Prediction of Delivery Mode in Primiparous Women Based on Clinical and Intrapartum Ultrasound Parameters

doi:10.21203/rs.3.rs-4971706/v1

Objective: To monitor intrapartum ultrasound in primiparous women entering the first stage of labor and construct a model to predict the delivery mode for these women.

Materials and Methods: A total of 203 full-term singleton primiparous women admitted to our hospital for vaginal delivery between February 2022 to November 2023 were included. Initially, cervical dilation and fetal presentation were assessed by midwives through vaginal examination. Subsequently, ultrasound monitoring of the labor progress was conducted, with both assessments conducted blindly. Measurements were performed according to the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) guidelines, including abdominal assessment of fetal presentation and transperineal measurements of the angle of progression (AOP), head-perineum distance (HPD),progression distance (PD), and midline angle (MLA). Three measurements were performed for each parameter, and the average values were calculated. The participants were divided into a vaginal delivery group (163 cases) and a cesarean section group (40 cases) based on the delivery outcome. Clinical and ultrasound parameters were analyzed to determine differences between the two groups. Multiple logistic regression analysis was conducted to identify the independent influencing factors, and a nomogram was constructed. The robustness of the model was assessed and its clinical effectiveness was evaluated,which was then externally validated.

Results: (1) Maternal height, weight, gestational age, estimated fetal weight (EFW), maternal gestational diabetes, and maternal preeclampsia showed no statistical differences (P > 0.05), whereas epidural analgesia, fetal presentation, AOP, MLA, HPD, and PD exhibited significant differences (P < 0.05). (2) Multiple logistic regression analysis revealed that epidural analgesia, fetal presentation, AOP, and HPD were independent factors influencing vaginal delivery. The constructed nomogram exhibited a sensitivity of 74.2%, a specificity of 77.5%, and an area under the curve (AUC) of 0.808 (95% confidence interval: 0.729-0.886). (3) The nomogram prediction model was externally validated,and the constructed nomogram exhibited a sensitivity of 78.3%, a specificity of 80.0%, and an area under the curve (AUC) of 0.839 (95% confidence interval: 0.717-0.961).

Conclusion: Epidural analgesia, fetal presentation, AOP, and HPD were identified as independent factors influencing vaginal delivery in primiparous women. The nomogram model based on clinical and intrapartum ultrasound parameters demonstrated robustness and effectiveness, providing a valuable tool for predicting delivery mode.

First stage of labor

Intrapartum ultrasound

Primiparous women

Nomogram

Childbirth is the process of delivering a fetus from the mother's body and involves a complex physiological process. The main methods of delivery are vaginal delivery and cesarean section. Vaginal delivery has lower risks, a shorter duration of pain, facilitates early postpartum exercise, accelerates uterine recovery, and reduces the occurrence of complications such as neonatal respiratory distress syndrome. Cesarean section is an effective solution when complications arise during labor, ensuring rapid delivery and improved outcomes. However, this increases the risk of maternal hemorrhage and infection, leading to complications such as uterine adhesions, wound liquefaction, and intestinal adhesions postoperatively.

Spong CY et al.^[1]have indicated that the incidence of complications in vaginal delivery is significantly lower than that in cesarean section. The perinatal maternal and infant complications of low forceps delivery are not significantly.As living standards improve, the number of elderly mothers^[2] and obese mothers^[3] increases, resulting in a higher fetal weight^[4]. Additionally, interventions such as epidural anesthesia are becoming more common in obstetrics, leading to changes in the natural process of childbirth^[5]. Therefore, timely and accurate monitoring of labor progress and effective management are crucial for improving maternal and neonatal outcomes and promoting safe delivery^[6].

Currently, there is no objective method for quantifying the likelihood of successful vaginal delivery. Vaginal examination remains the primary clinical method for assessing labor progress.Researchs have found that the accuracy of vaginal examination is less accurate^[7];and it has limitations, including subjectivity and reliance on the examiner's experience. Moreover, it is an invasive procedure that can cause discomfort in pregnant women and increase the risk of intrauterine infection with repeated examinations^[8].

In contrast, ultrasound examination is a non-invasive, simple, and intuitive method with good repeatability. It is well accepted by pregnant women and directly reflects fetal presentation, fetal descent, cervical dilation, and the presence of a prolapsed cord. This helps to avoid an increase in the number of vaginal examinations and reduces the risk of intrauterine infection^[9]. The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) guidelines emphasize the objectivity, accuracy, and repeatability of intrapartum ultrasound in assessing fetal head position, presentation, and predicting the progress of labor, compared with clinical palpation,and it can also predict the outcome of vaginal delivery to some extent^[8].

Over the years, ultrasound has been increasingly utilized for labor monitoring, evolving from abdominal ultrasound for antenatal monitoring in the 1980s to intrapartum ultrasound detection. In 2002, Akmals et al.^[10]first applied intrapartum ultrasound to monitor fetal position; in 2006, Eggebø et al. ^[11]proposed a new ultrasound measurement parameter: the head-perineum distance (HPD), which reflects the shortest distance from the fetal head to the perineum. This parameter does not take into account the curvature of the birth canal, and the larger the value, the higher the level of the presenting part of the fetus is indirectly indicated. In 2009, Barbera^[12] proposed the angle of progression (AOP), which made up for the shortcomings of the HPD and is consistent with the characteristics of the curved birth canal. The larger the value, the lower the level of the presenting part of the fetus is indicated. Subsequently, researchers have proposed multiple ultrasound indicators reflecting the descent, rotation, and flexion of the fetal head, such as head direction (HD) ^[13], head-symphysis distance (HSD)^[14], progression distance (PD) ^[15], midline angle (MLA) ^[16], and occiput-spine angle (OSA) ^[17].However, research has shown that AOP and HPD are the most commonly used ultrasound indicators for assessing the degree of descent of the presenting part of the fetus, and they have good accuracy and repeatability. From 2010 to 2015, multiple scholars from abroad have studied intrapartum ultrasound and found that it can accurately determine fetal position, with a higher accuracy rate than clinical palpation ^[18^,^19]; in 2017, a study from abroad using transvaginal three-dimensional ultrasound to measure the progression angle, head direction, midline angle, and descent distance of the fetal head showed that the progression angle and descent distance have the best repeatability^[20^,^21] .

However, the weightings of these parameters in predicting the delivery mode for primiparous women during the first stage of labor remain unclear, and reliable predictive models are lacking. This study aims to address these gaps in the literature.

1. Study Participants

This prospective, observational study included 203 primiparous women who satisfied the inclusion criteria and were admitted to our hospital for vaginal delivery betweenFebruary 2022 to November 2023. The inclusion criteria were as follows: (1) primiparous women, (2) full-term pregnancies (37+ to 41+6 weeks), (3) in labor and entering the first stage of labor, (4) singleton pregnancies with cephalic presentation, (5) confirmation of cervical dilation by vaginal examination, and (6) absence of serious maternal-fetal diseases. Exclusion criteria were: (1) multiparous women, (2) twin or multiple pregnancies, (3) post-term pregnancies (gestational age ≥ 42 weeks), (4) preterm births (gestational age < 37 weeks), (5) non-cephalic presentation, (6) fetal congenital structural or chromosomal abnormalities, (7) uterine scar, (8) history of mid-term induction, (9) significant maternal-fetal diseases, (10) refusal of vaginal trial or refusal to undergo transperineal ultrasound examination, and (11) no surgical indications during the trial of labor, voluntary request for cesarean section, or fetal intrauterine distress during labor. A flowchart of the participant selection process is shown in Figure 1.

2. Equipment and Methods

Ultrasound measurements were performed using a Voluson S8 ultrasound machine (GE Medical Systems) equipped with a C1~5H convex probe. Measurements were taken during uterine contractions at intervals of at least 30 minutes to avoid interference with contractions.

(1) Assessment of Clinical Parameters:

Clinical parameters included maternal age, height, weight, gestational age, estimated fetal weight (EFW), maternal gestational diabetes, and maternal preeclampsia.

(2) Assessment of Fetal Presentation and Cervical Dilation:

Cervical dilation and fetal presentation were initially assessed by experienced midwives through vaginal examination. The fetal head station was determined according to the distance between the fetal head and the ischial spine. The participants were divided into vaginal delivery and cesarean section groups based on delivery outcomes.

(3) Intrapartum Ultrasound Parameters:

Ultrasound monitoring of the labor progress was conducted blindly by an experienced obstetrician who was not involved in the clinical management of labor. The ISUOG guidelines were followed for all the measurements. The following parameters were measured.

Fetal Presentation (abdominal assessment): The fetal head position was assessed using abdominal ultrasound, including whether the fetal head was in a flexed or extended position.Fetal position judgment as shown in Figure2.

Head-Perineum Distance (HPD): The distance between the fetal head and perineum measured along the axis of the birth canal.The measurement of HPD is shown in the figure4.

Progression Distance (PD): The distance traveled by the fetal head during contraction measured from the initial assessment to the subsequent assessment during contraction.The measurement of PD is shown in the figure5.

Midline Angle (MLA):The angle formed by the midline of the fetal skull and the line connecting the pubic symphysis and the center of the fetal head.The measurement of MLA is shown in the figure6.

Three measurements were performed for each parameter, and the average values were calculated for analysis.

3. Statistical Analysis

Statistical analyses were performed using SPSS version 26.0 (IBM Corp., Armonk, NY, USA) and R software version 4.1.1. Measurement data were expressed as mean ± standard deviation, and enumeration data were expressed as frequencies and percentages. The t-test or Mann-Whitney U test was used for measurement data, and the chi-square test or Fisher's exact test was used for enumeration data. Multiple logistic regression analysis was used to identify the independent influencing factors, and a nomogram was constructed based on the results. A receiver operating characteristic (ROC) curve was used to evaluate the predictive value of the model, and the area under the curve (AUC) was calculated. P < 0.05 was considered statistically significant.Bootstrap method was used for repeated sampling 1000 times for external validation of the nomogram prediction model. The odds ratio (OR) and 95% confidence interval (CI) were calculated for each variable.

1. Baseline Characteristics

A total of 203 primiparous women were included in the study, with 163 in the vaginal delivery group and 40 in the cesarean section group. The baseline characteristics of the study participants are listed in Table 1.

Table 1: Baseline characteristics of participants

	cesarean section （n=40）	vaginal delivery （n=163）	X²/t/z	P
age（year）	29(27,32)	28(26,31)	-1.620	0.105
height	159.5(156,162)	160(157,163)	-1.435	0.151
weight	65(58.5,73.5)	67(62,74)	-1.107	0.268
BMI（kg/m²）	26.81±4.57	26.67±3.38	0.172	0.864
Gestational weeks（weeks）	39.71(39.21,40.5)	39.86(39.14,40.43)	-0.149	0.882
diabetes（%）			0.02	0.887
no	33(82.50)	136(83.44)
yes	7(17.50)	27(16.56)
hypertension（%）			0.000	1.000
no	39(97.50)	157(96.32)
yes	1(2.50)	6(3.68)
hypothyroidism（%）			0.21	0.647
no	35(87.50)	149(91.41)
yes	5(12.50)	14(8.59)
estimated fetal weigh(EFW)	3484.5(3220.5,3626.5)	3339(3157,3567)	-1.284	0.199
biparietal diameter(BPD)	9.40±0.37	9.41±0.33	-0.164	0.870
headcir cumferenceHC	33.19±1.27	33.12±0.92	0.407	0.685
epidural analgesia（%）			8.923	0.003
no	6(15.00)	5(3.07)
yes	34(85.00)	158(96.93)
fetal presentation（%）			8.705	0.013
OA	12(30.00)	89(54.60)
OP	10(25.00)	20(12.27)
OT	18(45.00)	54(33.13)
AOP（°）	124.35±14.67	140.00±15.36	-5.825	0.000
MLA（°）	81.80±44.76	64.91±41.98	2.251	0.025
HPD（mm）	40.68±9.14	33.20±7.80	5.246	0.000
PD（mm）	42.20±16.06	52.85±15.3	-3.906	0.000

Maternal age, height, weight, gestational age, estimated fetal weight (EFW), maternal gestational diabetes, and maternal preeclampsia were not statistically different between the two groups (P > 0.05). However, significant differences were observed in epidural analgesia, fetal presentation, AOP, MLA, HPD, and PD (P < 0.05).

2. Logistic Regression Analysis

Multiple logistic regression analysis was performed to identify the independent influencing factors for predicting the delivery mode in primiparous women. The results are listed in Table 2.

Table 2: Logistic regression analysis of influencing factors

	B	S.E.	Wald	P	OR	95%CI		VIF
	B	S.E.	Wald	P	OR	下限	上限	VIF
epidural analgesia	1.606	0.777	4.271	0.031	4.983	1.086	22.853	1.011
fetal presentation								2.002
OA					1.000
OP	-3.236	1.527	4.495	0.031	0.039	0.002	0.783
OT	-1.308	0.934	1.959	0.155	0.270	0.043	1.688
AOP	0.052	0.024	4.773	0.004	1.053	1.005	1.103	2.795
MLA	0.025	0.013	3.414	0.052	1.025	0.998	1.053	1.860
HPD	-0.067	0.034	3.969	0.027	0.935	0.875	0.999	2.299
PD	-0.006	0.020	0.097	0.312	0.994	0.956	1.033	2.308

The analysis revealed that epidural analgesia (odds ratio [OR], 6.762; 95% confidence interval [CI]: 1.196-38.217), fetal presentation (OR, 1.281; 95% CI: 0.047-2.427), AOP (OR, 1.071; 95% CI: 1.022-1.123), and HPD (OR, 0.928; 95% CI: 0.869-0.991) were independent factors influencing vaginal delivery.

3. Construction and Validation of the Nomogram

Based on the results of the logistic regression analysis, a nomogram was constructed to predict the probability of vaginal delivery in primiparous women (Figure 7).

To use the nomogram, the value for each variable was located on the corresponding axis, and a line was drawn upward to determine the number of points for each variable. The total points were calculated by summing the points for all variables and locating the total points on the "Total Points" axis. A downward line was drawn to determine the probability of vaginal delivery.

The internal validation of the nomogram prediction model was performed using the Bootstrap method with 1000 repetitions of sampling, and the calibration curve showed good consistency between the actual observations and the nomogram predictions, with an absolute error of 0.024, indicating a high calibration degree of the model, as seen in Figure 8.The nomogram exhibited good discrimination, with a sensitivity of 74.2%, a specificity of 77.5%, and an AUC of 0.808 (95% CI: 0.729-0.886) (Figure 9).

4.External validation of the model

Sixty-one primiparas from Anxi County Maternal and Child Health Hospital were randomly selected for external validation of the model.The baseline characteristics of the two study participants are listed in Table 3.

Table 3: Baseline characteristics of participants in both groups

	Internal data（n=203）	External data （n=61）	X²/t/z	P
age（year）	29(27,31)	27(25,31)	-1.69	0.091
weight（kg）	67(62,74)	66.7(62,71)	-0.679	0.497
Gestational weeks（weeks）	39.86(39.14,40.43)	39.57(38.86,40.14)	-1.887	0.059
estimated fetal weigh(EFW)	3347(3164,3587)	3350(3100,3600)	-0.281	0.779
AOP（°）	136.92±16.42	135.48±20.99	0.562	0.575
HPD（mm）	34.67±8.59	35.84±8.56	-0.928	0.354
Outcomes（%）			0.679	0.410
cesarean section	40(19.70)	15(24.59)
vaginal delivery	163(80.30)	46(75.41)
epidural analgesia（%）			0.241	0.623
no	11(5.42)	5(8.20)
yes	192(94.58)	56(91.80)
fetal presentation（%）			2.390	0.303
OA	101(49.75)	26(42.62)
OP	30(14.78)	14(22.95)
OT	72(35.47)	21(34.43)

The comparison of clinical data between the two groups showed no statistically significant differences in maternal age, weight, gestational week, estimated fetal weight (EFW), amniotic fluid volume (AOP), maternal-fetal distance (HPD), fetal position, and the use of epidural anesthesia for pain relief, among other factors (P > 0.05).

A bootstrap method was used to resample 1000 times for external validation of the nomogram prediction model.The calibration curve graph shows that there is good consistency between the actual observations and the predictions of the nomogram, with an absolute error of 0.033, indicating a high calibration degree of the model. See Figure 10. The nomogram exhibited good discrimination, with a sensitivity of 78.3%, a specificity of 80.0%, and an AUC of 0.839(95% CI: 0.717-0.961).(Figure 11)

Obese mothers, the formation of cysts during the descent of the fetal head, deformation of the fetal head, overlapping of sutures, or excessive presentation of the fetus are all factors that affect the accuracy of vaginal palpation. In particular, when the fetal presentation is abnormal, such as persistent occiput posterior, face presentation, persistent occiput transverse, or anterior non-inclination, the difficulty of examination increases and the accuracy decreases^[22]. An abnormal fetal presentation is an important factor affecting the mode of delivery, which may lead to weakened contractions, prolonged descent of the fetal head, dystocia, failed trial of labor, and an increased cesarean section rate^{[23, 24]}. Real-time ultrasound can clearly display the relationship between the fetal head and the bony structures in the pelvis, accurately reflecting the descent of the fetal head, significantly reducing the difficulty of the examination and improving accuracy. Poppwski et al.^[25] conducted a study on the outcomes of real-time ultrasound monitoring, suggesting that monitoring low-risk mothers during labor may increase the cesarean section rate. Therefore, only by scientifically and reasonably applying real-time ultrasound and using it correctly can its maximum benefits be realized. Choi et al.^[26] conducted a prospective cohort study on the prediction of vaginal delivery outcomes using real-time ultrasound during labor, finding that the proportion of primiparas who underwent cesarean delivery due to occiput posterior in the first stage of labor was 37.5% (21/56), four and a half times the cesarean section rate for non-occiput posterior presentations [8.5% (9/106)]. Our study found that the cesarean section rate for occiput posterior was 33.3% (10/30), 25% (18/72) for occiput transverse, and 11.9% (12/101) for occiput anterior, consistent with Choi's research results. Therefore, accurately identifying abnormal fetal presentations in the first stage of labor, adjusting the mother's position in a timely manner, is conducive to correcting abnormal positions to normal, and also helps timely artificial position correction, which can reduce cesarean sections due to abnormal fetal positions, and is conducive to ensuring the safety of delivery. The results of our study also showed that AOP gradually increased with the progress of labor, while HPD gradually decreased, consistent with previous literature studies^{[27, 28]}.Therefore, these monitoring indicators have some value in guiding the mode of delivery. Currently, it is recommended to use real-time ultrasound in the following situations: prolonged first or second stage of labor or stalled labor; to clarify the position of the fetal head and the position of the presentation before vaginal surgical assistance; and to objectively assess abnormal presentation^{[29, 30]}.

Currently, there are few methods that can objectively predict the possibility of successful vaginal delivery. Eggebø et al.^[31] established a prediction model for vaginal delivery by calculating the risk scores of parameters such as AOP, HPD, fetal head circumference, fetal presentation, and cyst size, and in predicting complex surgical delivery, the area under the curve (AUC) of the six models ranged from 0.863 to 0.876, with the AUC of the binary regression model of AOP and HC being 0.876, and the calibration slope B being 0.98. Sainz et al.^[32] included AOP and HC in their study of simple regression models for predicting the possibility of vaginal assistance or failure, with the model's discriminative ability (AUC of 0.876) and calibration curve slope being 0.984. Rizzo et al.^[33] established a multivariate regression model for predicting the success rate of cephalic traction using maternal height, parity, prenatal ultrasound parameters (HC, EWF, and iliac bone angle), fetal presentation, and HPD, with the model's AUC being 0.913.

This study constructed a nomogram prediction model for delivery mode using parameters such as fetal presentation, epidural anesthesia, AOP, and HPD, with the model's C index being 0.808, reflecting a good potential clinical effect of the prediction model. The internal validation of the nomogram prediction model showed that there was good consistency between the actual observations and the nomogram predictions, with an absolute error of 0.024. Using the ROC curve to evaluate the value of the model in predicting the prognosis showed an AUC (95% CI) of 0.808 (0.729–0.886), indicating some predictive value for the mode of delivery. The external validation of the nomogram model showed that the actual observations and the nomogram predictions had good consistency, with an absolute error of 0.033, indicating a high calibration degree of the model. Using the ROC curve to evaluate the value of the model in predicting the prognosis showed an AUC (95% CI) of 0.839 (0.717–0.961), indicating some predictive value for the mode of delivery. When the optimal cut-off value was taken, the sensitivity and specificity were 78.3% and 80.0%, respectively, suggesting that the prediction model performed well. Therefore, the nomogram model constructed based on clinical and first stage of labor ultrasound indicators has robustness and effectiveness, and can be used for predicting the mode of delivery.

In summary, real-time ultrasound can judge the fetal presentation, position of the fetal head, and presentation of the fetus through some parameter indicators, which can be quantified. The prediction model constructed based on clinical and first stage of labor ultrasound indicators in this study can accurately assess the progress of labor; in cases of abnormal labor, it can provide some guidance for clinical decisions on cesarean section or vaginal delivery.

AUC：Area under curve

AOP：Angle of progression

BPD：Biparietal diameter

BMI:Models with a body mass index

EFW：Estimated fetal weight

HC：Head circumference

HPD：Head–perineum distance

ICC：Intraclass correlation coefficient

OP：Occipito-posterior

OA：Occipito-anterior

OT：Occipito-transverse

PD：Progression distance

ROC：Receiver operating characteristic cur

Acknowledgments

We express our gratitude to the participants who contributed to this study. We also appreciate the dedication of the midwives and obstetricians involved in the intrapartum ultrasound assessments.

Funding

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Author Contributions

Y C conceived the study, carried out the first draft of the manuscript. G L helped critically revise the manuscript for important intellectual content, were the mentors who designed and guided the research study. Y Z Provided externally validated data.W L ,Q G and Z C carried out the data analysis. C H and YC cared for patients and collected the clinical data. All authors contributed to manuscript revision, read, and approved the final submitted version of the manuscript.

Corresponding Author

Correspondence to Guorong Lyu

Ethical Approval

The study was conducted in accordance with the ISUOG Practice guidelines：Intrapartum ultrasound, and the protocol was approved by the Ethics Committee of

Quanzhou Maternity and Children's Hospital [Approval No. (2022) (16)].Informed consent was obtained from all the participants.The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation in this study was provided by the participants' legal guardians/next of kin.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Data availability statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

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No competing interests reported.

Prediction of Delivery Mode in Primiparous Women Based on Clinical and Intrapartum Ultrasound Parameters

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Abstract

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Materials and Methods

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Version 1