Impact of intrapartum ultrasound on mode of delivery guidance and adverse pregnancy outcomes in primigravidae undergoing vaginal trial labor

Abstract

Objective

This study aims to analyze the impact of intrapartum ultrasound on mode of delivery guidance and the occurrence of adverse pregnancy outcomes in primigravidae undergoing a vaginal trial of labor.

Methods

A total of 200 primigravidae admitted to our hospital from January 2021 to December 2022 were included as the subjects of this study. They were randomly divided into a control group and a study group, with 100 cases in each group. The control group underwent the vaginal finger test, while the study group underwent a combination of the vaginal finger test and intrapartum ultrasound. The consistency between the vaginal finger test and intrapartum ultrasound in determining fetal position was evaluated in the study group, and the mode of delivery and pregnancy outcomes were compared between the two groups.

Results

The consistency of fetal occiput position between ultrasound and vaginal finger examination in the study group was 54.5% for occiput anterior position, 46.1% for occiput posterior position, and 31.4% for occiput transverse position, with an overall consistency of 46.5%. There was no significant difference in the cesarean section rate between the two groups. The rate of vaginal delivery in the control group was significantly lower than that in the study group, while the rate of perineal laceration was significantly higher in the control group. There were no significant differences in adverse outcomes for mothers and newborns between the two groups. The Angle of Progression (AOP) during natural vaginal delivery was significantly higher than that in other delivery modes, while AOP in cesarean section was significantly lower than that in other delivery modes. The head–perineum distance (HPD) during natural vaginal delivery was significantly lower than that in other delivery modes, while HPD in cesarean section was significantly higher than that in other delivery modes.

Conclusion

Intrapartum ultrasound serves as an important adjunct in a vaginal trial of labor for primigravidae, aiding healthcare providers in accurately determining fetal head position, reducing the rate of perineal laceration, and increasing the rate of vaginal delivery. Notably, there are significant differences in ultrasound findings between women undergoing natural vaginal delivery and those with other delivery modes.

What does this study add to the clinical work?

Intrapartum ultrasound improves the accuracy of fetal head position assessment during vaginal trial of labor in primigravidae and is associated with a higher vaginal delivery rate and lower perineal laceration rate. Ultrasound parameters, particularly Angle of Progression and Head Perineum Distance, may also help predict delivery mode outcomes.

Introduction

Regular vaginal examinations are essential during labor to assess labor progression, detect deviations from normal progression, and facilitate early intervention, thereby reducing the risk of adverse maternal and fetal outcomes [1]. The National Institute for Health and Clinical Excellence (NICE) and the World Health Organization (WHO) recommend vaginal examinations every 4 h [2]. However, the accuracy of vaginal examinations, specifically in determining fetal head position, is often suboptimal. Studies have indicated that vaginal examinations inaccurately predict fetal head position in 20–40% of laboring women, irrespective of the examiner’s experience. Particularly, the accuracy of vaginal palpation for posterior occipital and transverse positions is only around 50% [3, 4]. Furthermore, vaginal examinations carry an increased risk of infection [5].

Ultrasonography has emerged as an indispensable tool in clinical diagnosis due to its safety, noninvasiveness, ease of use, and provision of reliable data for disease diagnosis. Intrapartum ultrasound, a non-invasive, rapid, and accurate method, is extensively utilized for assessing fetal and maternal conditions during labor [6]. Vaginal trial of labor may present unfavorable factors that could contribute to adverse pregnancy outcomes postpartum, such as fetal distress, brachial nerve pain, and perineal tears. Real-time ultrasound monitoring during labor enables timely identification of these risk factors, facilitating appropriate interventions and effectively reducing the incidence of adverse postpartum outcomes [7]. Intrapartum ultrasound allows healthcare providers to observe the fetus in real time, including its position, size, and amniotic fluid volume, facilitating a more precise assessment of delivery feasibility and enabling personalized delivery plans [8]. For women with favorable fetal status and a suitable birth canal for vaginal delivery, intrapartum ultrasound serves to confirm and guide natural delivery. Conversely, for women at risk of obstructed labor, intrapartum ultrasound provides timely recommendations for manual interventions, such as instrumental delivery or cesarean section [9].

Thus, the application of intrapartum ultrasound in a vaginal trial of labor for primigravid women contributes positively to guiding the mode of delivery and improving adverse pregnancy outcomes postpartum. This paper aims to discuss the impact of intrapartum ultrasound on delivery mode guidance and the incidence of adverse postpartum pregnancy outcomes in primigravid women undergoing a vaginal trial of labor, as well as its clinical application.

Participants and methods

Participants

A total of 200 cases of primigravid women who were clinically admitted to our hospital between January 2021 and December 2022 were included as subjects in this study. The subjects were randomly assigned to either the control group or the study group, with 100 cases in each group, using the random number table method. The study protocol was reviewed and approved by the Ethics Committee of our hospital, and all procedures were conducted in compliance with the ethical guidelines outlined in the Declaration of Helsinki for clinical research. Informed consent was obtained from the mothers and their families, and written informed consent forms were signed prior to the enrollment of all subjects.

Inclusion and exclusion criteria

Inclusion criteria:

• Gestational age is between 37 and 40 weeks, indicating full-term delivery.

• Primigravid women with singleton pregnancies.

• Assessment of suitability for a transvaginal trial of labor conducted prior to delivery.

• Absence of pregnancy-related comorbidities and complications.

• Conception occurred naturally.

Exclusion criteria:

• Fetal developmental abnormalities or chromosomal abnormalities.

• Pregnancy-related comorbidities, including pre-eclampsia, hypertension requiring anti-hypertensive medication, diabetes mellitus, renal disorders, or autoimmune disorders.

• History of previous uterine surgery, such as myomectomy.

• Body mass index (BMI) exceeding 50 kg/m² or estimated fetal weight exceeding 5 kg.

• Pre-existing comorbidities of heart disease, epilepsy, or bleeding disorders prior to pregnancy.

Assessment methods

Vaginal finger examination

The control group used the traditional method of vaginal finger examination to assess the progress of labor. The specific procedure is as follows: The mother assumes a supine or prone position with flexed and separated legs. After perineal disinfection, the operator wears sterile gloves and applies an appropriate amount of lubricant to the examining finger. During the examination, the operator uses the thumb and forefinger of the assisting hand to separate the labia majora and minora, fully exposing the vaginal opening. In the contraction phase, the examining hand’s forefinger or one of the middle fingers is gradually inserted into the vagina. After reaching a depth of 3–4 cm, the finger is turned upwards to assess the cervix, vagina, fornix, and pelvis. Care is taken to avoid excessive force during insertion to prevent discomfort or injury. Once the finger is inside the vagina, the healthcare provider gently rotates it to assess the degree of cervical dilation and firmness. The healthcare professional records the degree of cervical dilation based on the examination findings. The knuckle system is commonly used to indicate the diameter of the cervical opening. For instance, knuckle system 1 indicates a 1 cm diameter, knuckle system 2 indicates a 2 cm, and others in a similar fashion.

In addition to assessing cervical dilation, the operator also evaluates the position of the fetus by palpating the presenting part during the vaginal examination. This involves the following steps:

1. Identification of the presenting part: the operator uses their fingers to palpate and identify the presenting part of the fetus, which is typically the head in cephalic presentations or the buttocks in breech presentations. In a cephalic presentation, the operator may feel the hard, round contour of the fetal skull, whereas in a breech presentation, they may feel the soft, irregular shape of the fetal buttocks.

2. Assessing fetal position: the operator assesses the orientation of the fetal head or buttocks. For example, in a vertex presentation (head-first), the provider will feel whether the fetal head is flexed or extended. The flexion of the head will typically result in a round, smooth contour, while an extended head may feel more angular. In the case of a breech presentation, the position of the fetal buttocks and feet may help determine whether it is a frank breech (buttocks first) or a footling breech (feet presenting).

3. Fetal engagement: the provider can also assess whether the presenting part is engaged in the pelvis. Engagement refers to the part of the fetus descending into the birth canal. For example, in a vertex presentation, the provider may feel the fetal head descend further into the pelvic inlet.

4. Assessing fetal rotation: the operator may gently rotate their finger inside the vagina to assess any possible rotation of the fetus. This is especially important in cases where the fetal position is not optimal, such as when the baby is in a posterior position (head facing the mother’s back), which may lead to a longer or more complicated labor.

5. Assessing position relative to the pelvis: the healthcare provider can determine the fetal position in relation to the maternal pelvis using cardinal movements, such as flexion, descent, and internal rotation.

Once the fetal position is determined, the operator can record whether the baby is in a normal (anterior) or abnormal (posterior, transverse) position, which may affect the progress of labor and delivery.

Intrapartum ultrasound

Intrapartum ultrasound was performed using the Myriad Mindray color portable ultrasound M7 equipment with a convex array probe operating at a frequency of 3–5 Hz. When vaginal examination indicated cervical dilation of 5 cm, pregnant women in the study group were instructed to empty their bladder and assume a truncated position. The perineum was disinfected, and a disposable probe cover was placed on the probe. The probe was then positioned below the pubic symphysis and between the labia minora during the intervals between contractions to obtain a median sagittal section. This section clearly displayed the lower edge of the pubic symphysis and the lowest point of the fetal head. Measurements were taken and recorded. Ultrasound measurements were synchronized with vaginal examinations, performed between contractions, and lasted no longer than 5 min. Ultrasound examinations were initiated at the onset of labor and conducted every 2 h during the latent phase and every hour during the active phase until complete cervical dilation.

Each ultrasound examination involved two repeated measurements, and the final results were averaged. The ultrasound examinations were conducted by a clinician with three months of specialized training, while the vaginal examinations were performed by a midwife with over three years of experience. The examiners’ roles were fixed, and the two individuals did not communicate the results of each examination to maintain blinding.

Outcomes

Delivery outcomes

Delivery outcomes were recorded, including the mode of delivery, whether it was a painless delivery, whether an intermediate cesarean section was performed, and whether postpartum hemorrhage, episiotomy, perineal laceration, or fever occurred during delivery.

Ultrasound indices

Ultrasound measurements included fetal orientation, anterior and posterior cervical lip distance, fetal head position, Angle of Progression (AOP), and Head–Perineum Distance (HPD).

Neonatal condition

The basic conditions of the newborns were recorded, including newborn weight, Apgar score at 1 min, umbilical cord pH, presence of intrauterine distress, neonatal asphyxia, and other relevant indicators.

Statistical analysis

Statistical analysis was conducted using R statistical software (version 2.13.2). Measurement data were presented as mean ± standard deviation (mean ± SD), and the t-test was employed to analyze differences between the two study groups. Rank and dichotomous data were expressed as percentages (%), and the chi-square test was used to assess differences between the two study groups. The Kappa value was calculated to measure the level of agreement between the data obtained from vaginal examination and ultrasound outcomes during delivery. All statistical tests were two-sided, and a significance level of P < 0.05 was considered statistically significant.

Results

Baseline characteristics

Table 1 presents the general information of the subjects in both the control and study groups. In the control group, the mean maternal age was (30.25 ± 6.36) years, gestational week was (39.25 ± 1.05) weeks, and maternal BMI was (27.22 ± 4.06) kg/m2. In the study group, the mean maternal age was (32.11 ± 7.21) years, gestational week was (40.11 ± 1.26) weeks, and maternal BMI was (26.03 ± 4.10) kg/m2. There were no significant differences observed in the comparison of general data between the two groups (all P > 0.05).

Table 1.

Comparison of maternal baseline data

Characteristic	Control group	Study group	t	P
n
Maternal age ($\overline{x}$ ± s, years)	30.25 ± 6.36	32.11 ± 7.21
Gestational age ($\overline{x}$ ± s, weeks)	39.25 ± 1.05	40.11 ± 1.26
BMI ($\overline{x}$ ± s, kg/m2)	27.22 ± 4.06	26.03 ± 4.10

Consistency analysis of fetal head orientation determined by vaginal finger examination and ultrasound during labor and delivery

In the study group, the fetal head position was assessed using both vaginal finger examination and ultrasonography prior to manual rotation of the fetus. The results showed that vaginal finger examination identified occipital anterior position in 60 cases, occipital posterior position in 28 cases, and occipital transverse position in 12 cases. On the other hand, ultrasound examination at delivery identified occipital anterior position in 54 cases, occipital posterior position in 24 cases, and occipital transverse position in 22 cases. The Kappa values for agreement between the fetal head positions determined by ultrasound and the vaginal finger examination were 54.5% for occipital anterior position, 46.1% for occipital posterior position, 31.4% for occipital transverse position, and an overall agreement of 46.5% (Table 2).

Table 2.

Consistency analysis of fetal head orientation determined by vaginal finger examination and ultrasound during labor and delivery

	Vaginal finger examination			Total
	Occipital anterior position	Occipital posterior position	Occipital transverse position
Ultrasound examination
Occipital anterior position	48	8	2	58
Occipital posterior position	5	16	4	25
Occipital transverse position	7	4	6	17
Total	60	28	12	100

Comparison of delivery methods

The comparison of delivery methods between the two groups is presented in Table 3. In the control group, there were 17 cases of cesarean section, 83 cases of vaginal delivery, including 42 cases of natural vaginal delivery, 24 cases of instrumental vaginal delivery, and 17 cases of episiotomy. In the study group, there were 12 cases of cesarean section, 88 cases of vaginal delivery, including 65 cases of natural vaginal delivery, 16 cases of instrumental vaginal delivery, and 7 cases of episiotomy.

Table 3.

Comparison of delivery methods

	Natural vaginal delivery	Instrumental vaginal delivery	Episiotomy	Cesarean section
Control group	42	24	17	17
Study group	65	16	7	12
χ2	10.63	2.000	4.735	1.008
P	0.001	0.157	0.030	0.315

There was no significant difference in the cesarean section rate between the two groups (P > 0.05). However, the rate of natural delivery in the study group was significantly higher than that in the control group, and the rate of episiotomy was significantly lower than that in the control group, with statistically significant differences observed (all P < 0.05).

Comparison of adverse maternal outcomes

The comparison of adverse maternal outcomes between the two groups is presented in Table 4. In the control group, there were 24 cases of perineal tears, 9 cases of postpartum hemorrhage, and 11 cases of puerperal infections. In the study group, there were 20 cases of perineal tears, 7 cases of postpartum hemorrhage, and 8 cases of puerperal infections. Statistical analysis revealed no significant difference in the comparison of adverse maternal outcomes between the two groups (all P > 0.05).

Table 4.

Comparison of adverse maternal outcomes

	Perineal tear	Postpartum hemorrhage	Puerperal infection
Control group	24	9	11
Study group	20	7	8
χ2	0.466	0.272	0.532
P	0.495	0.602	0.469

Comparison of adverse neonatal outcomes

The comparison of adverse neonatal outcomes between the two groups of mothers is presented in Table 5. In the control group, there were 12 cases of neonates with a 1-min Apgar score < 7, 11 cases of umbilical cord pH < 7.2, 5 cases of mild asphyxia in neonates, and 3 cases of intrauterine distress. In the study group, there were 9 cases of neonates with a 1 min Apgar score < 7, 7 cases of umbilical cord pH < 7.2, 2 cases of mild asphyxia in neonates, and 4 cases of intrauterine distress.

Table 5.

Comparison of adverse neonatal outcomes

	1-min Apgar score < 7	Umbilical cord pH < 7.2	Mild asphyxia in neonates	Intrauterine distress
Control group	12	11	5	3
Study group	9	7	2	4
χ2	0.479	0.977	1.332	0.148
P	0.489	0.323	0.248	0.700

Statistical analysis revealed no significant difference in the incidence of adverse neonatal outcomes between the two groups (all P > 0.05).

Comparison of ultrasound indicators for different labor outcomes

The analysis of ultrasound indicators for different delivery outcomes was conducted in the study group, and the results are depicted in Fig. 1. Among the cases studied, there were 42 instances of spontaneous vaginal delivery with an occiput position angle (AOP) of (140.11 ± 19.01)˚ and head–perineum distance (HPD) of (3.92 ± 0.66) cm. Additionally, there were 24 cases of instrumental delivery with an AOP of (129.14 ± 17.11)˚ and HPD of (4.55 ± 0.71) cm. Furthermore, there were 17 cases of perineal incision with an AOP of (127.22 ± 12.22)˚ and HPD of (4.44 ± 0.82) cm. Lastly, there were 17 cesarean deliveries characterized by an AOP of (118.86 ± 8.94)˚ and HPD of (5.23 ± 0.91) cm.

Fig. 1.

Comparison of ultrasound indicators for different labor outcomes

Significant differences were observed in the AOP values among the different modes of delivery. Spontaneous vaginal deliveries exhibited a significantly higher AOP compared to other delivery modes, while cesarean deliveries demonstrated a significantly lower AOP than other delivery modes. Moreover, there were significant differences in HPD values among the different delivery modes. Spontaneous vaginal deliveries had a significantly lower HPD compared to other delivery modes, while cesarean deliveries showed a significantly higher HPD than other delivery modes. These differences were statistically significant (all P < 0.05).

Furthermore, the HPD of natural vaginal delivery was significantly lower than that of other delivery modes, and the HPD of cesarean delivery was significantly higher than that of other delivery modes, demonstrating a statistically significant difference (all P < 0.05).

Discussion

The process of labor and delivery is intricate, and it necessitates a thorough analysis of fetal position and other factors to ensure maternal safety. The initial stage of labor involves the dilation and effacement of the cervix, as well as the descent of the fetal head through the birth canal. The assessment of fetal head position is crucial in determining the progress and direction of labor, as well as the need for interventions like cesarean section [10].

Traditionally, healthcare providers have relied on vaginal examinations to assess the position of the fetal head. Vaginal palpation involves the direct manual palpation and examination of the mother’s vagina and cervix, allowing for the observation and assessment of fetal position, descent, and cervical dilation [11]. However, vaginal examinations are subjective assessments that depend on the experience and tactile sensitivity of the healthcare provider, and they may introduce errors and lack the accuracy of ultrasound imaging [12]. Diagnostic ultrasound, on the other hand, is a non-invasive examination method that enables the visualization and assessment of fetal position and maternal–fetal conditions without causing discomfort or pain to the mother [13]. During labor, ultrasound can provide more precise images and data, allowing for the visualization of fetal position, size, and presentation, as well as a comprehensive assessment of maternal and fetal well-being [14].

This study examined the concordance between occipital anterior, occipital posterior, and occipital transverse positions determined by ultrasound and vaginal examinations. The Kappa values for concordance were 54.5%, 46.1%, and 31.4%, respectively, resulting in an overall concordance rate of 46.5%. Vaginal examinations and intrapartum ultrasound are commonly utilized methods to assess the progress of labor. Vaginal examinations involve a subjective evaluation of cervical dilation, fetal descent, and the position and consistency of the cervix. In contrast, intrapartum ultrasound provides objective measurements of cervical length, fetal head position, and presentation. Additionally, it can identify abnormalities or complications during labor, such as fetal malposition or abnormal presentation [15]. Accurate assessment of fetal head position is crucial for appropriate labor management and choice of delivery methods. Incorrect fetal orientation can lead to improper placement of vacuum or forceps, increasing the risk of fetal injury and surgical failure. Persistent occipital retroversion, for example, is associated with a higher risk of surgical delivery and maternal and perinatal morbidity [16].

Traditionally, clinicians determine fetal head position by palpating the sagittal suture, anterior fontanelle, and posterior fontanelle. However, studies consistently demonstrate that palpation-based determination of head position is inaccurate when compared to ultrasound, with error rates ranging from 20 to 70%. In the present study, the agreement between intrapartum ultrasound and vaginal examinations in determining fetal orientation was poor, with both occipital posterior and occipital transverse positions showing less than 50% agreement, consistent with previous research [17]. Furthermore, the study observed a higher rate of transvaginal spontaneous delivery and a lower rate of episiotomy in the group where vaginal examinations were combined with intrapartum ultrasound compared to the group that relied solely on vaginal examinations. However, there was no significant difference in cesarean section rates between the two groups. The mode of delivery is influenced by various factors, including fetal and maternal status, labor progress, and obstetric judgment [22].

Some literature supports the role of intrapartum ultrasound in managing vaginal delivery. A retrospective study indicated that intrapartum ultrasound could help reduce unnecessary cesarean sections and episiotomies [18]. Additionally, a systematic evaluation found that the use of intrapartum ultrasound during fetal delivery reduced cesarean rates [19]. However, these findings remain somewhat controversial, and further studies are required to validate them. The combination of vaginal examinations and intrapartum ultrasound may have potential advantages in promoting spontaneous vaginal delivery and reducing episiotomy rates, although its effect on cesarean section rates has not been definitively determined [20, 21].

It is important to note that the mode of delivery is determined by multiple factors, and clinical judgment plays a significant role [22].

In this study, the researchers found significant differences in occiput position and head progression distance (HPD) among different modes of delivery. Natural vaginal delivery had a higher occiput position (AOP) compared to other modes, while cesarean delivery had a lower AOP. Conversely, natural vaginal delivery had a lower HPD compared to other modes, while cesarean delivery had a higher HPD. These ultrasound indicators during labor were closely associated with the mode of delivery [23]. Another study reported that when the HPD was not more than 40 mm, 93% of transvaginal deliveries occurred, with percentages decreasing to 67% for HPD between 40 and 50 mm, and 18% for HPD greater than 50 mm. For AOP, when it was ≥ 110°, 87% of deliveries happened through transvaginal delivery, while AOP between 100° and 110° had a transvaginal delivery rate of 82%, and AOP less than 100° had a transvaginal delivery rate of 38% [24]. Meta-analysis showed that in vaginal deliveries, the mean AOP values before and after 5 cm of cervical dilation were 100.9° and 125.3°, respectively. In surgically assisted deliveries, the mean AOP values before and after 5 cm of cervical dilation were 93° and 113.9°, respectively [25].

Conclusion

In conclusion, ultrasound during labor serves as an important adjunct tool in the vaginal trial of labor for primigravid women. It aids doctors in accurately determining the position of the fetal head, reducing the need for perineal incisions, and increasing the rate of natural vaginal delivery. Notably, the ultrasound findings differ significantly between women who undergo natural vaginal delivery and those with other delivery modes.

Author contributions

Chen Xu, Li Wei, and Li Hualin conceived the structure of the manuscript. Song Haibo, Fan Jianfeng, and Liu Mengting did the experiments and made the figures. Chen Zhen, Cao Ling, and Zhang Ge reviewed and edited the manuscript. All authors read and approved the final manuscript.

Funding

The authors have not disclosed any funding.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The authors declare that they have no competing interests.

Informed consent

All patients signed the informed consent form.