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\begin{document}

\title{Simple models to predict vaginal delivery and spontaneous fetal occiput
rotation based on intrapartum ultrasound and maternal characteristics}



\author[1]{Cheng Chen}%
\author[2]{Xiaoxing Zhang}%
\author[1]{Xiaohan Guo}%
\author[1]{Hangkai Bao}%
\author[2]{Peiying Luo}%
\author[2]{Huaqin Yang}%
\author[3]{Yali Wang}%
\author[1]{Yimin Zhou}%
\author[1]{Xiaofu Yang}%
\author[1]{Xia Ying}%
\author[2]{baihui zhao}%
\author[1]{Qiong Luo}%
\affil[1]{Womens Hospital, Zhejiang University School of Medicine}%
\affil[2]{Zhejiang University}%
\affil[3]{Changxing Maternity and Child Health Care Hospital}%


\vspace{-1em}



  
  \date{May 08, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Objective: To develop the prediction models for identifying fetal
occiput rotation and vaginal delivery based on intrapartum sonographic
findings. Design: Prospective observational study. Setting: Hangzhou,
China. Population: Nulliparous women with a singleton cephalic
presentation at term. Methods: Serial intrapartum ultrasonography were
performed in the latent phase (T1) and every three hours after that (T2,
T3 and T4). The managing clinicians performed paired digital vaginal
examinations to assess labor progress. Main Outcome Measures: Delivery
mode and successful internal fetal head rotation to the occiput anterior
(OA) position. Results: 614 women were included, of whom 524 underwent
vaginal delivery, and 90 required cesarean section. The percentage of
women with fetuses in non-occiput anterior position at the latent phase
was 53.9\% (331 cases), as 257 women underwent spontaneous rotation to
OA position before delivery, 74 were with persistent occiput posterior
or transverse position. We developed a model on the basis of the
maternal height and middle angel to predict the spontaneous fetal
occiput rotation, with the area under the receiver operating
characteristic curve (AUC) was 0.667 (95\%CI 0.583-0.751). Moreover, a
prediction model based on the maternal height and angle of progression
to evaluate whether women underwent vaginal delivery was also developed,
of which the AUC was 0.738(95\% CI: 0.763-0.793). Both models showed
satisfactory calibration. Conclusion: Simple models based on maternal
characteristics and intrapartum ultrasound findings might provide useful
information for predicting vaginal delivery and internal fetal occiput
rotation.%
\end{abstract}%



\sloppy


\textbf{Title:}Simple models to predict vaginal delivery and spontaneous
fetal occiput rotation based on intrapartum ultrasound and maternal
characteristics

\textbf{Authors}

Cheng Chen*\textsuperscript{,1}, Xiaoxin Zhang+\textsuperscript{,1},
Xiaohan Guo*, Hangkai Bao++, Peiying Luo+, Huaqin Yang+, Yali Wang\selectlanguage{ngerman}§,
Yimin Zhou\selectlanguage{english}++, Xiaofu Yang*, Xia Ying*, Baihui Zhao*, Qiong Luo*

\textbf{Affiliations}

*Department of Obstetrics, Women's Hospital, Zhejiang University School
of Medicine, Hangzhou, China

\selectlanguage{english}+Zhejiang University School of Medicine, Hangzhou, China

\selectlanguage{english}++Department of Ultrasound, Women's Hospital, Zhejiang University School
of Medicine, Hangzhou, China

SSChangxing Maternity and Child Health Care Hospital, Huzhou, China

Authors contributed equally to this study.

\textbf{Correspondence to:}

Pro Q. Luo, Department of Obstetrics, Women's Hospital, Zhejiang
University School of Medicine, Hangzhou, 310006, China; (E-mail:
luoq@zju.edu.cn)

Dr. B. Zhao Department of Obstetrics, Women's Hospital, Zhejiang
University School of Medicine, Hangzhou, 310006, China (E-mail:
zhaobh@zju.edu.cn)

\textbf{Running title:} Delivery prediction models, intrapartum
ultrasound

\textbf{ABSTRACT}

\textbf{Objective:}To develop the prediction models for identifying
fetal occiput rotation and vaginal delivery based on intrapartum
sonographic findings.

\textbf{Design:} Prospective observational study.

\textbf{Setting:} Hangzhou, China.

\textbf{Population:} Nulliparous women with a singleton cephalic
presentation at term.

\textbf{Methods:} Serial intrapartum ultrasonography were performed in
the latent phase (T1) and every three hours after that (T2, T3 and T4).
The managing clinicians performed paired digital vaginal examinations to
assess labor progress.

\textbf{Main Outcome Measures:} Delivery mode and successful internal
fetal head rotation to the occiput anterior (OA) position.

\textbf{Results:} 614 women were included, of whom 524 underwent vaginal
delivery, and 90 required cesarean section. The percentage of women with
fetuses in non-occiput anterior position at the latent phase was 53.9\%
(331 cases), as 257 women underwent spontaneous rotation to OA position
before delivery, 74 were with persistent occiput posterior or transverse
position. We developed a model on the basis of the maternal height and
middle angel to predict the spontaneous fetal occiput rotation, with the
area under the receiver operating characteristic curve (AUC) was 0.667
(95\%CI 0.583-0.751). Moreover, a prediction model based on the maternal
height and angle of progression to evaluate whether women underwent
vaginal delivery was also developed, of which the AUC was 0.738(95\% CI:
0.763-0.793). Both models showed satisfactory calibration.

\textbf{Conclusion:} Simple models based on maternal characteristics and
intrapartum ultrasound findings might provide useful information for
predicting vaginal delivery and internal fetal occiput rotation.

\selectlanguage{english}\textbf{Key words:} Prediction model, intrapartum ultrasound, angle of
progression, midline angle, vaginal delivery, fetal occiput rotation

\textbf{Tweetable abstract}

Simple models based on maternal height and ultrasound findings can
predict the delivery mode and internal fetal head rotation.

\textbf{INTRODUCTION}

Operative deliveries are associated with increased maternal (obstetric
hemorrhage, perineal injuries, wound infection) \textsuperscript{1,
2}and neonatal morbidity (neonatal seizures, and intracranial
hemorrhage)\textsuperscript{2-6}. It is important to monitor labor
progress to prevent these maternal and neonatal complications
\textsuperscript{7}. The conventional assessment currently relies on a
serial digital examination, which has been demonstrated to be
subjective, imprecise, and poorly reproducible \textsuperscript{8, 9}.
Furthermore, digital vaginal examinations can also cause discomfort
\textsuperscript{10} and may introduce infection \textsuperscript{9}.
Intrapartum ultrasonographic examinations have been introduced to
complement assessments of labor progress \textsuperscript{11}.

Occiput posterior (OP) and occiput transverse (OT) positions account for
15 to 49\% at the onset of labor \textsuperscript{12-15}, and in most
cases, the fetal head will rotate spontaneously to the occiput anterior
(OA) positions. Accumulating evidence implicates the persistent OP or OT
position is associated with obstetric complications, including prolonged
labor, operative delivery, postpartum hemorrhage and third or
fourth-degree perineal lacerations\textsuperscript{16-18}. The
spontaneous internal rotation of the fetal occiput from the transverse
or posterior position to the anterior position is associated with
multiparity, a maternal age of fewer than 35 years, maternal stature,
BMI, and newborn birth weight (\textless{}4000 g) \textsuperscript{14,
19, 20}. However, there is still no model, which can help predict
successful fetal head rotation during the delivery.

In the last decade, various sonographic parameters have been proposed,
including the angle of progression (AoP)\textsuperscript{21},
head-perineum distance (HPD)\textsuperscript{22} and midline angle (MLA)
\textsuperscript{23}. Several studies have reported that intrapartum
ultrasonography is a reliable and noninvasive approach for determining
fetal head position, station and descent \textsuperscript{24-27}. The
AoP has been used to assess fetal head station and be predictive of
spontaneous vaginal delivery or successful instrumental vaginal
delivery\textsuperscript{28-31}, and the MLA was associated with the
fetal head station and rotation\textsuperscript{11}.

In the majority of studies, a single assessment of sonographic
parameters was performed in either the first or second labor
phase\textsuperscript{30, 32-35}. Moreover, few studies have developed
predictive models associated with successful internal rotation and
vaginal delivery. Therefore, the primary aim of the present study was to
assess serial intrapartum ultrasound measurements at different time
points during delivery for the prediction of the delivery mode in
nulliparous women. A secondary aim was to develop a model to predict
successful internal fetal occiput rotation.

\textbf{METHODS}

This prospective, longitudinal observational, single-center study was
conducted in the Women's Hospital at Zhejiang University School of
Medicine in Hangzhou, China, between May 2020 and November 2020.
Nulliparous women with a singleton pregnancy in a cephalic presentation
at term (37 or more full weeks of gestation) attempting vaginal birth
were eligible for the study. Women were excluded if they were under 18
years of age, had intrauterine death or had emergencies (e.g., premature
placental abruption, uterine rupture, cardiac disease of New York Heart
Association (NYHA) grade 3 or 4, eclampsia). We also excluded the cases
if they required cesarean deliveries purely because of fetal distress.
The study was approved by the local ethics and research committees
(IRB-20200148-R). Written consent was obtained from the women who agreed
to participate.

\textbf{Ultrasound assessments}

The ultrasound assessments were carried out by four operators (X.X.Z.,
H. K. B., P.Y.L. and H.Q.Y.), who have had at least three year's
obstetric ultrasound experience and were not involved in the clinical
management of the recruited women. When the participants were in the
semirecumbent position with an empty bladder, a two-dimensional
transperineal ultrasonography scan was performed to assess the AoP, MLA
and HPD using a GE Logiq V2 ultrasound system (GE Healthcare, USA) with
a 2-5 MHz curvilinear transducer, as previously
described\textsuperscript{21-23}. The fetal occiput position was
assessed transabdominally or transperineally \textsuperscript{36}, and
the position was defined using the 12-hour clock system (see
SUS1)\textsuperscript{37}. The AoP is the angle between the long axis of
the pubic bone and the leading part of the fetal skull in the
midsagittal plane \textsuperscript{21} (Figure 1a). The HPD is the
shortest distance between the outer bony limit of the fetal skull and
the perineum in the transverse plane \textsuperscript{22}(Figure 1b).
The MLA is defined as the angle between the anteroposterior axis of the
maternal pelvis and the midline of the fetal head
\textsuperscript{23}(Figure 1c).

Digital examinations were performed by experienced obstetricians or
midwives to assess cervical dilation, fetal head position and fetal head
station before the ultrasonographic scans. The fetal head station was
defined as the distance from the lowest part of the fetal head to the
ischial spine (i.e., from -3 to +3, with 0 at the ischial spine). The
interval between the paired examinations was no more than ten minutes,
and the researchers were blinded to the findings of both examinations.
The first intrapartum ultrasonographic examination was performed during
the first stage of labor when the cervix was fully effaced and dilated
by at least 3-4 cm but no more than 6 cm (latent phase) (T1), and
intrapartum ultrasonographic scans were performed every three hours
after that (T2, T3 and T4) until delivery.

The clinical team followed the standard local protocol of the research
unit to manage labor progress. With a fully effaced cervix and cervical
dilation of at least 3 cm, the women in labor were admitted to the
predelivery room for continuous fetal heart monitoring. Labor
augmentation with oxytocin was considered if there was suboptimal
uterine power and unsatisfactory progress, as demonstrated by a
partogram, and there was no evidence of obstructed labor. Failure to
progress was defined as longer than 12 hours in the latent phase or
cervix failed to dilate at a rate of 1cm per hour for at least 2 hours.

Maternal clinical data, such as age, gestational age at delivery,
height, body mass index (BMI), induced or spontaneous labor, premature
rupture of the membrane, the use of epidural anesthesia, labor
augmentation with oxytocin, the final mode of delivery and the
indication for operative delivery, were recorded. Data on the neonatal
outcomes were also collected: sex, birth weight, Apgar scores after 1
and 5 minutes and the admission of the newborn to the neonatal unit.
Gestational age was determined by the date of the first day of the last
menstrual period and confirmed by the first-trimester ultrasound
measurement of crown-rump length\textsuperscript{38}. BMI was calculated
according to the standard formula, and overweight was defined as BMI \selectlanguage{english}[?]
25 kg/m\textsuperscript{2}. Successful internal rotation was defined as
the fetal head rotating to the occiput anterior (OA) position from a
non-occiput anterior (non-OA) position (transverse or posterior) during
the labor. Vaginal delivery in our unit included spontaneous and
operative delivery using forceps.

\textbf{Calculation of sample size}

We assumed that the non-OA (OP and OT) prevalence during the first stage
of labor was 60\%. We hypothesized that the rate of spontaneous internal
rotation to the OA position would be 80\% in the group, and the
proportions of cesarean delivery in the non-OA position and OA position
were 30\% and 10\%, respectively. The total estimated sample size was
507 by accepting an alpha risk of 0.05 (two-sided) and a power of 80\%.
Finally, we increased the number by 20\% (634 women) to compensate for
the dropout rate and any secondary exclusion.

\textbf{Statistical analysis}

Descriptive statistics were calculated, and the data are presented as
the means (standard deviations {[}SDs{]}) or medians (ranges) for
numeric variables. Comparisons of normally and nonnormally distributed
continuous variables between study groups were performed using the
Kruskal-Wallis test. Categorical variables are reported as numbers
(percentages) and were compared by Fisher's exact test. Multivariable
logistic regression analyses were performed to control potential
cofounders and predict the successful fetal head rotation and vaginal
delivery. The variables chosen in these logistic models were significant
or marginally significant (P\textless{}0.1) in univariate analysis and
were described in the previous studies \textsuperscript{20, 39}.
Discrimination (the ability of the model to differentiate between the
presence and absence of the event) was assessed by the area under the
receiver operating characteristic curve (AUC). While calibration was
assessed with calibration plots to measure how well the predicted
outcome of the model agrees with the observed outcome. Statistical
results with two-sided P values were reported, and a value of P
\textless{} 0.05 was considered statistically significant. Statistical
analyses were performed using Statistical Package for Social Sciences
(SPSS) version 26 (IBM, Armonk, NY, USA) and R statistical software,
version 4.0.3.

\textbf{RESULTS}

\textbf{Maternal characteristics}

A total of 634 nulliparous women were recruited, fifteen of whom were
excluded because of incomplete data, and five withdrew due to discomfort
during the ultrasound examination. Of the remaining 614 women, 524
(85.3\%) women underwent vaginal delivery and 90 (14.7\%) were required
cesarean delivery. The percentage of women with fetuses in non-OA
position at the first time of ultrasound examination was 53.9\% (331
cases) in our study, as 159 (25.9\%) cases were in the OP position and
172 (28.0\%) were OT position. The main characteristics of the
participants are shown in Table 1.

\textbf{Comparison of clinical findings and ultrasound parameters by the
mode of delivery}

The maternal and neonatal demographic characteristics compared between
the vaginal delivery and cesarean delivery groups are shown in Table S1.
There were no significant differences between these two groups, except
for maternal height (161.2 +- 4.6 vs. 158.8+-5.1 cm, P \textless{} 0.001)
and neonatal birth weight (3390.5 +- 366.7 vs. 3550.7 +- 380.4 g, P
\textless{} 0.001) (Table S1). Focusing on the sonographic parameters,
the women who underwent vaginal delivery had a significantly larger AoP
compared with the women who required cesarean section over time (Table
2). For HPD measurements, the cesarean delivery group showed
significantly longer distance than did the vaginal delivery group (Table
2). Accounting for MLA, the vaginal delivery group showed comparable
measurements to the cesarean delivery group initially (T1: 55.27+-27.36
vs. 60.09+-27.93deg; P = 0.201), whereas from three hours afterward, a
significantly narrower angle was observed among the women who achieved
vaginal delivery (T2: 47.42 +- 27.36 vs. 68.18+-25.49deg, P\textless{}0.001;
T3: 38.96 +- 24.37 vs. 63.18 +- 30.79deg; P=0.004) (Table 2).

\textbf{A simple model to predict the internal rotation}

A total of 257(77.6\%) women with a fetus in non-OA position during the
latent phase underwent spontaneous rotation to OA position before
delivery; however, 74 (22.4\%) were persistent OP or OT position.
According to the occurrence of internal fetal head rotation, the
individual characteristics were similar besides maternal height
(161.0+-4.4 vs. 159.7+-5.2 cm; P = 0.022) (Table S2). The multivariable
logistic regression analysis demonstrated that the MLA (adjusted odds
ratio {[}aOR{]}: 1.021, 95\% confidence interval {[}CI{]}:1.008-1.034)
and maternal height (aOR: 1.107, 95\% CI:1.026-1.195) were the
significant predictors of spontaneous fetal occiput rotation after
adjusting for maternal age, gestational age, overweight, premature
rupture of the membrane, labor induction, oxytocin augmentation and the
use of epidural analgesia (Table S3). The final model that predicted
internal fetal head rotation based on MLA at the first ultrasound scan
and the maternal height was shown in Table 3, which obtained the AUC was
0.667 (95\% CI, 0.583-0.751; P\textless{}0.001) (Figure 2). The
calibration curve shows good agreement between predicted and observed
probabilities for the occurrence of spontaneous fetal head rotation
(Figure 3(a)).

\textbf{A simple model to predict vaginal deliveries}

We performed a forward multivariate logistic regression analysis model
that included the factors associated with the delivery mode in the
univariate analysis (P\textless{}0.1). In this model, the AoP and
maternal height were the independent factors associated with the mode of
delivery after adjustment for confounders, including maternal age,
gestational age, overweight (BMI\selectlanguage{english}[?]25 Kg/m\textsuperscript{2}), premature
rupture of the membrane, labor induction and oxytocin augmentation
(Table S4). The combination of maternal height and the AoP could
evaluate whether women were to undergo vaginal delivery, yielding an AUC
of 0.738 (95\% CI, 0.763-0.793; P\textless{}0.001) at T1, 0.820 (95\%
CI, 0.752-0.888; P\textless{}0.001) at T2 and 0.940 (95\% CI,
0.885-0.995; P\textless{}0.001) at T3 (Figure 4), respectively. Figure
3(b) showed the optimal calibration of the prediction model. This model
was also suitable for women with fetuses in the occiput posterior or
transverse position at the latent phase, yielding AUC 0.725 (95\% CI,
0.649-0.801; P\textless{}0.001) at T1 and 0.790 (95\% CI, 0.705-0.874;
P\textless{}0.001) at T2, respectively (Figure S2).

\textbf{DISCUSSION}

\textbf{Main Findings}

In the present study, we performed intrapartum ultrasonographic
assessments of fetal head station and position, which differed
significantly at various times during the labor. We developed a binary
logistic regression model based on maternal height and angle of
progression to predict 73.8\% of vaginal deliveries at the latent labor
phase. Moreover, a simple prediction model combining middle angel and
maternal height for estimating the spontaneous fetal head rotation was
also obtained. Because these two models both require only two parameters
(one clinical variable and one intrapartum ultrasound parameter) that
can be easily acquired, we suppose both models can be applied in any
delivery unit.

\textbf{Strengths and Limitations}

The strengths of our study include the following: (1) this study is a
prospective longitudinal study that measured ultrasound parameters of
the fetal head station and position throughout the first and second
labor stages in women with singleton pregnancies at term. (2) In this
double-blinded study, the researchers and the managing clinicians were
both blinded to the respective findings to avoid potential bias. (3) New
objective and simple models based on the ultrasound parameters and
clinical variables were shown to predict the internal fetal head
rotation and delivery mode. However, we do acknowledge some limitations.
Firstly, our study population included only Chinese women, and our
results might not be representative of other ethnic populations.
Secondly, neonatal birth weight is also a significant risk factor
according to the mode of delivery in our observational study; however,
we did not introduce this item as a predictive factor because of lacking
a precise method to estimate the fetal weight before delivery.
Furthermore, we should carry out the external validation of the
prediction model.

\textbf{Interpretation (in light of other evidence)}

Non-occiput anterior (transverse or posterior) positions are associated
with a high risk of cesarean section, operative vaginal delivery and
other peripartum complications, including third- or fourth-degree
perineal lacerations, postpartum hemorrhage and
chorioamnionitis\textsuperscript{13, 18, 40, 41}. Compared with neonates
born in the OA position, neonates born in a non-occiput anterior
position have a lower Apgar score, a higher risk of neonatal intensive
care unit admissions and higher rates of birth trauma
\textsuperscript{18, 19}. The incidence of persistent OP position is
between 5\% and 12\% \textsuperscript{12, 18, 42}, and that of
persistent OT position varies from 3\% to 8\%\textsuperscript{13, 40,
43}. A study by Petitjean et al. \textsuperscript{44} identified
oxytocin augmentation, excessive gestational weight gain, direct OP
position and macrosomia as independent factors associated with non-OA to
OA rotation during the first stage of labor. In our study, maternal
height is the single individual factor associated with internal fetal
occiput rotation. On the other hand, the degree of fetal head rotation,
as measured by the MLA, was parallel between vaginal and cesarean
delivery groups at first. However, the MLA of the women who experienced
vaginal delivery was narrower subsequently, indicating the occurrence of
spontaneous rotation.

Moreover, we develop a simple model based on the intrapartum sonographic
parameter and maternal characteristic to predict spontaneous fetal head
rotation in the first stage of labor. We think this finding might
provide the clinicians an opportunity to take earlier action to reduce
the obstetric complications associated with persistent OP and OT
positions.

Accumulating studies showed that maternal and neonatal characteristics,
including parity, maternal age, height, BMI, neonatal birth weight and
fetal head position, are independent factors that affect the mode of
delivery \textsuperscript{28, 45, 46}. Burke et al.
\textsuperscript{47}reported a risk prediction model for cesarean
delivery using five parameters (maternal age, height, BMI, fetal head
circumference and fetal abdominal circumference), with excellent
discrimination (Kolmogorov- Smirnov, D statistic, 0.29; 95\% CI, 0.28-
0.30). Furthermore, Eggebo et al. \textsuperscript{39}introduced
intrapartum ultrasound to developed another risk score based on maternal
characteristics (gestational age, maternal weight, BMI and cervical
dilatation), occiput position and intrapartum findings (head perineal
distance and caput succedaneum) to predict vaginal birth, which yielded
an AUC of 0.853 (95\%CI, 0.678-1.000). Our study illustrated a much
simple prediction model based on only two parameters (maternal stature
and AoP) for evaluating the delivery mode in the nulliparas in the first
stage of labor. We started the intrapartum ultrasound assessment during
the latent phase (cervical dilatation less than 6 cm), which allowed
clinicians to identify early the women who required cesarean delivery.
We caution that the knowledge derived from our model should not alter
obstetric decision making. However, our study might provide useful
information about the chance of spontaneous rotation and vaginal birth,
allowing appropriate interventions at the proper time.

\textbf{CONCLUSION}

In conclusion, our study provides simple models based on maternal
characteristics and intrapartum ultrasound findings that can predict the
chance of vaginal birth and successful internal fetal head rotation in
nulliparous women. We suppose these models can be implemented in any
delivery unit.

\textbf{Disclosure of Interests}

The authors report no conflict of interest. Completed disclosure of
interest forms are available to view online as supporting information.

\textbf{Contribution to Authorship}

Concept and design: CC, XXZ, XHG, BHZ and QL.

Data acquisition: HKB, YMZ, HQY, PYL and YLW.

Statistical analysis: CC, XXZ, XFY and XY

Drafting of manuscript: CC, BHZ and QL.

Review of manuscript: all authors.

\textbf{Details of Ethics Approval}

Ethical approval for the study was obtained from the Ethics Committee of
Women's Hospital, Zhejiang University School of Medicine on 25 May 2020
(Number IRB-20200148-R).

\textbf{Funding:}

The study was supported by Nature Science Foundation of Zhejiang
Province (Grants: LY20H040009), and State Key Foundation of Zhejiang
Province (Grants: WKJ-ZJ-2126).

\textbf{Acknowledgment}

We thank all the women and physicians who participated in this study.

\textbf{Legends}

Figure 1. Sonographic parameters of fetal head descent and rotation: (a)
The angle of progression (AoP) in the transperineal longitudinal plane;
(b) The head-perineum distance (HPD) measured on a sagittal scan and (c)
the midline angle in the transperineal axial plane.

Figure 2. Receiver operating characteristic curve for the prediction
model of the midline angle combined with the maternal height. The area
under the curve (AUC) for the prediction of successful fetal head
rotation was 0.667 (95\% CI, 0.583-0.751; P\textless{}0.001).

Figure 3. Calibration curves for prediction models. (a) Model of fetal
occiput rotation; (b) Model of vaginal delivery.

Figure 4. Receiver operating characteristic curve of the combination of
maternal height and angle of progression (AoP) for predicting vaginal
delivery at different scan intervals. The first scan time (T1) was at
the latent labor phase (red line). Subsequent scans were performed at 3
hours intervals (T2, blue line; T3, green line). The areas under the
curves (AUCs) for the prediction model were 0.738 (95\% CI, 0.763-0.793;
P\textless{}0.001) at T1, 0.820 (95\% CI, 0.752-0.888;
P\textless{}0.001) at T2 and 0.940 (95\% CI, 0.885-0.995;
P\textless{}0.001) at T3, respectively.

Table 1 Maternal and newborn characteristics of participants

Table 2 The angle of progression (AoP), head--perineum distance (HPD)
and midline angle (MLA) at different time points, according to the mode
of delivery

Table 3 Final logistic regression models to predict spontaneous fetal
occiput rotation and vaginal delivery

\textbf{Supporting information}

The following supplementary materials are available for this article:

Figure S1. Classification of fetal occiput position based on 12-hour
clock face.

Figure S2. Receiver operating characteristic curve of the model for
predicting vaginal delivery in nulliparous women with fetuses in the
occiput posterior or transverse position at latent phase.

Table S1. Maternal and neonatal characteristics of the study population,
according to the mode of delivery.

Table S2. Maternal and neonatal characteristics of the study population,
according to internal rotation.

Table S3. Maternal and neonatal characteristics of the study population,
according to internal rotation.

Table S4. Logistic regression analysis for the prediction of delivery
mode, according to serial ultrasound evaluations

\textbf{References}

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Table 1 Maternal and newborn characteristics of participants\selectlanguage{english}
\begin{longtable}[]{@{}lll@{}}
\toprule
Variables & Variables & Findings\tabularnewline
\midrule
\endhead
Maternal age, y, mean\selectlanguage{ngerman}±SD & Maternal age, y, mean\selectlanguage{ngerman}±SD &
29.0\selectlanguage{ngerman}±3.2\tabularnewline
\selectlanguage{english}[?]35, n (\%) & [?]35, n (\%) & 33(5.4\%)\tabularnewline
Maternal height, cm, mean\selectlanguage{ngerman}±SD & Maternal height, cm, mean\selectlanguage{ngerman}±SD &
160.8\selectlanguage{ngerman}±4.8\tabularnewline
Maternal weight, kg, mean±SD & Maternal weight, kg, mean\selectlanguage{ngerman}±SD &
67.5\selectlanguage{ngerman}±8.6\tabularnewline
Body mass index, kg/m\textsuperscript{2}, mean ±SD & Body mass index,
kg/m\textsuperscript{2}, mean \selectlanguage{ngerman}±SD & 26.1\selectlanguage{ngerman}±2.9\tabularnewline
Overweight, n (\%) & Overweight, n (\%) & 382(62.2\%)\tabularnewline
Gestational age at delivery, weeks, mean\selectlanguage{ngerman}±SD & Gestational age at
delivery, weeks, mean\selectlanguage{ngerman}±SD & 39.6\selectlanguage{ngerman}±1.0\tabularnewline
Gestational pathology, n (\%) & Gestational diabetes mellitus, n (\%) &
93(15.1\%)\tabularnewline
& Gestational hypertensive disorder, n (\%) & 34(5.5\%)\tabularnewline
& Intrahepatic cholestasis of pregnancy, n (\%) &
13(2.1\%)\tabularnewline
Fetal head position at inclusion & Occiput anterior, n (\%) &
283(46.1\%)\tabularnewline
& Occiput transverse, n (\%) & 172(28.0\%)\tabularnewline
& Occiput posterior, n (\%) & 159(25.9\%)\tabularnewline
Premature rupture of membranes, n (\%) & Premature rupture of membranes,
n (\%) & 155(25.2\%)\tabularnewline
Epidural, n (\%) & Epidural, n (\%) & 557(90.7\%)\tabularnewline
Induction of labor, n (\%) & Induction of labor, n (\%) &
234(38.1\%)\tabularnewline
Augmentation, n (\%) & Augmentation, n (\%) & 411(66.9\%)\tabularnewline
Delivery mode & Vaginal delivery, n (\%) & 524(85.3\%)\tabularnewline
& Cesarean delivery, n (\%) & 90(14.7\%)\tabularnewline
Birth weight, g, mean \selectlanguage{ngerman}± SD & Birth weight, g, mean \selectlanguage{ngerman}± SD &
3414.0\selectlanguage{ngerman}±372.8\tabularnewline
Newborn gender, male, n (\%) & Newborn gender, male, n (\%) &
326(53.1\%)\tabularnewline
Apgar 1 min, median (range) & Apgar 1 min, median (range) &
10(3-10)\tabularnewline
Apgar 5 min, median (range) & Apgar 5 min, median (range) &
10(5-10)\tabularnewline
Meconium amniotic fluid, n (\%) & Meconium amniotic fluid, n (\%) &
98(16.0\%)\tabularnewline
NICU, n (\%) & NICU, n (\%) & 58(9.4\%)\tabularnewline
\bottomrule
\end{longtable}

Overweight: Body mass index [?]25 kg/m\textsuperscript{2}; NICU, Admission
to neonatal intensive care unit.

Table 2 The angle of progression (AoP), head--perineum distance (HPD)
and midline angle (MLA) at different time points, according to the mode
of delivery\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
HPD (cm) & P value & \textbf{\textless{}0.001} &
\textbf{\textless{}0.001} & \textbf{0.003} & \textbf{-}\tabularnewline
\midrule
\endhead
& Cesarean delivery & \selectlanguage{ngerman}\vtop{\hbox{\strut 5.16±0.89}\hbox{\strut (n=90)}}
& \selectlanguage{ngerman}\vtop{\hbox{\strut 5.02±1.01}\hbox{\strut (n=40)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 4.81±0.55}\hbox{\strut (n=10)}} & -\tabularnewline
& Vaginal delivery & \selectlanguage{ngerman}\vtop{\hbox{\strut 4.57±0.97}\hbox{\strut (n=524)}}
& \selectlanguage{ngerman}\vtop{\hbox{\strut 4.09±1.17}\hbox{\strut (n=268)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 3.69±1.15}\hbox{\strut (n=98)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 3.39±0.93}\hbox{\strut (n=16)}}\tabularnewline
MLA (°) & P value & 0.201 & \textbf{\textless{}0.001} & \textbf{0.004} &
\textbf{-}\tabularnewline
& Cesarean delivery &
\selectlanguage{ngerman}\vtop{\hbox{\strut 60.09±27.93}\hbox{\strut (n=86)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 68.18±25.49}\hbox{\strut (n=40)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 63.18±30.79}\hbox{\strut (n=10)}} & -\tabularnewline
& Vaginal delivery &
\selectlanguage{ngerman}\vtop{\hbox{\strut 55.27±27.36}\hbox{\strut (n=518)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 47.42±27.36}\hbox{\strut (n=268)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 38.96±24.37}\hbox{\strut (n=98)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 35.47±21.60}\hbox{\strut (n=16)}}\tabularnewline
AoP\selectlanguage{english}(deg\selectlanguage{english}) & P value & \textbf{\textless{}0.001} &
\textbf{\textless{}0.001} & \textbf{\textless{}0.001} &
\textbf{-}\tabularnewline
& Cesarean delivery & 105.32\selectlanguage{ngerman}±12.76(n=90) &
\selectlanguage{ngerman}\vtop{\hbox{\strut 110.46±12.5}\hbox{\strut (n=40)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 111.35±11.1}\hbox{\strut (n=10)}} &\tabularnewline
& Vaginal delivery &
\selectlanguage{ngerman}\vtop{\hbox{\strut 116.06±16.96}\hbox{\strut (n=524)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 128.43±22.93}\hbox{\strut (n=268)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 138.78±22.43}\hbox{\strut (n=98)}} &
\selectlanguage{ngerman}\vtop{\hbox{\strut 143.97±45.00}\hbox{\strut (n=16)}}\tabularnewline
& Time point & T1 & T2 & T3 & T4\tabularnewline
\bottomrule
\end{longtable}

Table 3 Final logistic regression models to predict spontaneous fetal
occiput rotation and vaginal delivery\selectlanguage{english}
\begin{longtable}[]{@{}llll@{}}
\toprule
Variables in the equation & aOR & 95\% CI & \emph{P}
value\tabularnewline
\midrule
\endhead
spontaneous rotation model & spontaneous rotation model & spontaneous
rotation model & spontaneous rotation model\tabularnewline
Midline angle & 1.019 & 1.007-1.031 & \textbf{0.002}\tabularnewline
Maternal height & 1.083 & 1.010-1.162 & \textbf{0.026}\tabularnewline
Constant & -12.634 & &\tabularnewline
Delivery model & Delivery model & Delivery model & Delivery
model\tabularnewline
Angle of progression & 1.052 & 1.034-1.071 &
\textbf{\textless{}0.001}\tabularnewline
Maternal height & 1.134 & 1.075-1.195 &
\textbf{\textless{}0.001}\tabularnewline
Constant & -23.944 & &\tabularnewline
\bottomrule
\end{longtable}

aOR, adjusted odds ratio; CI, confidence interval.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Firgure1/Firgure1}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/ROC-rotation/ROC-rotation}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/calibration/calibration}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/ROC-delivery/ROC-delivery}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/12-hour/12-hour}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/ROC-NOOA-delivery/ROC-NOOA-delivery}

\end{center}
\end{figure}

\selectlanguage{english}
\FloatBarrier
\end{document}

