Analysis of spontaneous labor progression of breech presentation at term.

BACKGROUND: Cervical dilatation curves are widely used to describe normal and abnormal labor progression for cephalic presentation. Labor curves for breech presentations have never been described.
OBJECTIVES: The aims of this study were to examine the pattern of labor progression in women with a breech presentation and to determine whether the type of breech or parity can influence the speed of cervical dilatation. STUDY
DESIGN: We analyzed the labor data from 349 women with a term, singleton, and breech fetus after spontaneous onset of labor in 2010-2018. Cesarean deliveries were excluded. The patterns of labor progression were described by examining the relationship between the elapsed times from the full dilatation and cervical dilatation stages. Average labor curves were developed using repeated-measures analysis with 3rd degree polynomial modeling. The results were interpreted according to parity and the type of breech.
RESULTS: The first stage of labor progression was divided into a latency phase from 0 to 5 cm of dilatation and an active phase from 5 to 10 cm. In the active phase, the median speed of cervical dilatation was 1.67 cm/h [1.25, 2.61] (2 cm/h for multipara and 1.54 cm/h for nullipara). The difference by parity was significant in the active phase (p< 0.05). The cervical dilatation rate from 3 cm to 10 cm did not significantly differ between the complete and frank breeches (1.56 cm/h vs 1.75 cm/h, p = 0.48). However, the median cervical dilatation rate from 8 cm to complete dilatation was faster for complete breeches (1.92 cm/h versus 1.33 cm/h, p = 0.045).
CONCLUSION: As with cephalic presentation, the first stage of labor progression for breech presentation can be divided into a latent and active phase. Labor progression should be interpreted with respect to parity, and women should be informed that the type of breech does not seem to influence the cervical dilatation rate when there is adequate management.

Introduction

Cervical dilatation curves are widely used to describe normal and abnormal labor progression. Referential data from the Consortium on Safe Labor for spontaneous deliveries are used for the management of labor progression to optimize recourses for obstetric interventions, such as the use of oxytocin and cesarean section [1, 2]. These data serve as a reference to define normal values for the first stage of labor progression, which can be divided into a latent phase and an active phase, which does not start until at least 5–6 cm of dilatation is observed [1]. Friedman was the first to report mean labor curves by dividing the labor process into several stages and phases [3, 4]. Because of the methodological limitations of these preliminary studies, Zhang et al. reported contemporary curves developed with repeated-measures regression and polynomial function. In this retrospective study, the 95th percentile rate of active phase dilatation for a vertex presentation varied from 0.5 cm/h to 0.7 cm/h for nulliparous women and from 0.5 cm/h to 1.3 cm/h for multiparous women.

However, these previous studies excluded nonvertex presentation, and no labor curves have been established for breech presentation at term. Because there is insufficient data in the literature, it is not possible to recommend specific labor durations for breech delivery. Moreover, it is difficult to conclude whether recommendations concerning oxytocin use for labor arrest described for cephalic presentation are also applicable for breech labor management [5]. Contemporary data about cervical dilatation in this specific situation may be useful for reducing cesarean deliveries for these pregnancies.

The first objective of this study was to describe the progression of labor with breech presentation and the spontaneous onset of labor. The secondary objectives were to determine whether parity and type of breech (frank or complete) can influence the cervical dilatation speed.

Materials and methods

We conducted a single-center retrospective cohort study of consecutive term breech deliveries from 1 January 2010 to 31 December 2018 at a single academic teaching hospital. Under French regulations, the study was exempt from institutional ethics review because it was a retrospective observational study using anonymized data from medical records. The women were systematically informed that the obstetrical and neonatal data could be used for the evaluation of medical practices and were explicitly informed that they could sign an opposition form.

Women were eligible after 37 weeks of gestation with a live breech presentation, spontaneous onset of labor and a vaginal delivery. We excluded cesarean deliveries and home births. During the study period, an attempt of vaginal breech delivery at term was attempted if the following hospital-specific guidelines were met: normal findings for low-dose CT pelvimetry in nulliparous women (anteroposterior inlet diameter ≥ 105 mm, transverse diameter ≥ 115 mm, bispinous diameter ≥ 95 mm and a Magnin Index ≥ 23), a clinical adequate maternal pelvis for multiparous women, no fetal head deflexion, and no suspected fetal macrosomia.

Concerning labor management, epidural analgesia was recommended, and oxytocin augmentation without labor induction was allowed to induce regular uterine contractions, if needed. The latency phase was a period characterized by painful uterine contractions and variable changes in the cervix with some degree of effacement and slow progress of dilatation up to 5 cm. The active phase of labor was a period characterized by regular painful uterine contractions, a significant degree of cervical effacement and dilatation up to 5 cm. The management protocol is available in the S1 Appendix.

Detailed demographic data were extracted from the patients’ records, including their medical and obstetrical history (maternal age, parity, body mass index). We collected detailed labor and delivery information from the medical files and electronic partograms (ePartogram, DIAMM® software, version 8.7 Rev 14), including the cervical examination time, cervical dilatation (3 to 10 cm) and station at each examination, total duration of the first and second stages, duration of the expulsive efforts, use of oxytocin, type of anaesthesia, type of breech presentation (frank breech or incomplete breech and complete breech), birth injury perineum, episiotomy and total volume of bleeding. We included incomplete breech in the frank breech group. The following neonatal data were collected: the umbilical arterial pH, arterial lactates, the Apgar score at 5 minutes (min), the birthweight, the head circumference and whether the newborn was transferred to the intensive care unit.

We characterized the labor progression patterns by examining the relationship between the elapsed times from the full dilatation and cervical dilatation stages, as previously described by Zhang et al. [6, 7]. Because the participants were admitted at various cervical dilatation stages, we performed interval-censored regression analyses, with 10 cm of dilatation as the starting point, moving backward in time. We constructed average labor curves using repeated-measures analysis with 3rd degree polynomial modeling. A 3rd order polynomial had the best fit for our cervical dilatation data. We characterized the labor durations (min) by examining the distribution of time intervals from one cervical dilatation stage to the next and ultimately to full dilatation. The median, first quartile and third quartile of the cervical dilatation velocity were calculated.

The patients were divided into two groups according to parity: nulliparous and multiparous (> 1). For each group, the average duration of cervical dilatation has been collected. Thus, the median cervical dilatation rate to the full dilatation (cm/h) has been calculated. The cervical dilatation curves of the first stage of labor were created. The cervical dilatation curves were also described with respect to the type of breech presentation. The qualitative variables were compared using the chi-squared test. The normality of the quantitative variables was tested by the Kolmogorov-Smirnov test. In accordance with the results of this test, the statistical significance of the differences in the qualitative variables was tested using the paired Student t-test or paired Mann–Whitney U test. Pearson’s correlation coefficient (r2) between the mean values was calculated. Analyses were performed by R software (online at http://www.R-project.org, the R Foundation for Statistical Computing, Vienna, Austria). For the continuous data, the variables are presented as the mean value ± standard deviation (SD) or the median and interquartile range. The categorical variables are presented as frequencies and percentages. All reported p values are two-tailed. P values of less than 0.05 were regarded as statistically significant.

Results

Out of the 23,337 women who delivered at the hospital during the study period, 18 968 (96,46%) had cephalic presentations, and 650 (3,3%) had breech presentations. Two hundred forty-nine (38.3%) women had a cesarean breech delivery: 155 before labor and 94 during labor. Among the 495 attempts of vaginal breech delivery, 401 ultimately resulted in a vaginal delivery. Fifty-two breech deliveries were excluded. Finally, 349 patients were included in the study: 137 were primiparous, and 212 were multiparous. The most common type of breech presentation was complete in both the multiparous (n = 127) and nulliparous groups (n = 105) (Fig 1). The maternal and neonatal characteristics are summarized in the Table 1. Frank breech presentations were significantly more common in the primiparous patients (p = 0.002) (Table 1). Oxytocin was introduced in the latent phase for 39 patients (14.4%), in the active phase for 150 patients (55.5%) and finally during the 2nd stage for 81 patients (30%).

Fig 1

Flow chart.

Table 1

Baseline characteristics of the study population by parity.

	Multiparous (n = 212)	Nulliparous (n = 137)	p-test
Maternal age at delivery (years)	31.32 (4.93)	28.57 (4.15)	<0.001
Gestational age at delivery (weeks)	39.52 (1.16)	39.38 (1.10)	0.264
Prepregnant BMI (kg/m2)	22.96 (5.22)	22.28 (4.29)	0.201
Epidural analgesia (n, (%))	197 (92.9)	134 (97.8)	0.019
Oxytocin use (n, (%))	154 (72.6)	116 (84.7)	0.013
Type of breech presentation: (n, (%))
• Complete Breech    • Frank and incomplete breech	85 (40.1)	32 (23.4)	0.002
	127 (59.9)	105 (76.6)
Postpartum hemorrhage: (n, (%))			0.837
• hemorrhage > 500 ml and < 1L    • hemorrhage > 1L	8 (3.8)	7 (5.1)
	2 (0.9)	1 (0.7)
Birth injury perineum: (n, (%))			0.671
Absence of any lesion	45(52.9)	55 (57.3)
First degree	23 (27.1)	24 (25.0)
Second degree	12 (14.1)	14 (14.6)
Third degree	4 (4.7)	2 (2.1)
Fourth degree	1 (1.2)	0
Episiotomy (n, (%))	5 (2.4)	18 (13.1)	<0.001
Newborn birth weight (grams)	3135.28 (428.34)	3024.05 (402.24)	0.016
Newborn Head circumference (cm)	33.81 (4.92)	34.09 (3.23)	0.561
Newborn Apgar score at 5 minutes (mean (SD))	9.78 (0.70)	9.73 (0.77)	0.505
Umbilical arterial pH (mean (SD))	7.16 (0.11)	7.13 (0.13)	0.013
Arterial lactates (mean (SD))	5.22 (2.37)	6.54 (2.60)	<0.001
Newborn transfer: (n, (%))			0.563
• Neonatal unit    • Neonatal intensive care unit	4 (10.0)	3 (8.1)
	3 (7.5)	1 (2.7)

In the whole cohort, the first stage of labor could be divided into a latency phase from 0 to 5 cm of dilatation and an active phase from 5 to 10 cm of dilatation. The maximal slope in the rate of change in cervical dilatation over time did not start until at least 5 cm was observed (Fig 2). The cervical dilatation rate was slower than 1 cm/hour in the latency phase and faster than 1 cm/hour in the active phase (Table 2). The median velocity of cervical dilatation from 3 to 10 cm was 1.65 cm/h [1.27, 2.59]. In the active phase, from 5 to 10 cm, the median speed of cervical dilatation was 1.67 cm/h [1.25, 2.615] (Table 3).

Fig 2

Cervical dilatation curves of breech presentation with spontaneous labor and vaginal deliveries.

Table 2

Number of patients (n) analyzed and the median dilatation rate from one cervical dilatation stage to the next for primiparous and multiparous females.

Results are expressed as median (IQR).

Cervical Dilatation stage (cm)	Multiparous (n = 212)	Nulliparous (n = 137)	Median dilatation rate p-test	Number of patients p-test
3 to 4	0.83 [0.67, 1.00], n = 38	0.80 [0.65, 1.00], n = 35	0.337	0.337
4 to 5	0.86 [0.70, 1.00], n = 42	1.00 [0.81, 1.00], n = 34	0.125	0.125
5 to 6	1.00 [1.00, 1.00], n = 40	1.00 [0.67, 1.00], n = 32	0.074	0.074
6 to 7	1.00 [0.92, 1.00], n = 37	1.00 [0.75, 1.00], n = 25	0.222	0.222
7 to 8	1.00 [0.83, 1.00], n = 39	1.00 [0.80, 1.00], n = 21	0.703	0.703
8 to 9	1.00 [0.80, 1.00], n = 49	1.00 [0.86, 1.00], n = 33	0.956	0.956
9 to 10	1.00 [0.92, 2.00], n = 99	1.00 [0.86, 1.33], n = 63	0.167	0.167

Table 3

Median cervical dilatation rate to the full dilatation (cm/h) for overall and according to type of breech presentation and parity.

Results are expressed as median (IQR).

Cervical dilatation (cm)	Overall (n = 349)	Complete breech (n = 117)	Frank breech (n = 123)	p	Multiparous (n = 212)	Nulliparous (n = 137)	p
3 to 10	1.65 [1.27, 2.59] n = 179	1.56 [1.21, 2.57], n = 52	1.75 [1.29, 2.63], n = 127	0.482	1.73 [1.33, 2.73] n = 100	1.62 [1.17, 2.33] n = 79	0.256
4 to 10	1.80 [1.20, 2.67 n = 147	1.71 [1.20, 2.40], n = 50	2.00 [1.26, 2.67], n = 97	0.257	2.00 [1.27, 3.00] n = 87	1.48 [1.13, 2.22] n = 60	0.053
5 to 10	1.67 [1.25, 2.61] n = 183	2.00 [1.25, 3.10], n = 67	1.67 [1.18, 2.50], n = 116	0.316	2.00 [1.31, 3.08] n = 110	1.54 [1.11, 2.22] n = 73	0.045
6 to 10	1.60 [1.11, 2.78] n = 142	1.50 [1.23, 3.39], n = 54	1.75 [1.00, 2.38], n = 88	0.386	1.70 [1.13, 3.43] n = 80	1.50 [1.10, 2.00] n = 62	0.210
7 to 10	1.50 [1.00, 2.94] n = 138	1.50 [1.15, 2.40], n = 44	1.50 [1.00, 3.00], n = 94	0.716	1.50 [1.00, 2.40] n = 82	1.50 [1.00, 3.00] n = 56	0.622
8 to 10	1.39 [0.98, 2.67] n = 160	1.92 [1.00, 3.57], n = 52	1.33 [0.91, 2.22], n = 108	0.045	1.60 [1.00, 2.67] n = 99	1.33 [0.92, 2.03] n = 61	0.445
9 to 10	[0.86, 1.93] n = 162	1.05 [1.00, 2.96], n = 52	1.00 [0.86, 1.33], n = 110	0.017	1.00 [0.92, 2.00] n = 99	[0.86, 1.33] n = 63	0.167

The percentage of patients admitted at early stages of dilatation was higher in the primiparous women: 79 (57.7%) primiparas and 100 (47.2%) multiparas were admitted from 3 cm of cervical dilatation (Table 3). For each one-centimeter interval of cervical dilatation, there was no significant difference in the number of patients assessed between the two groups (Table 2). Cervical dilatation was faster in the multiparous women than in the primiparous women and accelerated as labor progressed in both groups (Fig 3). From 5 to 10 cm, the median cervical dilatation time was 202 min for the primiparas and 178 min for the multiparas (p = 0.12) (Table 4). The median speed of cervical dilatation in the active phase (5 to 10 cm) was 1.54 cm/h [1.11, 2.22] for the primiparas and 2.00 cm/h [1.31, 3.08] for the multiparas (p <0.05) (Table 3).

Fig 3

Cervical dilatation curves for the primiparous and multiparous women.

Table 4

Time (min) required from one cervical dilatation stage to the full dilatation.

Results are expressed as mean and standard deviation.

Cervical dilatation (cm)	Multiparous (Min)	Nulliparous (Min)	p-test
3 to 10	251,46 (129,30)	276,14 (141,28)	0,225
4 to 10	211,36 (126,25)	246,17 (122,86)	0,099
5 to 10	178,10 (105,97)	202,33 (100,13)	0,123
6 to 10	153,89 (97,24)	170,31 (89,01)	0,302
7 to 10	137,98 (89,55)	126,61 (76,67)	0,439
8 to 10	94,79 (69,47)	97,36 (61,83)	0,813
9 to 10	57,89 (38,72)	61,75 (34,15)	0,519

The rate of cervical dilatation from 3 cm to 10 cm was not significantly different between the complete and frank breech groups (1.56 cm/h vs 1.75 cm/h, p = 0.48) (Table 3). However, when the labor curves were juxtaposed in the active phase, and median cervical dilatation from 8 cm to complete dilatation was observed to be faster for complete breeches (1.92 cm/h versus 1.33 cm/h, p = 0.045) (Table 3, Fig 4).

Fig 4

Cervical dilatation curves according to the type of breech presentation.

Discussion

Principal findings

This study is the first to propose labor curves of breech presentation at term in spontaneous labor and highlights that the first stage of labor can also be divided into a latent and active phase. In the cohort in our study, the latent phase lasted until cervical dilatation reached 5 cm and gradually accelerated from 5 to 10 cm during the active phase. Cervical dilatation was faster at the beginning of the latency phase in the multiparas, and the start of the active phase was progressive for both groups. According to parity, we found that both the latency phase and the active phase were faster for the multiparous women. The difference by parity was significant in the active phase (p< 0.05) but no significant differences were found in the rate of cervical dilatation across the types of breech.

Clinical implications

The American College of Obstetricians and Gynecologists (ACOG) and the American Society of Maternal Fetal Medicine (SMFM) have proposed guidelines to manage cervical dilatation during labor for cephalic presentations. The active phase is defined to begin from 6 cm, and neither prolonged nor stopped labor should be diagnosed before 6 cm of dilatation. Cesareans should be performed in the absence of progression for 4 hours after the administration of oxytocin if the uterine activity is satisfactory and the membranes are ruptured or in the absence of progression for 6 hours after the administration of oxytocin if uterine activity is not satisfactory [2]. The absence of a consensual definition of labor progression during breech presentation and the lack of standard protocols can lead to unnecessary cesarean sections being performed. In 2006, only 18/30 maternities included in the PREMODA study were able to provide a protocol in which conditions for an attempt at breech vaginal delivery were detailed. The rate of vaginal deliveries ranged from 1.7 to 49.7%, depending on the center, and there was no threshold to define an abnormally long first stage of labor [8].

Results

In 1997, a study involving 266 patients with a breech presentation reported an average labor duration of 460 min [9]. In our study, the average cervical dilatation time from 5 to 10 cm was 202 min for the primiparas and 178 min (p = 0.1) for the multiparous, which were consistent with the results of the PREMODA study since the duration of the active phase was less than four hours for 66.2% of the women included. The use of oxytocin augmentation during spontaneous labor can explain this difference. Indeed, the rate of oxytocin augmentation was approximately 77% in our study and was similar to that of the PREMODA study (70%) (8). This high rate could reflect a lack of tolerance by the medical team toward a prolonged latent phase for breech delivery compared to cephalic presentation.

It is important to distinguish the total duration of labor and cervical dilatation speed during both the latent and active phases. According to the British guidelines for breech delivery, the first stage of labor should be managed with the same principles as with a cephalic presentation [10]. Oxytocin may be considered for a contraction frequency fewer than four in ten, and a cesarean section should be offered when the progress of labor is slow, regardless of parity. However, this decision should take into account that the cervical dilatation speed seems to spontaneously differ in breech delivery cases by the stage of first labor and parity.

It is interesting to compare the median duration of labor for cephalic presentation reported in the National Collaborative Perinatal Project and our data for breech presentation [11]. The median cervical dilatation time from 5 to 10 cm was 2.1 (h) for nulliparous patients with a cephalic presentation and was 3.36 h in our study. In the Zhang et al. study, the median velocity of cervical dilatation for the nulliparous patients was 1.2 cm/h at 5 cm and 2.8 cm/h at 8 cm [6]. Thus, the cervical dilatation rate in nulliparous women seems to be slower for breech presentations than for cephalic presentations, despite the high rate of oxytocin use in our study (77%). In our study oxytocin was introduced in the latent phase for 39 patients (14.4%), in the active phase for 150 patients (55.5%) and finally during the 2nd stage for 81 patients (30%). The use of oxytocin is described in the protocol. Only 14.4% of patients receive oxytocin in latent phase. But in view of the new recommendations and these first studies describing breech labor, a reflection on the use of oxytocin can be considered (5).

In our study, 3.15% of newborns were transferred, of which 2.00% (n = 7) were transferred to neonatology and 1.15% (n = 4) to intensive care unit. These rates are lower than reported in the French national perinatal survey in 2016 (4.2% in neonatology and 2,4% in intensive care units) (12). The arterial pH was significantly lower with an average of 7.13 in nulliparous versus 7.16 in multiparous (p = 0.013). Concerning the 4-newborn transferred to the intensive care unit, 3 had an arterial pH < 7 and one had an arterial pH of 7.20 but the Apgar score was > 7 at 5 min.

The cervical dilatation rate in the multiparous women remained faster than that in the nulliparous women throughout the entire labor period. These data should be taken into account before abnormal first-stage labor progression is diagnosed for breech presentation after the spontaneous onset of labor. Recently, a comparative study between frank and complete/incomplete breeches provided evidence that perinatal morbidity was not associated with the fetal leg posture in intended vaginal deliveries. There was no significant difference in the rate of cesarean section indicated for labor arrest between the frank and complete breech groups or in the duration of the first stage of labor [12]. The median velocity of cervical dilatation from 3 cm to 10 cm did not differ between the complete and frank breeches. Although complete breech presentation can be regarded as unfavorable for vaginal delivery, our results suggest that complete breech presentation can also be a good dilator pole for the cervix when pelvic accommodation is optimal. In the active phase, cervical dilatation was faster from 8 cm to full dilatation for complete breeches.

Research implications

In current practice, some exclusion criteria for a vaginal birth approach may be opinion based, and cesarean section is often offered for cases with complete breech because of a high risk of cord prolapse or poor cervical dilatation. When women expecting a breech baby undergo counseling, it is important to inform them that a frank or a complete breech does not significantly influence labor progression during the first stage of labor.

Limitations

There are some limitations that should be considered when interpreting our results. In this study, women who underwent a cesarean delivery were excluded such as the Zhang’s study, which can lead to selection bias (1). According to labor progression analyses reported in the current literature, cervical dilatation was slower in the studies that included patients who had a cesarean section. Since women undergoing cesarean section in the first stage are more likely to have a prolonged labor period, their exclusion likely shortened the total duration and duration for progression in one centimeter increments [2]. Moreover, some practices have changed over the ten years of this study, particularly concerning the administration of oxytocin during labor. In our study, the use of oxytocin probably had an impact on labor duration since the median duration was 4.6 h in the nulliparous women and was 6.9 h in the study by Zhang about the contemporary patterns of spontaneous labor [1]. Oxytocin for augmentation was used in nearly half of the women included in the Consortium on Safe Labor and 74.9% in the PREMODA Study (8). It is possible that the high rate of labor augmentation reported in our study suggests a more prophylactic than a therapeutic role. A reflection on the high-level use of oxytocin should be considered and discussed in specific recommendations about management of breech delivery.

Conclusions

Our results confirm that the first stage of labor for breech presentation can be divided into two phases: the latent phase, from 0 to 5 cm, and the active phase, from 5 to 10 cm. During attempts of vaginal breech delivery, labor progression should be assessed according the latent and the active phases, and according the parity. Women should be informed that the type of breech does not seem to significantly influence the cervical dilatation during spontaneous labor.

Protocol for attempted vaginal breech delivery.

(DOCX)

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Partograph.

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Characteristics.

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3 Mar 2021

PONE-D-20-40976

Analysis of spontaneous labor progression of breech presentation at term

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Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you for the opportunity of reviewing this very interesting paper. The authors aimed to describe the course of labor for breech delivery with comparison according the parity and the type of breech (frank or complete). The overall message is that the course of labor is similar that the one described for vertex presentation without significant impact of the type of breech. This results are very interesting and original. It should have a clinical impact by reducing the level of intervention for stagnation in case of breech delivery and might contribute to reduce the CS rate in this situation. I only have very few comments especially for discussion. You will find my detailed comments below

Detailed comments

Abstract

- Indicate I the abstract if the difference according parity is significant or not

Main text

- Line 93: remove date information which not appears adequate here

- How do the authors interpret the surprising difference between multiparous and nulliparous women with a higher speed of dilatation for nulliparous in the active phase?

- Does your population includes women with history of CS? Which proportion?

- Why not including cesarean section during labor for failure of progress for a secondary analysis (at least those at full cervical dilatation) and compare the dilatation curse between those who deliver vaginally and those with CS for failure of progress?

- I’d like a more important discussion about our management in labor ward. Indeed, it is widely reported that a breech delivery have to be a “fast and easy delivery”. Your results support the opposite and that finally the course of labor is not very different between a vertex or breech presentation. Discuss that your results suggest that we might consider reducing our level for intervention in case of breech delivery for stagnation of dilatation especially for this latency phase that must be respected. This might be moderate for the second stage of labor for whom a longer duration of this stage might be an alarm signal for dystocia and lead to consider CS.

- Provide a short and concise conclusion by the end of the conclusion

Reviewer #2: Thank you to give me to opportunity to review this work about labor progression of breech presentation at term. However, I remain perplex because it seems difficult to conclude about labor curves from a sample of 349 breech presentation in a single center. Moreover, lacking data (or not presented in the manuscript) did not allow us to draw conclusions and extrapolate the results.

I have some major concerns:

- The high rate of oxytocin use (77%) limits extrapolation of the results. Author should consider to stratify analyses with and without oxytocin use.

- How did the author define the onset of labor from their data ?

- The beginning of the active phase of labor is 3 cm in this paper. The author should change this threshold for 5 or 6 cm as demonstrated in Zhang’s publication

- I do not understand why the authors decided to exclude cesarean deliveries. Why did they not choose the censure of these data? It would be necessary to include all women reaching the second stage of labor

- Please describe the protocol of oxytocin use during labor in breech presentations in the center in the material section. Because this protocol is not provided, extrapolation of the data is questionable.

- Neonatal issues are also questionable. How explain the high rate of neonatal transfers: 17.5% in multiparous and 10.8% in nulliparous women. A description of transfer indications is lacking. Apgar score should be reported as percentages of newborn with 5 minutes Apgar score <7 in Table 1. Moreover, please provide information about arterial pH at birth (mean and rate <7.0, <7.10 …)

- In the results section, a description of labor management is lacking: cervical dilation at admission in labor ward unit, rate of amniotomy, cervical dilation when oxytocin was started … Without a such description of labor practices, extrapolation of these results remains questionable.

- Table 3, last line (from 9 to 10), the significance of the comparison between complete and franck breech is probably wrong: p=0.017 ???

- In the conclusion of abstract and the manuscript, please delete “when there is adequate management”. This subjective comment seems inappropriate considering the high rate of oxytocin use and the high rate of neonatal transfer.

About minor concerns:

- in the introduction section, please delete in lines 93-94 “12/30/2020 2:17:00 PM” and change the police in lines 102-108

- in the materials and methods section, please provide the ethic registration number

Reviewer #3: The authors performed this study in order to assess cervical dilatation length during the passive and active labor of women presenting with a fetus in breech position. The primary objective was to evaluate labor progression of primiparous and multiparous women in cases of breech presentation as labor curves in such cases are not available. The secondary outcome was to determine whether the type of breech or parity can influence the speed of cervical dilatation.

This a retrospective study, performed in a single French center between 2010 – 2018. The inclusion criteria were : women eligible after 37 weeks of gestation with a live breech presentation if the onset of labor was spontaneous and they completed the first and second stages with a vaginal delivery. The authors collected labor progression patterns by examining the relationship between the elapsed times from the full dilatation and cervical dilatation stages. The labor durations (min) was characterized by examining the distribution of time intervals from one cervical dilatation stage to the next and ultimately to full dilatation. The median, first quartile and third quartile of the cervical dilatation velocity were calculated.

During the study period 3.3 % of the presentation were breeches. A total of 495 (76.1%) of women with a breech presentation on 650 attempted a vaginal delivery. The authors illustrates the different velocities of cervical dilatation depending on parity, type of breeches and passive/active phase.

Overall, the clinical topic is interesting as labor curves in case of breech presentation has not been previously publish. The methodology of this study is sound. Furthermore, the discussion is well constructed and the authors address the limits of their study.

They are some minor revision points, which are the following:

General:

Proof-reading by native English speaker is mandatory, in order to improve its readability and correct several typos.

Introduction:

Line 93-94 : “12/30/2020 2:17:00 PM”.

Line 101 – 108 : the police is different than from the rest of the text.

Methods:

Line 140 : Why was the episiotomy and total volume of bleeding rate collected as it is not presented in the results ?

Table 1

Please precise if the numbers are median (IQR) or mean (SD).

Reviewer #4: Scientific merit

This is a unique study and is the first to attempt to create labour curves for spontaneous vaginal breech delivery at term. The authors must be highly commended for this very valuable and important piece of work. As someone who is a proponent of vaginal breech this is certainly a very interesting and novel approach that could be built on in the future.

However, given the single centre design, the seemingly aggressive use of syntocinon, which has not been explained, and the lack of complete outcome data, more work is needed before these curves could be used in other centres which may have rather more physiological approaches to childbirth.

Background

The authors have corrected identified a gap in our knowledge about labour in spontaneous vaginal breech at term. They have attempted to construct normal curves for this group of women in both nulliprous and multiparous women. Another aim was to compare the curves for different types of breech presentation which is certainly quite unique.

This was a retrospective single centre experience in a french maternity unit. This design gives certain advantages but also adds some limitations in terms of relevance to other units with different management protocols for breech presentation at term.

Abstract

The abstract is succinctly written with all the basic information that is required for a good overview of the article.

Methods

The methodology is laid out very clearly and the statistical analysis is similar to that used by Zhang’s Safe Consortium group, which has been well validated.

I have some problems with the chosen criteria for an attempt at vaginal breech birth :

• Pelvimetry is an unproven intervention with no clear advantages but I accept that in some countries it is mandatory.

o We lack high quality data for this intervention which can of course increase the risk of harm to the mother and the baby

o The only outcome changed by pelvimetry is the rate of caesarean which unfortunately increases in the wrong hands – an excuse for a caesarean for the nervous obstetrician

�  Probably not the case for this group but the message can be misinterpreted

o I assume that multiparous women with previous normal vaginal deliveries were not also subjected to this intervention ? The text seems to allude that this was reserved for only the nullips which is reassuring.

�  This group have already performed the best possible test of pelvic capacity – childbirth

So, given the lack of proof, performing a CT scan in pregnant women, thus increasing the oncogenic risk for both the mother and the baby seems somewhat illogical and without doubt breaks the ‘primum non nocere’ rule.

If there is a real need to do this to reassure the team then why not an MRI which carries no risk ?

Perhaps this was not freely available to the authors.

They also include a Magnin index which is not widely used. This is also not recommended by the CNGOF. Why was this deemed necessary ?

The upper fetal weight estimate for an attempt was macrosomia presumably based on either a percentile of >P90 or an estimate of >4kg. It is not clear which definition has been used.

There was no lower limit for an attempt in contrast to the PREMODA criteria. Did the authors allow inclusion of growth restricted fetuses ? These were the babes that did so badly in the Term Breech Trial. This is important in order to correctly interpret the results as presented.

I am interested to know why the authors choose to present the cervical dilatation velocity as quartiles rather than percentiles : P5, P50 and P95. Not a criticism merely a question.

Results

The results are clearly expressed and well presented in both the written text and the tables, although the figures could perhaps be altered in the final draft to improve their interpretation/understanding. Perhaps it was the PDF summary that I received that made this more difficult.

As mentioned elsewhere, for me the lack of a complete perinatal outcome data is an important omission. I realise that the objective of the study was to merely produce some labour curves, not nomograms, for breech delivery but it is important to know if there were any negative consequences of this single centre’s obstetric practices. This will only be possible with full and transparent outcome reporting. My concern is that if this article is published without this information, others may be tempted to use these curves for guidance in the future, so this is paramount.

Discussion

The study is appropriately discussed in the context of previously published work also in reference to various national organisations for vertex and non-vertex presentations at term.

Lines 221-224 -the authors make an important comment on the lack of protocols for vaginal breech deliveries. A very relevant critique but not one that the authors themselves have addressed in this article, unless there is an appendix to which I do not have access. It is imperative that the specific management protocol used during the study period is made available in order to fully understand the results obtained and their relevance to other maternities. The supposition of the authors in the discussion section – lines 233-235 - would already have been determined had there been a standardised protocol for the management of breech in labour during the period of this study (single centre).

Nonetheless the findings of subtle differences for nulliparous women with breech presentations in the active phase of labour are interesting and worthy of note despite the high rate of oxytocin use in this study. This could be useful to others when constructing their own breech-specific protocols.

If the authors could demonstrate that the increase rate of success of vaginal birth in breech presentations (81% of the selected cases) with liberal use of oxytocin did not increase perinatal complications, then this would be something that could dramatically change clinical practice. It is therefore essential that this data be included in the article if it is available.

The information regarding the type of breech is very reassuring for those who have been deterred by certain presentations. As the authors mention, this agrees with the recently published FRABAT study. We need more supportive quality data like those presented here, in order to reverse the worrying trend away from vaginal breech delivery.

In terms of the authors interpretation of the limitations of the study I do not necessarily agree with them that the exclusion of women with a history of previous CS is a negative. Given the aggressive management of these labours, in combination with breech presentations, I would have had concerns about the risk of scar complications if these women had been included during this period.

Notwithstanding my concerns about the lack of a published protocol and the excessive use of oxytocin, I think that I would agree with the authors conclusions of their study in terms of the confirmation of the two distinct phases of labour – as for vertex presentations - and the need to consider progression in the context of parity. The data is also reassuring with regard to complete/incomplete breech’s.

Main problems with study

• Given the excessive use of syntocinon (77%) in both primiparous and most surprisingly multiparous women, the lack of an explanation or inclusion of the authors management protocol for labour in these cases is a serious omission. This probably means that the use of syntocinon is almost systematic for breech presentations, rather than being based on a careful clinical evaluation.

• As the study was performed in a single centre I am sure that a management protocol could be made available for publication as an appendix. Otherwise it is very difficult to understand the curves in the context of what appears to be in the majority of cases, augmented or perhaps in some, induced labours.

o This omission makes interpretation of the curves and the validity of the curves for use in other maternities very problematic.

• Many questions remain such as

o What criteria were used for the use of oxytocin augmentation ?

o Was this just lack of regular contractions as alluded to in the text or was this also based on lack of progress.

o What was the definition of lack of progress or stagnation/dystocia ?

o How frequent were the vaginal examinations – hourly, 2 hourly or 4 hourly ?

o Was augmentation restricted only to the active phase of labour or was it also used at less than 5 cm ?

o What is the policy on the use of oxytocin in the second stage of labour ? Some units in France start oxytocin systematically in the second stage if it has not already been started before. This in not normal practice elsewhere.

o Do the authors have more complete date for maternal and neonatal outcomes ?

�  No maternal data is included although episiotomy and bleeding is mentioned in the methodology section, so I assume that this data was collected.

�  More neonatal data is required.

o This is important as the very impressive vaginal delivery success rate of 81% could have come at a significant cost to both the mother of the baby

• There are several minor grammatical and syntax errors that need to be addressed.

The authors may argue that the study was pragmatic and therefore more applicable to real-world clinical practice but without some of this missing information, it would be difficult for others to adopt these curves into their own services.

I do not wish to be too negative about the article as I think that it is actually really important to help us move forward in the fight to promote vaginal breech delivery around the world. The data shows that such an option it’s viable in the right hands but full outcome date would be more reassuring for sceptical colleagues.

Due to the importance and uniqueness of this work, if the authors can provide some answers to the questions that I have posed, then I would reconsider publication of a heavily revised maunscript.

COMMENTS FOR AUTHORS

The authors are to be congratulated on this very important piece of work.

At a time when people look for excuses to avoid vaginal breech delivery rather than considering this as a genuine option, this article provides interesting and in some ways reassuring data on the normal progress (with a lot of syntocinon) during a spontaneous breech labour.

Only the lack of complete outcome data and a copy of their own protocol for the management of a breech labour limits the power, validity and extrapolation of the findings.

The minor grammatical and syntax errors can easily be corrected.

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20 Jul 2021

Dear Drs.,

We would like to thank you for allowing us to revise and resubmit our manuscript toPLOS ONE. The reviewers’ comments are highly appreciated and have been constructive and conducive to developing an optimized manuscript. We have attached a “point-by-point” response below and made the corresponding changes to the manuscript. We believe that the changes have made our paper more suitable for publication in your esteemed journal.

Sincerely,

Dr. Benmessaoud on behalf of the coauthors

Response

Reviewer #1

Thank you for the opportunity of reviewing this very interesting paper. The authors aimed to describe the course of labor for breech delivery with comparison according the parity and the type of breech (frank or complete). The overall message is that the course of labor is similar to the one described for vertex presentation without significant impact on the type of breech. This result is very interesting and original. It should have a clinical impact by reducing the level of intervention for stagnation in case of breech delivery and might contribute to reduce the CS rate in this situation. I only have few comments for discussion.

Thank you for your comments and suggestions. We appreciate the time you invested in reviewing our manuscript and for providing us with an opportunity to improve it with the revised version.

Abstract

1. Indicate in the abstract if the difference according parity is significant or not

The cervical dilatation rate was slower than 1 cm/hour in the latent phase and faster than 1 cm/hour in the active phase. In the active phase, the median speed of cervical dilation was 1.67 cm/h [1.25, 2.61] (2 cm/h for multiparas and 1.54 cm/h for nulliparas). The parity difference was significant in the active phase (p<0.05).

This data has been added to the abstract.

Main text

2. How do the authors interpret the surprising difference between multiparous and nulliparous women with a higher speed of dilatation in the active phase?

We made an error when transcribing the data from Table 3 into the text. The overall dilation rate and the active phase dilation rate were faster in multiparous women. The speed of dilatation from 5 to 10 cm was 2 cm/h for multiparous women compared to 1.54 cm/h for nulliparous women, which is more logical.

3. Does your population include women with history of CS? Which proportion? Why not including cesarean section during labor for failure of progress for a secondary analysis (at least those at full cervical dilatation) and compare the dilatation curse between those who deliver vaginally and those with CS for failure of progress?

Regarding the data on previous cesarean sections, we did not collect this information. A history of cesarean section was not an exclusion characteristic. Cesarean sections may exist in the study’s population, but we are unable to confirm if this is the case.

We excluded patients who delivered by cesarean section during labor because we wanted to compare our curves to Zhang’s reference curves. We established our protocol according to Zhang's reference study, which excluded cesarean sections.

4. I’d like a more important discussion about our management in labor ward. Indeed, it is widely reported that a breech delivery has to be a “fast and easy delivery”. Your results support the opposite and that finally the course of labor is not very different between a vertex or breech presentation. Discuss that your results suggest that we might consider reducing our level for intervention in case of breech delivery for stagnation of dilatation especially for this latency phase that must be respected. This might be moderate for the second stage of labor for whom a longer duration of this stage might be an alarm signal for dystocia and lead to consider CS. Provide a short and concise conclusion by the end of the conclusion

The journal imposes a word count for a scientific article. However, we have modified the discussion and the conclusion according to your suggestions.

Reviewer #2

Thank you to give me to opportunity to review this work about labor progression of breech presentation at term. However, I remain perplex because it seems difficult to conclude about labor curves from a sample of 349 breech presentation in a single center. Moreover, lacking data (or not presented in the manuscript) did not allow us to draw conclusions and extrapolate the results.

Thank you for your comments and suggestions. We appreciate the time you invested in reviewing our manuscript and for providing us with an opportunity to improve it with the revised version.

1. The high rate of oxytocin use (77%) limits extrapolation of the results. Author should consider to stratify analyses with and without oxytocin use.

The population is not significant enough to allow for stratification. Stratification within the population (349 patients) will not be significant.

However, we collected times for introducing oxytocin during labor. We can add complementary data according to your recommendations. Oxytocin was introduced in the latent phase for 39 patients (14.4%), in the active phase for 150 patients (55.5%) and finally during the 2nd stage for 81 patients (30%).

The use of oxytocin is described in the protocol. Only 14.4% of patients received oxytocin in the latent phase. This result is reassuring for our practice. Recommendations to decrease oxytocin use are recent for cephalic delivery.

However, in view of the French recommendations and these first studies describing breech labor, a reflection on oxytocin use can be considered secondarily.

To consider modifications and secondary reflections, a first descriptive study, such as ours, was needed. Currently, the literature does not provide any analysis of breech labor regardless of the oxytocin rate used according to our protocol. Moreover, the low rate of neonatal and maternal complications despite a high oxytocin rate reassures us about the current use of oxytocin according to our protocol. As a reminder, oxytocin for augmentation was used in nearly half of the women included in the Consortium on Safe Labor and 74.9% in the PREMODA Study (8). It is possible that the high rate of labor augmentation reported in our study suggests more of a prophylactic than a therapeutic role.

This study’s purpose is not to provide guidelines for breech delivery but to provide a first description of breech labor and to open the discussion on vaginal breech delivery management.

We are aware that further studies are necessary.

2. How did the author define the onset of labor from their data?

The World Health Organization's definition of onset of labor was used for this work. The latent phase is a period characterized by painful uterine contractions and variable changes in the cervix with some degree of effacement and slow progression of dilation up to 5 cm. The active phase of labor is a period characterized by regular painful uterine contractions, a significant degree of cervical effacement and dilation up to 5 cm.

3. The beginning of the active phase of labor is 3 cm in this paper. The author should change this threshold for 5 or 6 cm as demonstrated in Zhang’s publication.

Like Zhang’s publication, we determined an active phase of labor at 5 cm.

In the results, we precisely state that “The first stage of labor progression was divided into a latent phase from 0 to 5 cm of dilation and an active phase from 5 to 10 cm.”

4. I do not understand why the authors decided to exclude cesarean deliveries. Why did they not choose the censure of these data? It would be necessary to include all women reaching the second stage of labor

Indeed, we excluded cesarean sections during labor because we established our protocol according to Zhang’s reference study, which excluded cesarean sections.

We hoped to create curves we could compare to Zhang’s reference cephalic curves. We agree that including cesarean sections during labor adds value to the statistical analysis. Caesareans could be the subject of a secondary analysis.

5. Please describe the protocol of oxytocin use during labor in breech presentations in the center in the material section. Because this protocol is not provided, extrapolation of the data is questionable.

The protocol is available in the appendix.

6. Neonatal issues are also questionable. How explain the high rate of neonatal transfers: 17.5% in multiparous and 10.8% in nulliparous women. A description of transfer indications is lacking. Apgar score should be reported as percentages of newborn with 5 minutes Apgar score <7 in Table 1. Moreover, please provide information about arterial pH at birth (mean and rate <7.0, <7.10 …)

The transfer rate is lower than national figures since the 2016 perinatal survey when the transfer rate of newborns in metropolitan France was 9.9%, which included 2.4% in child intensive care units and 4.2% in neonatology (12). In our study, 3.15% of newborns were transferred, of which 2.00% (n=7) were transferred to the neonatology unit and 1.15% (n=4) to the intensive care unit. The arterial pH was significantly lower, averaging 7.13 in nulliparous women versus 7.16 in multiparous women (p=0.013). The arterial lactate level was higher in nulliparous women: 6.54 mmol/l on average versus 5.20 mmol/l on average in multiparous women (p<0.001). Concerning the 4 newborns transferred to the intensive care unit, 3 had an arterial pH<7, and one had an arterial pH of 7.20; however, the Apgar scores were >7 at 5 min. For 7 of the newborn babies transferred to neonatology, only 1 had an Apgar score <7 at 5 min with an arterial pH of 7.05. A total of 4 of the newborn babies had a pH <7.05. Lactate levels were >10 mmol/L for 2 of them.

7. In the results section, a description of labor management is lacking: cervical dilation at admission in labor ward unit, rate of amniotomy, cervical dilation when oxytocin was started … Without a such description of labor practices, extrapolation of these results remains questionable.

We added these parameters to the data and to the protocol in the appendix.

8. Table 3, last line (from 9 to 10), the significance of the comparison between complete and franck breech is probably wrong: p=0.017???

The statistical analysis confirms these results.

9. In the conclusion of abstract and the manuscript, please delete “when there is adequate management”. This subjective comment seems inappropriate considering the high rate of oxytocin use and the high rate of neonatal transfer.

Management is described in the protocol. We would like to point out that the transfer rate is lower than the national transfer rate.

We collected the times for introducing oxytocin during labor. We added complementary data according to your recommendations. Oxytocin was introduced in the latent phase for 39 patients (14.4%), in the active phase for 150 patients (55.5%) and finally during the 2nd stage for 81 patients (30%).

The use of oxytocin is described in the protocol. Only 14.4% of patients received oxytocin in the latent phase. This result is reassuring for our practice. Recommendations to decrease oxytocin use are recent for cephalic delivery.

However, in view of the new recommendations and these first studies describing breech labor, a reflection on the use of oxytocin can be considered secondarily.

To consider modifications and secondary reflections, a first descriptive study, such as ours, was needed. Currently, the literature does not provide any analysis of breech labor regardless of the rate of oxytocin used according to our protocol.

Moreover, the low rate of neonatal and maternal complications despite a high oxytocin rate reassures us on the current use of oxytocin according to our protocol. Indeed, oxytocin is administered late in labor. However, a reflection on the use of oxytocin in cephalic and breech births should be pursued. However, our main objective is to counteract the high rate of cesarean section by first describing breech vaginal delivery.

This study’s purpose is not to provide guidelines for breech delivery but to provide a first description of breech labor and to open the discussion on vaginal breech delivery.

We are aware that further studies are necessary.

10. In the introduction section, please delete in lines 93-94 “12/30/2020 2:17:00 PM” and change the police in lines 102-108

These points have been corrected.

11. In the materials and methods section, please provide the ethic registration number

Under French regulations, the study was exempt from institutional ethics review because it was an observational study using anonymized data from medical records. The women were systematically informed that the obstetrical and neonatal data could be used for to evaluate medical practices and were explicitly informed that they could sign an opposition form.

Reviewer # 3

The authors performed this study in order to assess cervical dilatation length during the passive and active labor of women presenting with a fetus in breech position. The primary objective was to evaluate labor progression of primiparous and multiparous women in cases of breech presentation as labor curves in such cases are not available. The secondary outcome was to determine whether the type of breech or parity can influence the speed of cervical dilatation. This retrospective study was performed in a single French center between 2010 – 2018. The inclusion criteria were: women eligible after 37 weeks of gestation with a live breech presentation if the onset of labor was spontaneous and if they completed the first and second stages with a vaginal delivery. The authors collected labor progression patterns by examining the relationship between the elapsed times from the full dilatation and cervical dilatation stages. The labor durations (min) was characterized by examining the distribution of time intervals from one cervical dilatation stage to the next and ultimately to full dilatation. The median, first quartile and third quartile of the cervical dilatation velocity were calculated.During the study period 3.3 % of the presentation were breeches. A total of 495 (76.1%) women with a breech presentation on 650 attempted a vaginal delivery. The authors illustrate the different velocities of cervical dilatation depending on parity, type of breeches and passive/active phase. Overall, the clinical topic is interesting as labor curves in case of breech presentation has not been previously publish. The methodology of this study is sound. Furthermore, the discussion is well constructed, and the authors address the limits of their study.

Thank you for your comments and suggestions. We appreciate the time you invested in reviewing our manuscript and for providing us with an opportunity to improve it in the revised version.

1. Proof-reading by native English speaker is mandatory, in order to improve its readability and correct several typos.

The English was proofread by a certified translation agency. However, a second proofreading has been performed based on your recommendations.

2. Introduction: Line 93-94: “12/30/2020 2:17:00 PM”. Line 101 – 108 : the police is different than from the rest of the text.

These points have been corrected.

3. Methods:

Line 140: Why was the episiotomy and total volume of bleeding rate collected as it is not presented in the results?

We selected hemorrhage and lesions of the perineum as well as episiotomy as maternal complications that occur during vaginal delivery. The results are not presented but have been added to Table 1.

4. Table 1: Please precise if the numbers are median (IQR) or mean (SD).

The numbers are mean (SD). This information has been added to the manuscript.

Reviewer # 4

This is a unique study and is the first attempt to create labour curves for spontaneous vaginal breech delivery at term. The authors must be highly commended for this very valuable and important piece of work. As someone who is a proponent of vaginal breech this is certainly a very interesting and new approach that could be built on in the future.

However, given the single centre design, the seemingly aggressive use of syntocinon, which has not been explained, and the lack of complete outcome data, more work is needed before these curves could be used in other centers which may have more physiological approaches to childbirth.

Background

The authors have corrected and identified a gap in our knowledge about labour in spontaneous vaginal breech at term. They have attempted to construct normal curves for this group of women in both nulliprous and multiparous women. Another aim was to compare the curves for different types of breech presentation which is certainly quite unique. This was a retrospective single centre experience in a french maternity unit. This design gives certain advantages but also adds some limitations in terms of relevance to other units with different management protocols for breech presentation at term.

Abstract

The abstract is succinctly written with all the basic informations that is required for a good overview of the article.

Methods

The methodology is laid out very clearly and the statistical analysis is similar to Zhang’s Safe Consortium group, which has been validated.

Thank you for your comments and suggestions. We appreciate the time you invested in reviewing our manuscript and for providing us with an opportunity to improve it in the revised version.

I have some issues with the chosen criteria for a vaginal breech delivery attempt:

1. Pelvimetry is an unproven intervention with no clear advantages but I accept that in some countries it is mandatory. We lack high quality data for this intervention which can of course increase the risk of harm to the mother and the baby.

The only outcome changed by pelvimetry is the rate of caesarean which unfortunately increases in the wrong way – an excuse for a caesarean for the nervous obstetrician. Probably not the case for this group but the message can be misinterpreted. I assume that multiparous women with previous normal vaginal deliveries were not subjected to this intervention? The text seems to allude that this was reserved for nulliparous only which is reassuring. This group has already performed the best test of pelvic capacity – childbirth

So, given the lack of proof, performing a CT scan in pregnant women, thus increasing the oncogenic risk for both the mother and the baby seems somewhat illogical and without doubt breaks the ‘primum non nocere’ rule.

If there is a real need to do this to reassure the team then why not an MRI which carries no risk? Perhaps this was not freely available to the authors.

They also include a Magnin index which is not widely used. This is also not recommended by the CNGOF. Why was this deemed necessary?

Pelvimetry is used in our local practice more often than the national college uses it. In our practice, it is a parametric analysis and morphological analysis of the pelvis.

Multiparous patients who have already delivered do not require pelvimetry in our center.

Pelvimetry is not systematic and is discussed according to the previous mode of delivery and the fetal weight at birth. We agree with your opinion regarding the interest in pelvic MRIs. Unfortunately, this imaging is not easily accessible in our institution. The CT scans performed are low-dose scans.

2. The upper fetal weight estimate for an attempt was macrosomia presumably based on either a percentile of >P90 or an estimate of >4kg. It is not clear which definition has been used.

There was no lower limit for an attempt in contrast to the PREMODA criteria. Did the authors allow inclusion of growth restricted fetuses? These were the babes that did so badly in the Term Breech Trial. This is important in order to correctly interpret the results as presented.

Suspected fetal macrosomia was considered for a fetal estimation weight >3800 g. This information has been added to the protocol. In our hospital, we do not use a lower weight limit because the center performs breech vaginal deliveries for premature delivery.

In our population, 26 fetuses weighed <2500 g, and 7 fetuses weighed <2300 g.

3. I am interested to know why the authors choose to present the cervical dilatation velocity as quartiles rather than percentiles: P5, P50 and P95. Not a criticism merely a question.

We thank reviewer for raising this point. We indeed expressed cervical dilatation velocity as a median and interquartile range rather than percentiles to provide the reader with a more precise indicator of data distribution. Mean and standard deviation would not be appropriate due to the fact that velocity distribution was not always perfectly bell shaped and symmetrical. However, the interquartile range contrary to the P5 and P95 is not affected by extreme values and tells the reader more precisely how the middle 50% of the observations are spread out.

Discussion

4. The study is appropriately discussed in the context of previously published work also in reference to various national organisations for vertex and non-vertex presentations at term. Lines 221-224 -the authors make an important comment on the lack of protocols for vaginal breech deliveries. A very relevant critique but not one that the authors themselves have addressed in this article, unless there is an appendix to which I do not have access. It is imperative that the specific management protocol used during the study period is made available in order to fully understand the results obtained and their relevance to other maternities.

o What criteria were used for the use of oxytocin augmentation ?

o Was this just lack of regular contractions as alluded to in the text or was thisalso based on lack of progress.

o What was the definition of lack of progress or stagnation/dystocia ?

o How frequent were the vaginal examinations – hourly, 2 hourly or 4 hourly ?

o Was augmentation restricted only to the active phase of labour or was it also used at less than 5 cm ?

o What is the policy on the use of oxytocin in the second stage of labour ? Some units in France start oxytocin systematically in the second stage if it has not already been started before. This in not normal practice elsewhere.

The above remark is relevant. Indeed, it is necessary to specify these various elements. We answer all of the above questions in our protocol, which is available in the appendix.

We collected the times for introducing oxytocin during labor, and we added the additional data to the manuscript. Oxytocin was introduced in the latent phase for 39 patients (14.4%), in the active phase for 150 patients (55.5%), and finally during the 2nd stage for 81 patients (30%).

5. Do the authors have more complete date for maternal and neonatal outcomes?

No maternal data is included although episiotomy and bleeding is mentioned in the methodology section, so I assume that this data was collected.

More neonatal data is required. This is important as the very impressive vaginal delivery success rate of 81% could have come at a significant cost to both the mother of the baby

Indeed, we collected data on maternal complications concerning perineal lesions and postpartum hemorrhage.

These data were removed to correspond with the review criteria that limited the amount of information. We added this information to the manuscript.

To expand neonatal data, we added data concerning the average pH and lactate level at birth according to parity.

The transfer rate is lower than national figures since the 2016 perinatal survey when the transfer rate of newborns in metropolitan France was 9.9%, which included 2.4% in child intensive care units and 4.2% in neonatology (12). In our study, 3.15% of newborns were transferred of which 2.00% (n=7) were transferred to neonatology and 1.15% (n=4) to intensive care.We compared the average using parity.

The arterial pH was significantly lower, with an average of 7.13 in nulliparous women versus 7.16 in multiparous women (p=0.013). The arterial lactate level was higher in nulliparous women: 6.54 mmol/L on average versus 5.20 mmol/L on average in multiparous women (p<0.001).

Concerning the 4 neonates transferred to the intensive care unit, 3 had an arterial pH <7, and one had an arterial pH of 7.20, but its Apgar score was <7 at 5 min.

For 7 of the neonates transferred to neonatology, only 1 had an Apgar score <7 at 5 min with an arterial pH of 7.05. A total of 4 of the neonates had a pH <7.05. Lactate levels were >10 mmol/L for 2 of them.

Submitted filename: Response to the reviewer final version - copie.docx

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16 Nov 2021

5 Dec 2021

You noted inconsistent statements regarding the ethics approval and informed consent of our study entitled "Analysis of spontaneous labor progression of breech presentation at term".

In the manuscript, we have clarified ethical approval.

Under French regulations, the study was exempt from institutional ethics review because it was an observational study using anonymized data from medical records. The women were systematically informed that the obstetrical and neonatal data could be used for to evaluate medical practices and were explicitly informed that they could sign an opposition form.

All women giving birth in our maternity are informed that their anonymous medical data can be used for any retrospective research projects. The information and the opposition forms were approved by our local ethical committee CPP Est II (original approval document attached)

The authors received no specific funding for this work.

16 Dec 2021

Analysis of spontaneous labor progression of breech presentation at term

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8 Feb 2022

PONE-D-20-40976R2

Analysis of spontaneous labor progression of breech presentation at term

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