at our center, Dr. Mohammad Hoesin Hospital Palembang, as a main referral hospital in South Sumatra. Therefore, in this study, we aimed to compare intrapartum transperineal ultrasonography with digital vaginal examination to evaluate angle of descent in the selection of vaginal delivery in 70 women.

Material and Methods

INFORMED CONSENT AND ETHICS STATEMENT:

Written informed consent was obtained from each patient before their inclusion in the study. Ethical clearance from the Health Research Ethics Committee of Dr Mohammad Hoesin Hospital Palembang (96/kepkrsmh/2021) was obtained prior to the study, ensuring compliance with research ethics and regulations.

PATIENT SELECTION:

This study used a cross-sectional design with a consecutive sampling method and diagnostic test to determine the optimal AoD to predict successful vaginal delivery at Dr. Mohammad Hoesin Hospital Palembang. The minimum sample size, calculated using a confidence level of 95%, power level of 90%, and vaginal delivery prevalence rate of 80%, from Barbera et al [5], was 62 patients. To anticipate a 10% drop-out rate, we determined a minimum sample size of 68 patients. The study population included all parturient mothers scheduled for vaginal delivery at Dr. Mohammad Hoesin Hospital Palembang from September 2022 to June 2023 who met the predetermined inclusion and exclusion criteria. The study’s inclusion criteria were pregnant women in the gestational age between 37 and 42 weeks with a singleton fetus, cephalic presentation, and active labor progression who expressed willingness to participate by providing written informed consent. The exclusion criteria encompassed cases of cephalopelvic disproportion, macrosomic infants, and other findings requiring cesarean delivery. Matching techniques for maternal age, gestational age, and BMI were used to ensure homogeneity among the sample.

DATA COLLECTION:

Data collection encompassed a sequence of routine preliminary assessments and physical examination, followed by an intrapartum transperineal ultrasound examination for AoD measurement. The transperineal ultrasonography approach entailed positioning the probe between the labia below the pubic symphysis to obtain a sagittal view. Images were recorded during periods of rest between contractions, and the AoD was measured using either a goniometer or a conventional axis. The AoD measurement was taken between a line that passes through the middle of the pubic symphysis and a line that runs from the lowest point of the pubic symphysis to the fetal skull at a tangent (Figure 1). The AoD measurement was done at admission and every 2 h as the labor progressed. Patients were then monitored until childbirth, with reported outcomes that encompassed the mode of delivery. The data obtained were analyzed extensively, starting from preliminary study and inter-observer agreement testing, to determine the validity of measurements.

STATISTICAL ANALYSIS:

Statistical analyses were conducted using IBM SPSS Statistics version 24. A diagnostic test was used to determine the optimal AoD for successful vaginal delivery and its predictive value. Chi-square and Fisher exact tests were used to analyze categorical data, whereas the independent t test and Mann-Whitney U test were used to analyze numerical data.

Results

This study acquired a total of 70 patients, 29 (41%) of which successfully had a vaginal delivery. The maternal and fetal characteristics are presented in Tables 1 and 2. This study included parturient mothers with a mean age of 28.29±6.09 years and mean body mass index (BMI) of 30.59±3.49 kg/m2. Contractions of 2×/10′/30″ occurred most frequently (58.6%) at admission. Among fetal factors, umbilical cord entanglement was observed in 17.1% of cases, with an estimated fetal weight averaging 2852±530.33 g.

The patients were classified into 2 groups based on delivery mode: parturient mothers with successful vaginal delivery and those who had to undergo cesarean delivery. Maternal age, gestational age, and BMI were homogenous (P>0.05) between the 2 groups. Adequate contraction frequency at admission was strongly associated with successful vaginal delivery in this study (P<0.001). All mothers who experienced 4 contractions with 30-s duration every 10 min delivered vaginally, while those experiencing 2 contractions had to undergo cesarean delivery. Associations between each maternal factor and successful vaginal delivery are shown in Table 3.

We excluded cases of macrosomia. The estimated fetal weight was homogenous (P>0.05) between the 2 groups. However, all cases with previously undetected umbilical cord entanglement resulted in cesarean delivery. Associations between each fetal factor and successful vaginal delivery are shown in Table 4.

Table 5 shows the average duration of successful vaginal delivery was 5.58 h (4–7 h), significantly shorter than the 9.37 h (8–11 h) for cesarean delivery (P<0.001).

The optimal AoD to predict the likelihood of successful vaginal delivery in this study was determined to be 94.5° (Figure 2), with an area under the curve (AUC) of 0.567 (95% CI 0.425–0.710), sensitivity of 84.2%, specificity of 45.7%, and accuracy of 54.3%. Among patients with an AoD of ≥94.5°, 45.7% delivered vaginally. In contrast, only 37.1% of the patients with AoD of <94.5° delivered vaginally (Table 6).

Discussion

In this study, the average age of the patients was 28.29±6.09 years, ranging from 18 to 42 years. Li et al [19] also reported that the average age of pregnant women undergoing vaginal delivery was 28.83 years, which aligns with other studies reporting average maternal ages of 28.02 years in 2020 [20] and 26.7 years in 2016 [21] for vaginal deliveries. Women of advanced maternal age in the postpartum period are more likely to opt for cesarean delivery, due to concerns about fetal and maternal risks associated with frequent uterine contractions during normal labor. Furthermore, advanced maternal age is associated with an increased probability of encountering problems during childbirth, therefore making cesarean delivery a more secure option [21]

Statistical analysis revealed no differences in age, weight, height, BMI, or estimated fetal weight between pregnant women undergoing vaginal delivery and those undergoing cesarean section, suggesting that these factors did not influence the success of vaginal delivery in this study. However, there was a significant difference in contractions (P=0.000) between pregnant women undergoing vaginal delivery and those undergoing cesarean section. All pregnant women with contractions occurring 4 times per 10 min delivered vaginally, whereas all pregnant women with fewer contractions, occurring 2 times per 10 min, delivered via cesarean section. This finding is consistent with those of a study by Zagami et al [22] that reported a significantly higher frequency of contractions within 30 min in the vaginal delivery group (8.37±2.7) than in the cesarean delivery group (7.27±1.2; P=0.002). During the first stage of labor, uterine contractions increase in intensity from approximately 25 mmHg to 50 mmHg and persist until the end of labor. Simultaneously, there is an increase in frequency from 3 to 5 contractions every 10 min. Uterine contraction activity intensifies upon entering the second stage, augmented by maternal pushing efforts. Uterine contractions originate from myometrial activity, are vigorous, and last for a considerable duration, starting from the fundus area and spreading to the cervical region [23,24].

In the present study, all cases with previously undetected umbilical cord entanglement resulted in cesarean delivery. Among those who did not have umbilical cord entanglement, 29 out of 58 (50%) delivered vaginally. Guan et al [20] also reported a significant difference in umbilical cord entanglement between pregnant women undergoing vaginal delivery and those undergoing cesarean section (P<0.001). Umbilical cord entanglement is the main pathological condition observed in cases of umbilical cord anomalies and occurs in 14.7% to 33.7% of deliveries [25,26]. Previous studies have shown that umbilical cord entanglement can raise the likelihood of prolonged labor. However, it does not inevitably lead to an increased risk of cesarean section or instrumental delivery [26].

The AoD is the angle between the longitudinal axis created by the length of the pubic bone and the line drawn tangentially from the lowest prominence of the pubic bone to the deepest region of the fetal skull [27]. It is used to evaluate the occiput and fetal head position [5,13]. A vaginal delivery is consistently correlated with an angle of no less than 120°. Another study indicated that an AoD measurement of 125° has an 85% probability of resulting in a successful vaginal delivery [5,28]. Malik et al [13] reported an optimal AoD value, based on the receiver operating characteristic curve, to be 116°, with a sensitivity of 96.49% and specificity of 96.43% to predict successful vaginal delivery. However, in the present study, the optimal cutoff point for AoD with the best AUC value was found to be 94.5° to predict successful vaginal delivery in Dr. Mohammad Hoesin Hospital Palembang, with a sensitivity of 84.2% and specificity of 45.7%. This might be due to different sample characteristics and AoD measurement techniques between the studies.

To the best of our knowledge, this is one of the first studies to use AoD to predict successful vaginal delivery in Indonesia. The perineal intrapartum sonographic evaluation can be easily conducted by experienced physicians and midwives after a brief learning time. It is a good alternative to the invasive and less objective digital vaginal examination. We used matching techniques for maternal age, gestational age, and BMI to ensure homogeneity among the sample and reduce potential confounding factors. Furthermore, the data obtained were analyzed extensively, starting from preliminary study and inter-observer agreement testing to determine the validity of measurements. However, the data we have is primarily applicable to Indonesian women with a mean age of 18 to 42 years, BMI range of 25.00 to 38.70 kg/m2, and height range of 1.5 to 1.69 m. However, this study did not include women with labor arrest and labor induction. We also did not determine the number of previous vaginal deliveries. Moreover, this study was conducted at a single center and had a rather limited sample size, due to our limited funding and time allocated for conducting the research. Further research needs to be conducted with a larger sample in order to validate the optimal AoD for predicting successful vaginal delivery in Indonesian pregnant women.

Conclusions

Incorporating intrapartum transperineal ultrasonography to measure the AoD can be a valuable adjunct to labor management. The findings of this study indicate an optimal AoD of ≥94.5°, with 84.2% sensitivity and 45.7% specificity, to predict successful vaginal delivery at Dr Mohammad Hoesin Hospital Palembang. Further investigations need to be conducted to validate the optimal AoD in Indonesian pregnant women.

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