First stage progression in women with spontaneous onset of labor: A large population-based cohort study

Louise Lundborg; Katarina Åberg; Anna Sandström; Andrea Discacciati; Ellen L Tilden; Olof Stephansson; Mia Ahlberg

doi:10.1371/journal.pone.0239724

. 2020 Sep 25;15(9):e0239724. doi: 10.1371/journal.pone.0239724

First stage progression in women with spontaneous onset of labor: A large population-based cohort study

Louise Lundborg ^1,^*, Katarina Åberg ¹, Anna Sandström ^1,^2,^3,⁴, Andrea Discacciati ^5,⁶, Ellen L Tilden ^4,⁷, Olof Stephansson ^1,², Mia Ahlberg ^1,²

Editor: Roger C Young⁸

PMCID: PMC7518577 PMID: 32976520

Abstract

Objective

To describe the duration, progression and patterns of first stage of labor among Swedish women.

Design

Population-based cohort study.

Population

Data from Stockholm-Gotland Obstetric Cohort 2008–2014 including ¼ of all births in Sweden, the final sample involved a total of 85,408 women with term, singleton, vertex, live fetuses experiencing spontaneous labor onset and vaginal delivery with normal neonatal outcomes.

Main outcome measures

Time to progress during first stage of labor using three approaches: 1) Traverse time in hours to progress centimeter to centimeter, 5^th, 50^th (and 95^th percentile); 2) Dilation curves for different percentiles, and; 3) Cumulative duration for the 95^th percentile by parity and dilation at admission.

Results

Variation in both the total duration and the trajectory of cervical change over time is large. Similar to the general held view, the rate of cervical dilation accelerates at 5–6 centimeters. Among nulliparous women, the median time found in our population was faster than their counterparts in studies conducted on American and African cohorts. Among nulliparous and multiparous women our data suggest that the median cervical change over time is faster than 1 cm per hour during the first stage of labor. However, traverse time of cervical change at and beyond the 95^th percentile is longer than 1 cm per hour.

Conclusions

Labor progression varies widely and labors experiencing a prolonged first stage can still result in normal outcomes. The assumption of 1 cm per hour cervical dilation rate for the first stage of labor may not be universally meaningful. There are differences in progression for women during first stage of labor in different populations. For prolonged labor progression to be more clinically meaningful, the association with adverse birth outcomes needs to be further investigated in specific populations.

Introduction

Friedman introduced the first graphic analysis of labor progress in the 1950's [1, 2]. Based on the Friedman labor curve, Philpott and colleagues [3, 4] developed guidelines to monitor labor and detect deviating labor progression. Influenced by the work of both Friedman [1, 2, 5, 6] and Philpott [3, 4] the World Health Organization (WHO) partograph was constructed [7]. The partograph`s alert line represent cervical dilation of 1 cm per hour and an action line is placed after the alert line, usually after two to four hours. The assumption that normal labor progression is linear has had a huge impact on labor management globally over the last 50 years. Several actions have been made to expedite birth when labor continues longer than thresholds deemed ‘labor dystocia’ by this traditional partograph [8–11]. The cesarean delivery rate has increased worldwide, and one major reason for this increase is cesarean delivery due to slow labor—labor dystocia [12–16]. Sweden has a similar increase but differs with an overall lower rate, approximately 18% of deliveries are via cesarean, compared with many other high-income countries [17–20]. Over the last decade, both the strict timelines recommended by the traditional partograph and the shape of the labor curve have been challenged [21–27]. In 2010, Zhang and colleagues presented a hyperbolic labor curve with faster progression after 6 cm, suggesting that some cesarean deliveries due to labor dystocia early in labor could be prevented [26]. Further examination of this question in other populations and with large data sets is needed to advance this line of inquiry. Swedish healthcare systems routinely collect granular, population level data. This presents a unique opportunity to conduct epidemiological maternity care research.

We conducted a large (n = 175,522) population-based register cohort study, using the same selection criteria and similar statistical methods as two recent studies on contemporary populations conducted by Zhang et al. [26] (n = 62,415, American cohort) and Oladapo et al. [23] (n = 5606, African cohort). The purpose of this study was to refine this emerging contemporary understanding of “normal” labor progression through describing: 1) the duration of the first stage labor, evaluating both duration to progress from one centimeter of cervical dilation to the next as well as the total duration, and 2) trajectories of cervical dilation by various quantiles in Swedish women with term, singleton, vertex, live fetuses experiencing spontaneous labor onset and vaginal delivery with normal neonatal outcomes.

Material and methods

Data were obtained from the population-based Stockholm-Gotland Obstetric Cohort, a data base that captures information directly from the electronic medical record system Obstetrix on about 25% of all pregnancies and deliveries in Sweden. This data base includes prospectively collected variables regarding maternal characteristics, maternal medical history, processes and care from pregnancy through birth, as well as neonatal health and care. All care in this setting is free of charge during pregnancy and childbirth, and more than 99.9% of all women give birth in a hospital. In this setting, antenatal care is offered to all women. The first visit generally takes place between 7 to 12 weeks of gestation, with approximately 10–12 visits during pregnancy depending on parity. Midwives are the primary caregivers in Sweden, and women are referred to obstetricians when needed. The Stockholm-Gotland Obstetric database further contains granular information regarding the onset of labor, labor management including detailed information from the partograph such as time points for cervical dilation, cervical exams, epidural analgesia use, and oxytocin for labor augmentation, mode of delivery, infant characteristics, and maternal and neonatal diagnoses according to the International Classification of Diseases, 10th revision (ICD-10).

Between January 2008 and October 2014, data regarding 175,522 pregnancies and births was collected. We included 85,408 women with term (37+0 until 41+6 weeks of gestation), vertex, singleton pregnancies who experienced spontaneous labor onset with a live fetus. We excluded women whose labors were induced or who delivered via cesarean section or had a previous cesarean delivery. We also excluded women with less than two cervical examinations during first stage and records in which timing of the complete dilation of cervix was missing to be able to create labor curves in a reversed approach from fully dilated cervix. As our intent was to describe labor processes among those with uncomplicated outcomes, we also excluded births when neonates had an Apgar score less than 7 at 5 minutes of age or any of the following morbidities assessed by ICD-10 diagnostic codes: hypoxic ischæmic encephalopathy (HIE) (P916A, P916B, P916C, P916X), convulsion (P909, P909A, P909B, P909C) and meconium aspiration (P240). Fig 1 describes the sample selection process for the study cohort.

Fig 1 — Gestational age was determined using the following hierarchy: (a) embryo transfer, (b) first trimester ultrasound (c) early second trimester ultrasound offered to all women, (d) date of last menstrual period and (e) postnatal assessment. Characteristics of the study populations are reported as frequencies and percentages for categorical variables and as means and standard deviations or as medians and 10^th, 90^th percentiles for continuous variables, as indicated (Table 1).

With focusing on nulliparous women, the start of first stage of labor was defined by two strict criterions: C1) time characterized by well effaced cervix (complete or nearly 100% effacement), cervical dilation of ≥3 centimeter in presence of regular painful uterine contractions or alternatively C2) time characterized by well effaced cervix (complete or nearly 100% effacement), a rupture of membrane in combination with cervical dilation of ≥3 centimeter. Following this hierarchy of the two criterions, when there were two or three time points fulfilled in one criterion, the second time point was chosen as the starting point of first stage of labor. If a woman did not fulfill all the parameters of criterion one, she was evaluated according to criterion two. Women who did not fulfill criterion one or two were not included in the study cohort since the onset of the first stage of labor could not be clearly defined. These criterions are based on the Swedish standard practice to identify women who are in first stage of labor and used as a guideline at admission at all obstetric units in the cohort [28]. The termination of the first stage was defined by the time-point that the cervix was fully dilated. The estimated median duration of the first stage of labor was extrapolated from the cervical examination on admission and subsequent examinations performed during labor. Labor duration prior to hospital admission was not considered in this analysis.

To explore potential selection bias, we also conducted analyses with a cohort including women delivered via cesarean section and adverse neonatal outcomes. Our intent with this step in the analysis was to describe characteristics, first stage duration and the trajectory of cervical change among women regardless mode of delivery or adverse birth outcome. In this target population cohort, we included 101 730 women with term (37+0 until 41+6 weeks of gestation), vertex, singleton pregnancies who experienced spontaneous labor onset with a live fetus.

The starting point of first stage was defined identical as for the above described cohort. The endpoint was either time point for fully dilated cervix or time point for cesarean delivery.

S1 Fig describes the sample selection process for the target population cohort.

Statistical analysis

Three approaches were used to describe the duration of first stage of labor and the trajectory of cervical change: 1) Traverse time in hours to progress centimeter to centimeter, 5^th, 50^th (median) and 95^th percentile; 2) Dilation curves for different percentiles of cervical dilation, and; 3) 95^th percentile of cumulative duration of labor stratified by parity and dilation at admission.

Women were categorized into three parity groups (0,1, and 2+) to explore any differences according to parity. Labor duration and the trajectory of cervical change were characterized at every centimeter, starting at 3-centimeter dilation, during the first stage of labor. To estimate the distributions of traverse times, which are the duration to progress from one cm of cervical dilation to the next, we used interval censored regression under the assumption that traverse times followed log-normal distributions [29].

To construct labor dilation curves, the earliest recorded time of full cervical dilation was considered as the starting point or time zero, to anchor the curves. It was performed in an analysis similar to previous studies and time were calculated backwards: the axis was reverted to a positive value after computation [23, 25, 26]. Time points of cervical dilation were expressed as hours prior to the time of full cervical dilation. For example, if a measurement was performed 45 minutes prior to full cervical dilation, then time = 0.75 hours [29]. Since we were not only interested in mean cervical dilation duration, but rather in its distribution, we used quantile regression to estimate a set of quantiles (10^th, 25^th, 50^th, 75^th, 90^th, and 95^th) of cervical dilation conditional on time to complete cervical dilation. Of note, quantile regression does not make any assumptions about the conditional distribution of the outcome (here, cervical dilation) given covariates (here, time to complete dilation) Furthermore, since cervical dilation is a measure bounded between 0 and 10 cm, we performed quantile regression on a logit transform of cervical dilation. This method, which hinges on the fact that quantiles are invariant to monotone transforms, such as the logit, is known as logistic quantile regression [30]. Time to complete cervical dilation, the only covariate of our models, was modelled using restricted cubic splines with three knots [31].

To evaluate any presumptive differences in the duration of and trajectory of cervical change, we also estimated cumulative labor stratified by cervical dilation at admission and starting from 3, 4, 5, or 6 cm. This was done using an analogous interval-censored regression approach to the one used for traverse time estimation (Table 3, Figs 2–4). All statistical analyses were performed using Stata 14.2 (StataCorp, College Station, TX, USA). The regional ethical committee at Karolinska Institutet, Stockholm, Sweden approved the study protocol (No 2009/275-31, 2012/365-32, 2013/792-32, 2014/177-32, 2014/962-32). Written informed constent was not required by the ethical committee. All data were anonymized prior to access. The database is stored in the Unit of Clinical epidemiology at Karolinska Institutet Stockholm, Sweden.

Table 3. Cumulative duration of labor in hours in para 0, 1, and 2+ based on the cervical dilation at admission.

		Parity 0		1		2+
From cervical dilation	To cervical dilation	Duration in hours	N	Duration in hours	N	Duration in hours	N
3	4	0.81 (0.14, 4.88)	7 694	0.47 (0.05, 4.50)	3 220	0.53 (0.06, 4.70)	1 893
3	5	2.66 (0.78, 8.80)	7 661	1.66 (0.35, 7.90)	3 217	1.80 (0.39, 8.46)	1 895
3	6	3.89 (1.38, 10.98)	7 692	2.48 (0.65, 9.55)	3 222	2.56 (0.69, 9.80)	1 900
3	7	4.66 (1.72, 12.62)	7 689	2.88 (0.80, 10.35)	3 225	2.95 (0.81. 10.68)	1 903
3	8	5.27 (1.98, 14.04)	7 678	3.15 (0.91, 10.94)	3 223	3.15 (0.88, 11.23)	1 906
3	9	5.78 (2.20, 15.13)	7 701	3.35 (0.99, 11.38)	3 225	3.31 (0.95, 11.51)	1 906
3	10	6.21 (2.38, 16.23)	7 717	3.47 (1.03,11.70)	3 228	3.39 (0.97, 11.77)	1 906
4	5	0.89 (0.16, 5.16)	11 442	0.38 (0.04, 3.82)	5 711	0.44 (0.04, 4.56)	2 890
4	6	2.29 (0.63, 8.32)	11 442	1.18 (0.22,6.37)	5 710	1.23 (0.21, 6.95)	2 891
4	7	3.27 (1.05, 10.18)	11 452	1.77 (0.41, 7.70)	5 715	1.78 (0.40,8.03)	2 897
4	8	3.94 (1.34, 11.65)	11 473	2.09 (0.51, 8.56)	5 710	2.08 (0.50,8.60)	2 900
4	9	4.52 (1.58, 12.94)	11 488	2.33 (0.59,9.24)	5 714	2.27 (0.57, 9.02)	2 904
4	10	4.99 (1.76, 14.11)	11 520	2.48 (0.63,9.69)	5 720	2.38 (0.60,9.44)	2 905
5	6	0.66 (0.09, 4.61)	8 150	0.21 (0.02, 2.81)	5 725	0.21 (0.01, 3.31)	2 363
5	7	1.66 (0.38, 7.35)	8 149	0.69 (0.09, 5.00)	5 215	0.67 (0.08, 5.67)	2 366
5	8	2.51 (0.67, 9.35)	8 161	1.13 (0.20, 6.93)	5 220	1.10 (0.18, 6.92)	2 367
5	9	3.15 (0.90, 10.92)	8 163	1.49 (0.29, 7.13)	5 216	1.38 (0.25, 7.62)	2 368
5	10	3.65 (1.08, 12.33)	8 201	1.59 (0.33, 7.66)	5 224	1.50 (0.28, 8.14)	2 374
6	7	0.49 (0.05, 3.81)	5 783	0.11 (0.01,2.20)	5 232	0.10 (0.04,2.22)	1 864
6	8	1.22 (0.22, 6.77)	5 779	0.46 (0.05,4.29)	4 449	0.40 (0.04, 4.20)	1 861
6	9	2.09 (0.49, 8.93)	5 800	0.84 (0.13, 5.65)	4 457	0.70 (0.09,5.28)	1 867
6	10	2.67 (0.67, 10.70)	5 843	1.05 (0.17, 6.36)	4 466	0.85 (0.12, 5.90)	1 870

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Fig 2 — Labor curves with a reversed approach from fully dilated cervix in singleton term pregnancies with spontaneous onset of labor and vertex presentation, vaginal delivery and healthy neonates.

Fig 4 — Labor curves with a reversed approach from fully dilated cervix in singleton term pregnancies with spontaneous onset of labor and vertex presentation, vaginal delivery and healthy neonates.

Fig 3 — Labor curves with a reversed approach from fully dilated cervix in singleton term pregnancies with spontaneous onset of labor and vertex presentation, vaginal delivery and healthy neonates.

Results

Table 1 presents the characteristics of women and infants by parity. The majority of women had a spontaneous vaginal birth (nulliparous = 81.4%; parity 1 = 96.9%; parity 2+ = 96.5%). Nulliparous women were younger than those with one and two-plus parity, and composed 52% of the sample. Mean body mass index (BMI) increased by one unit with each advancing level of parity (23 vs. 24 vs. 25). Oxytocin for augmentation was used in almost half of the nulliparous women (49.1%), and use decreased to 24.1% in parity 1 and slightly less, 23.7%, in parity 2+. Epidural analgesia was used in 64.5% of the nulliparous women, 32.6% of women with parity 1, and 22.9% of women with parity 2+. Mean birth weight increased by about 150 grams from first to second-born infants but only by another 26 grams from the second-born to subsequent infants. Mean gestational age was similar across parity groups.

Table 1. Baseline characteristics of the study population by parity.

	Parity = 0 n = 44 813			Parity = 1 n = 27 722			Parity = 2+ n = 12 873
Characteristics		%	N		%	N		%	N
Age years, mean (SD)	29.2 (4.96)		44 783	31.6 (4.65)		27 707	34.1 (4.63)		12 872
Maternal height cm mean (SD)	166.6 (6.43)		44 358	166.4 (6.48)		27 480	165.5 (6.48)		12 754
BMI. kg/m² at first visit antenatal clinic	23 (3.94)		43 132	24 (4.35)		26 666	25 (4.68)		12 424
Family situation
Single		2.3	1 044		1.2	323		2.4	305
Co-habitant		90.3	40 454		95.2	26 403		92.5	11 902
Missing		7.4	3 315		3.6	994		5.2	666
Amniotic membranes status at admisson
Intact		65.8	29 494		75.6	20 946		76.4	9 840
Ruptured		32.2	14 443		22.6	6 259		21.7	2 798
Missing		2.0	876		1.9	517		1.8	235
*Cx dilation at admission** median 10^th,90^th)	5 (3,8)		44 813	5 (3,8)		27 722	5 (3,8)		12 873
*Cx exams during labor** median (10^th,90^th)	4 (2,7)		44 813	3 (2,7)		27 722	3 (2,5)		12 873
Oxytocin (%)
No		50.9	22 830		78.6	21 779		76.3	9 817
Yes		49.1	21 983		21.4	5 943		23.7	3 056
Epidural (%)
No		35.5	15 896		67.4	18 688		77.1	9 924
Yes		64.5	28 917		32.6	9 034		22.9	2 949
Mode of birth (%)
Non-instrumental vaginal birth		81.4	36 465		96.9	26 865		96.5	12 427
Instrumental delivery		18.6	8 348		3.1	857		3.5	446
Gestational length at birth mean (SD)	40.1 (1.09)		44 813	40.0 (1.07)		27 722	39.9 (1.12)		12 873
Birth weight in grams mean (SD)	3 474 (437.8)		44 788	3 640 (460.37)		27 709	3 666 (483.13)		12 868
Head circumference in cm mean (SD)	34 (1.73)		44 648	35 (1.74)		27 656	35 (1.68)		12 835
Fetal position (%)
Occiput anterior		96.8	43 390		96.3	27 704		96.5	12 427
Occiput posterior		3.2	1 423		3.7	1 018		3.5	446

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The estimated 5^th, 50^th, and 95^th percentiles of traverse times’ distributions, i.e. duration of labor from one centimeter to the next, using 3 cm as a starting point, are reported in Table 2. Traverse time in the 95^th percentile well exceeds 1 cm per hour at all stages in all parity groups. However, the 50^th percentile in both nulliparous and multiparous shows faster progression than 1 cm per hour at all stages. To support clinical translation, we also generated graphic representations that depict a random sample of numerous women’s labor curves, by parity and based on percentiles rather than average labor curves (Figs 2–4).

Table 2. Duration of labor in hours from one-centimeter dilation to the next, by parity.

		Parity 0		Parity 1		Parity 2+
Cervical dilation cm	Cervical dilation cm	Duration in hours (min-max)	n	Duration in hours (min-max)	n	Duration in hours (min-max)	n
3	4	0.83 (0.14–4.97)	8 876	0.47 (0.05–4.65)	3 566	0.52 (0.05–5.05)	2 152
4	5	0.89 (0.15–5.26)	17 425	0.38 (0.04–3.82)	7 550	0.43 (0.04–4.62)	4 113
5	6	0.68 (0.10–4.55)	19 017	0.23 (0.02–2.90)	8 962	0.19 (0.01–3.23)	4 454
6	7	0.48 (0.06–3.82)	17 969	0.12 (0.01–2.25)	8 887	0.10 (0.01–2.37)	4 135
7	8	0.33 (0.03–3.62)	16 599	0.08 (0.00–1.94)	8 470	0.05 (0.00–1.85)	3 717
8	9	0.24 (0.02–3.00)	16 326	0.04 (0.00–1.58)	8 233	0.02 (0.00–1.27)	3 500
9	10	0.18 (0.01–2.66)	14 611	0.02 (0.00–1.18)	5 990	0.01 (0.00–1.03)	2 357

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Data reported as median hours (5^th, 95^th percentiles)

Table 3 describes the cumulative duration of labor of women in the 5^th, 50^th, and 95^th percentiles. Results show that the estimated cumulative duration of time includes wide variation, consistent with the data previously displayed in Table 2. While those whose first stage of labor progression at the 50^th percentile showed cervical dilation trajectories of 1 cm per hour in all parity groups, those with first stage of labor progression at the 95^th percentile who were admitted at 3 cm showed a substantially longer first stage, lasting for >16 hours among nulliparous women and >11 hours among multiparous women. For women admitted at 4 cm, first stage duration among nulliparous women could last >14 hours and among multiparous women first stage duration was slightly less than 10 hours.

Figs 5–7 illustrate the 95^th percentiles of cumulative labor duration, plotted as staircase lines based on the cervical dilation observed at admission, and centimeter by centimeter until full cervical dilation. The staircase cumulative duration is equal to the 95^th percentiles in Table 3.

Fig 5 — Illustrate the 95^th percentiles of cumulative labor duration in parity = 0 and plotted as staircase lines based on the cervical dilation observed at admission, and centimeter by centimeter until full cervical dilation. The staircase cumulative duration is equal to the 95^th percentiles in Table 3.

Fig 7 — Illustrate the 95^th percentiles of cumulative labor duration in parity = 2+ and plotted as staircase lines based on the cervical dilation observed at admission, and centimeter by centimeter until full cervical dilation. The staircase cumulative duration is equal to the 95^th percentiles in Table 3.

Fig 6 — Illustrate the 95^th percentiles of cumulative labor duration in parity = 1 and plotted as staircase lines based on the cervical dilation observed at admission, and centimeter by centimeter until full cervical dilation. The staircase cumulative duration is equal to the 95^th percentiles in Table 3.

S1 Table presents the characteristics of women and infants by parity in the target population cohort. The majority of women regardless of parity had a spontaneous vaginal birth. Among nulliparous 70.9% had a spontaneous vaginal birth and 11,4% (6 451 women) had a cesarean delivery. For parity 1 94,5% had a spontaneous vaginal birth and 2.1% (604 women) had a cesarean delivery. Posterior fetal position was 6.1% for nulliparous, 4,2% for parity 1 and 3,8% for parity 2+. The estimated 5^th, 50^th, and 95^th percentiles of traverse times’ distributions, i.e. duration of labor from one centimeter to the next are reported in S2 Table. Traverse time in the 95^th percentile well exceeds 1 cm per hour at all stages in all parity groups and the estimated duration exceeds the corresponding distributions in the study cohort. S3 Table describes the cumulative duration of labor of women in the 5^th, 50^th, and 95^th percentiles. The estimated cumulative duration of time includes a wide variation, consistent with the previously described data from the study cohort. In the target cohort duration of first stage among nulliparous are longer than in the study cohort. S2–S4 Figs illustrate the 95^th percentiles of cumulative labor duration for the target population cohort and plotted as staircase lines based on the cervical dilation observed at admission, and centimeter by centimeter until full cervical dilation. Including women with cesarean delivery in the target population cohort did not lead to any major change in pattern or trajectories for parity 1 and parity 2+ women.

Discussion

Swedish cohort vs Friedman and contemporary cohorts

There is wide variation of first stage labor progression in this low-risk population, and more rapid labor progress should not be expected until at least 5–6 centimeter of cervical dilation regardless of parity. These findings correspond to previous studies by Zhang [26] and Oladapo [23], displayed in Table 4.

Table 4. Duration of labor compared with Zhang [26] and Oladapo[23] results.

Cervical dilation	Cervical dilation	Current study	Zhang et al	Oladapo et al
3	4	0.83 (0.14–4.97)	1.8 (8.1)	2.82 (0.60–13.33)
4	5	0.89 (0.15–5.26)	1.3 (6.4)	1.72 (0.38–7.83)
5	6	0.68 (0.10–4.55)	0.8 (3.2)	1.19 (0.23–6.17)
6	7	0.48 (0.06–3.82)	0.6 (2.2)	0.66 (0.09–4.92)
7	8	0.33 (0.03–3.62)	0.5 (1.6)	0.25 (0.02–3.10)
8	9	0.24 (0.02–3.00)	0.5 (1.4)
8	10			0.87 (0.18–4.19)
9	10	0.18 (0.01–2.66)	0.5 (1.8)

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Data are reported as median hours (5^th, 95^th percentiles)

Zhang et al data reported as median hours (95^th percentile)

Interestingly, in the Swedish cohort, the median progression from one centimeter to the next was more rapid than one hour from 3 cm dilation and throughout first stage. These results differ from the results of both Zhang [26] and Oladapo [23]and is even shorter than the 1 cm per hour average cervical dilation described in the landmark publications of Friedman and others [1, 2, 5]. Results also suggest that women with the longest labors can progress slowly during the entire first stage. For example, it might take as long as 3 hours to progress from 8 to 9 cm dilation for a woman giving birth to her first child. Those whose labor durations reached or exceeded the 95^th percentile had substantially longer labor duration after 6 cm compared to Zhang’s findings [26] but our results were similar to Oladapo’s findings [23]. Findings of this analysis support previous authors’ conclusions that an “average” dilation median rate for women during the first stage of labor does not exist [22, 23, 32, 33].

Clinical management and setting

The variety of duration of first stage shown in this study and compared with the results by Zhang [26] and Oladapo [23], could reflect differences in obstetrical settings, clinical management factors and possibly, to a minor extent, differences in maternal and neonatal anthropometrics, such as or example BMI and fetal weight. Further, due to the strict inclusion criteria in this study, with 100% effacement, it could be that more women are in advanced first stage of labor when admitted compared to the women in Zhangs cohort [26]. More than 80% of the women in the Oladapo study had advanced cervical effacement (very thin cervix) [23]. The few known causal factors influencing first stage duration are maternal age, increasing BMI, posterior fetal position and higher fetal weight [34–40]. Compared to the African and American cohorts, the Swedish cohort was older, had lower BMI, lower gestational age at birth, and fetal weight was higher. Strengths and regularity of contractions have not been evaluated in any of these studies but could influence the patterns of labor.

The influence of epidural analgesia on the duration of first stage of labor remains unclear and was not evaluated in this study [41]. Our cohort had a higher rate of oxytocin (49% in nulliparous) than the two other cohorts (47% Zhang, 40% Oladapo). Oladapo’s results demonstrated slightly faster labor progression when excluding women with oxytocin, the authors emphasized the translational relevance of including women with augmentation due to the frequent use [23]. Because synthetic oxytocin use is common in Swedish maternity care, we choose to include those receiving this intervention to avoid selection bias and mirror the clinical setting.

Why is labor progression and duration important in childbirth?

One reason to reevaluate normal labor progression is to facilitate understanding of normal birth. This is critical to building maternity care systems that endorse patience when labor progress is normal and intervention only when it is maximally beneficial. This could lead to reduction of unnecessary caesarean sections. The LAPS study compared the WHO partograph with the Zhang guidelines on normal progression [42]. The hypothesis was that a more dynamic labor curve, allowing more time early in labor, before 5–6 cm, would affect the caesarean delivery rate. Result of this study showed an overall decrease in the cesarean delivery rate for all women within the LAPS study, regardless of which guideline was used. The authors suggest that the overall lower cesarean rate during the study period was related to an increased focus on labor progression, rather than the use of a new guideline [42]. The definition of prolonged labor in the intervention group was based on the traverse time in Zhangs cohort from women with the slowest labors (95^th percentile) (2.2, 1.6, 1.4, 1.8) [26]. The corresponding traverse time 95^th percentile (3.82, 3.62, 3.00, 2.66) in our study suggests even wider time intervals throughout the first stage of labor including progression at and beyond 6 centimeters of cervical dilation. Therefore, we speculate that Zhang’s definition of prolonged labor after 5–6 centimeters dilation might be too conservative in some settings.

Labor progression for all women (including cesarean delivery)

One major challenge in studies on labor progression is how to avoid potential selection bias in the cohort. To exclude women giving birth by cesarean and/or with adverse neonatal outcome might introduce selection bias. To investigate this, we created a target population cohort including women regardless of mode of delivery and regardless of neonatal outcome (S1–S3 Tables, S1–S4 Figs). In the supportive material we have presented a target population cohort of 101,730 women and our findings suggest that there are important differences between the cohorts that needs to be further explored. Interestingly, fetal posterior position was almost twice as common when women with cesarean delivery were included in the cohort. For instance, nulliparous women in this cohort had two hours longer duration at the 95^th percentile when we included those who delivered by CS vs. findings when those with CS and adverse neonatal outcome were excluded. These results correspond with findings of the LAPS Study which showed that women who delivered by intrapartum cesarean delivery had a prolonged labor duration compared with those who delivered vaginally in both study groups [43]. Future research is needed to better understand if labor duration or other factors, such as fetal malposition, may signal risk for cesarean delivery and/or adverse neonatal outcome.

Clinical implications

Strengths and limitations

There are several study strengths. First, we had access to a large cohort of more than 85,000 women contributing information on progress of labor. As women are admitted to the hospital at different stages of labor (from 3 to 6 cm cervical dilation) the large size of the cohort permits robust analysis for estimating labor durations in a wide variety of clinical scenarios, including those who were admitted to the hospital at earlier as well as more advanced labor. Furthermore, by using the unique personal identity number all information was collected prospectively in standardized antenatal obstetric and neonatal records, minimizing the potential for recall bias [44]. Selection bias is further minimized as all pregnant women in Sweden are offered free health care from pregnancy to postpartum care and more than 99% of all women attend antenatal care and give birth in a hospital. The cohort consists of approximately 25% of all births in Sweden and the unique equal health care system available for all women strengthens the external validity as this is a cohort based on the average Swedish population. While we acknowledge the limitation of describing ‘normal’ labor patterns in a sample with frequent intervention, we also believe that the inclusion of women with interventions such as amniotomy, epidural, and oxytocin augmentation strengthens the generalizability of our results to current obstetric practice. Robust consideration of the appropriate methodological approach to advancing this science that have been published during the last decade and directly informed our analysis [29, 45]. By using strict criteria (C1-C2) for inclusion in the cohort we minimized potential selection bias arising due to inclusion of women admitted to the hospital before the first stage of labor. Because the inclusion criteria included several clinically validated parameters we consider it to be a model with high precision. It has been almost a decade since Zhang presented the labor curves on an American population and a number of smaller studies have been published using the same statistical approach. This is the first cohort study based on a Swedish population and, to our knowledge, it is the labor progression study with the largest sample. The landmark research by Friedman enormously impacted labor management over the last 60 years. To refine and update our understanding of normal labor progress and labor management, more research using contemporary cohorts is necessary. Our study, using the same statistical approach as seminal researchers and analyzing a new cohort, contributes to this broader effort.

There are also limitations to this study. We excluded women with induced labors, cesarean deliveries, and pregnancies in non-vertex presentation to enable comparison to seminal findings, therefore our findings cannot be generalized to these women. Also, women are admitted to the hospital at different stages of labor, and they may differ in terms of labor progression and clinical management. It could be speculated that women who are admitted early during first stage may be exposed to more interventions (amniotomy or oxytocin) to speed up progression compared to women who are admitted later during first stage, which has not been evaluated in this study. The start of contractions among spontaneous onset labors is at home and the starting point of regular painful contractions could be prone to recall bias. Since this time point is one of several criterions we still believe it is a model of high precision. In future studies on “normal progress of labor” maternal outcomes such as postpartum hemorrhage, perineal lacerations, urinary and faecal incontinence, and negative birth experience may also be considered being included in the definition “adverse birth outcome”. Importantly, normal delivery outcomes were restricted to infant outcomes and we cannot conclude anything about the risk for adverse maternal outcomes in relation to labor duration. Finally, the supportive material in this study revealed important differences in duration between the target population cohort and the study cohort. This identifies the need to evaluate differences in progression of labor and labor duration in various cohorts to identify the threshold for true dystocia.

Conclusion

Our findings, considered in conjunction with Zhang’s [26] and Oladapo’s [23] work, indicate that greater patience with first stage labor progress is warranted and suggest the need for increased clinical and hospital policy focus on all aspects of progression in labor. Average first stage of labor progression expectations based on the traditional partograph should not be used for clinical management. This large cohort study of first stage of labor indicates that duration and progression differ substantially from the traditional partograph alert lines in defining normal progress of labor. Similar to other recent labor progress research, our results show an acceleration of cervical advancement beginning at 5–6 centimeters of dilation. Swedish women’s cervical dilation can progress both faster and significantly slower than 1 cm per hour throughout the first stage of labor and still conclude in vaginal birth with normal neonatal outcomes. These results, considered with findings of other first stage of labor progress research, signal the need for a line of inquiry aimed to revise labor dystocia definitions.

To successfully distinguish thresholds for when labor is too long for the individual woman and infant, we need to gain more knowledge on both protective factors and risk factors. Future research might be enhanced through evaluating long-term follow up on infant and maternal health in relation to labor progress and duration estimates of both the first and second stages of labor duration. Given our findings that traverse time is slower when women with cesarean delivery and adverse neonatal outcome are included in the analysis, we also recommend that future analyses consider both observations with vaginal birth and normal outcomes as well as cesarean birth and abnormal outcomes. Duration of time in labor has long been considered of central importance in distinguishing risk. Our findings in the context of similar results, demonstrate the wide variability of total first stage of labor durations and trajectories of cervical dilation among those birthing vaginally with normal neonatal outcomes. This may signal that factors other than duration of the first and second stages of labor are more critical to maternal/child risk.

Supporting information

S1 Table. Maternal, labor and fetal characteristics for target population cohort.

(DOCX)

Click here for additional data file.^{(20.5KB, docx)}

S2 Table. Duration of labor in hours from one-centimeter dilation to the next, by parity for target population cohort.

(DOCX)

Click here for additional data file.^{(14.7KB, docx)}

S3 Table. Cumulative duration of labor in hours in para 0, 1, and 2+ based on the cervical dilation at admission for target population cohort.

(DOCX)

Click here for additional data file.^{(17KB, docx)}

S1 Fig. Diagram of patient selection for target population cohort.

(TIF)

Click here for additional data file.^{(95.2KB, tif)}

S2 Fig. The 95^th percentiles of cumulative duration among nulliparous for target population cohort.

(TIF)

Click here for additional data file.^{(427KB, tif)}

S3 Fig. The 95^th percentiles of cumulative duration among parity = 1 for target population cohort.

(TIF)

Click here for additional data file.^{(430.3KB, tif)}

S4 Fig. The 95^th percentiles of cumulative duration among parity = 2+ for target population cohort.

(TIF)

Click here for additional data file.^{(434.5KB, tif)}

Data Availability

The Stockholm-Gotland Obstetric Cohort was used for this study. Information in the database was retrived from the medical record system Obstetrix. The regional ethical committee at Karolinska Institutet, Stockholm, Sweden approved the study protocol (No 2009/275-31, 2012/365-32, 2013/792-32, 2014/177-32, 2014/962-32). The database is stored in the Unit of Clinical epidemiology at Karolinska Institutet Stockholm, Sweden. Public datasharing from this data base is not permitted. Any questions regarding public access to the data is handled by Unit of Clinical epidemiology. Department of Medicine, Karolinska Institutet, Professor sven.cnattingius@ki.se@ki.se.

Funding Statement

This study was supported by grants provided by the Stockholm County Council (ALF project 2017-01000 MA) https://forskningsstod.vmi.se/Ansokan/start.asp, and Swedish Research Council for Health, Working Life and Welfare (STYA-2017/0003) (MA, LL) https://www.government.se/government-agencies/swedish-research-council-for-health-working-life--forskningsradet-for-arbetsliv-halsa-och-valfard-forte/ The funding sources had no role in study design, collection of data, preparation of the manuscript, analysis or interpretation of data, nor in decision to submit the article for publication.

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PLoS One. doi: 10.1371/journal.pone.0239724.r001

Decision Letter 0

Roger C Young

29 May 2020

PONE-D-20-06618

First stage progression in women with spontaneous onset of labor: A large population-based cohort study

PLOS ONE

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Reviewer #1: Thank you for the opportunity to review this excellent and significant manuscript. It adds another very large analysis to the obstetrical literature from another geographical region, describing the relationship between dilation and time using 3 different techniques. It confirms what all other recent studies have shown namely that, on average, dilation proceeds in a near exponential fashion not the sigmoid shape depicted in the traditional Freidman curves. In addition, the authors confirm the very wide variation in dilation rates and clearly state the problem that this large variation creates when one tries to use an “average” curve to manage labor. This conclusion is very important because generations of Obstetricians have been taught to evaluate labor based on a presumed average curve with relatively narrow variation in the rates of expected progress. Although there is now wide acceptance that the dilation curve is not sigmoid in shape, nor linear after 3 cm, there is less appreciation that there is no substantial clustering (central tendency) of patients around an “average”. That is, while it is always possible to contruct a mathematical average, few patients actually follow this mathematical average. Bravo for stating this so explicitly and repeatedly throughout this paper.

In addition, results indicated that NTSV Swedish women progressed faster in early first stage compared to findings the in USA based publications (Zhang 2010) and faster compared to 2 subsaharan countries women (Oladapo 2018). In late first stage, Swedish women progressed more slowly than the rates reported for USA women and similar to those reported for the Ugandan and Nigerian women.

There are a few points worth mentioning in the discussion.

Developing a model with precision:

The general problem of modeling a process (in this case, cervical dilation) with precision: The authors have demonstrated excessively wide variation when the model is based on only parity and time. It would be useful to discuss the known causes of poor modeling precision such as imprecise measurements and unmeasured influential factors. The observation that model precision improved when the models are restricted to higher and higher admission dilations suggest that some unmeasured factors may become more homogeneous with advancing labor. Cervical effacement, contraction strength and frequency, epidural use and censoring due to intrapartum cesarean are candidates.

Entry point and the effect of incomplete effacement:

Re comparisons of traverse time at low dilations. You noted a faster median time to advance from 3 to 4 cm in the Swedish women 0.83h (95th 4.97) compared to USA 1.8h( 95th 8.1) and compared to 2 subSaharn African countries 2.8h (95th 13.3) I presume these are Uganda and Nigerian women based on other more detailed publications by Oladapo et al. The inclusion criteria in this Swedish study were women with singleton, term, vertex presentations and spontaneous onset of labor and vaginal birth. Exclusion for < 3 examinations, missing exam at 10 cm, Apgar 5 min <7, or any of diagnosis related to HIE or meconium aspiration.

The onset of active labor was defined as the presence of regular painful contractions and a well effaced cervix and a dilation of 3cm or rupture of membranes with a dilation of 3 cm.

Zhang et al 2010 included NTSV patients with spontaneous onset of labor without a requirement for a specific dilation (10% had a dilation of 1 cm or less) or a requirement for a specific effacement ( 10% had an admission effacement of 60% or less.

Please present the comparative statistics on the admission examination findings because the state of the cervix on admission has a large influence on rates of dilation in the beginning.

Censoring effect of cesarean:

The NTSV cesarean rates in Sweden are much lower than in the USA and perhaps more comparable to that in the Oladapo studies.

In the LAPS study, Swedish CS rates in NTSV in 2014 were approximately 9.5% before the intervention.

In the USA CS rates for NTSV were approximately 27.5% in 2007 (Zhang et al 2010, women mostly from 2005- 7)

Please comment on how the removal of more patients for labor disorders could affect the dilation rates in the residual population used for modeling. I agree that maternal and fetal anthropomorphic differences can account for some differences but this censoring effect could be present as well and bears mentioning.

Recommendations for clinical practice drawn from a study of “normal” labors.

You have commented very carefully on how labor curves and your findings could help direct management. I think it would be very useful to remind the reader that any study that intentionally excludes all abnormal outcomes cannot determine the safety of a particular intervention threshold.

Reviewer #2: This paper used a large electronic obstetric database to examine the labor pattern and duration of first stage of labor. The analysis was well done and the paper clearly written. The findings are reasonable and potentially useful clinically. To improve this paper, several issues need more attention by the authors:

1. What was the overall CS rate in this study population? What was the proportion of prelabor vs. intrapartum CS? Given that the overall CS rate in Sweden (18%?) is low and intrapartum CS rate is even lower, the observed longer duration of labor at the 95th percentile than that in the Zhang's data appears reasonable as the U.S. overall CS rate is over 30%. This could be one of the explanations for the difference between the studies.

2. Ideally, the following women should also be excluded from the study: women with a scarred uterus, postpartum hemorrhage or III or IV degree perineal laceration. This may also address the issue stated on Line 180-181 in Strength and limitation.

3. The authors defined "the first stage of labor" and "onset of active phase" but in the paper, they never really showed any results that were associated with these two definitions. If it is true, then I'd suggest not to mention them as these definitions are still controvercial.

4. The median cervical dilation at admission was 5 cm. Thus, the admission seems a little late, comparing to other databases. What was the median effacement?

5. The number of vaginal exams tended to be at low side. The authors may want to discuss the impact of fewer data points on the results.

6. Women who were admitted at different phases of labor may differ in terms of labor progression. How that may have affected the results? Some discussion is needed.

**********

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PLoS One. 2020 Sep 25;15(9):e0239724. doi: 10.1371/journal.pone.0239724.r002

Author response to Decision Letter 0

3 Aug 2020

Dear Editor

Thank you for your thoughtful critique of our manuscript ‘First stage progression in women with spontaneous onset of labor: A large population-based cohort study’. We have made several changes to the manuscript in response to your critique, and we feel that these changes strengthen the manuscript.

Of note, we have given the censoring effect of CS extra attention as you and the two reviewers requested. The scope of this study included normal labors for comparison to seminal findings. However the question of selection bias by excluding cesarean delivery (and adverse neonatal outcome) is a problem; we agree with the reviewers comments and have adressed them. To address the question of selection bias and censoring effect of excluding CS and births with adverse neonatal outcomes we have now added additonal analyses on labor duration in a target population cohort including women delivered by CS and adverse neonatal outcomes. Results of these additional analyses have been added to supplemental materials.

Please see the questions and answers (in italics) together with line numberings (in red) corresponding to the changes made in the tracked changes document.

Reviewer 1#

1. Developing a model with precision

We consider the large cohort that we used for this analysis to be a major strength related to this concern. The size of the sample provides enough obeservations to enable robust point estimates even at smaller dilation. We also consider the fact of the strict inclusion criteria- e.g., only including women with painful regular contactions, fully effaced cervix, and a notation of cervical dilation- as a strength on this concern as these increase the likelihood that we only included women who are in active labor and not in the latent phase. This has been clarified in the Strengths and Limitations section (lines 461-468) (lines 479-486).

This approach differs from the studies by Zhang and Oladapo and these differences are now clarified in the Discussion (lines 364-367).

2. Entry point and the effect of incomplete effacement

Re comparisons of traverse time at low dilations. You noted a faster median time to advance from 3 to 4 cm in the Swedish women 0.83h (95th 4.97) compared to USA 1.8h( 95th 8.1) and compared to 2 Sub Saharian African countries 2.8h (95th 13.3) I presume these are Uganda and Nigerian women based on other more detailed publications by Oladapo et al. The inclusion criteria in this Swedish study were women with singleton, term, vertex presentations and spontaneous onset of labor and vaginal birth. Exclusion for < 3 examinations, missing exam at 10 cm, Apgar 5 min <7, or any of diagnosis related to HIE or meconium aspiration.

The onset of active labor was defined as the presence of regular painful contractions and a well effaced cervix and a dilation of 3cm or rupture of membranes with a dilation of 3 cm.

Please present the comparative statistics on the admission examination findings because the state of the cervix on admission has a large influence on rates of dilation in the beginning.

Cervical effacement, one of the criterion in this study, was 100% (or almost) effacement. We have now clarified this in the defintion on starting point for first stage in the method section (lines 155-170). We have also added information regarding self-report issues (contractions) and clinical examination in both the Methods section and in Strengths and Limitations (lines 155-170 ) (lines 479-486).

3. Censoring

Thank you for this important critque. To explore the censoring effect of cesarean delivery we conducted the same analyses in the whole population (target population), including all intrapartum CS as well as adverese neonatal outcomes. (lines 172-180) We have added results in supportive material. We have also expanded the discussion to comment these findings. (lines 309-326) (lines 410-426) (lines 511-512)

4. Safety

We agree. We have now updated and clarified the limitations of excluding abnormal outcomes and reminded the reader about this limitation in the Strengths and Limitations sections. (lines 486-489) (lines 511-514)

Reviewer # 2:

1. What was the overall CS rate in this study population?

Cesarean delivery 11.4 % for nulliparous, 2.1% for parity 1 and 1, 6% for parity 2+. ( S.Table 1)

2.What was the proportion of prelabor vs. intrapartum CS?

Those with prelabor cesarean deliveries were not included in this study. The intrapartum cesarean delivery rates within this cohort are 11.4 % for nulliparous, 2.1 % for parity 1, and 1.6% for parity 2+.( S.Table 1)

3. Given that the overall CS rate in Sweden (18%?) is low and intrapartum CS rate is even lower, the observed longer duration of labor at the 95th percentile than that in the Zhang's data appears reasonable as the U.S. overall CS rate is over 30%. This could be one of the explanations for the difference between the studies.

We agree that this variation in CS rates is important and should be further addressed indicate. To our discussion under the headline “Why is labor progression..”. (lines 389-409), we have now added statistical analysis for a target population cohort to further fully describe the effects of labor duration of including/excluding women due to cesarean delivery and adverse neonatal outcomes. (lines 172-182) (lines 313-330) (lines 410-426) (lines 511-514)

4. Ideally, the following women should also be excluded from the study: women with a scarred uterus, postpartum hemorrhage or III or IV degree perineal laceration. This may also address the issue stated on Line 180-181 in Strength and limitation.

Women with scarred uterus (previous cesarean) are already excluded in original manuscript in this study cohort. (Fig 1, line 133). We agree that women with postpartum hemorrhage or III or IV degree perineal laceration should be excluded when evaluating normal labors, however for comparison to seminal findings we decided to keep the cohort as identical as possible to the Zhang and Oladapo cohorts. For future research on labor progression, ideally women with postpartum hemorrhage or 3,4-degree perineal laceration should be excluded - we agree with you on this point. This is now stated in Strengths and limitations. (lines 486-492)

5. The authors defined "the first stage of labor" and "onset of active phase" but in the paper, they never really showed any results that were associated with these two definitions. If it is true, then I'd suggest not to mention them as these definitions are still controvercial.

We have now changed the phrasing “onset of active phase” to ‘starting point for first stage of labor’, which we agree is a better definition. Furthermore, we have now clarified the definition of starting point for duration of first stage of labor in this study in the Methods section. (lines 155-170).

6. The median cervical dilation at admission was 5 cm. Thus, the admission seems a little late, comparing to other databases. What was the median effacement?

From our review of the literature, we note that the median cervical dilation at admission differs in different cohorts. This likely reflects how care is organized in different countries or potentially differences in women’s expectations of when to seek hospital admission for birth. Our study is based on prospectively collected data by certified midwives, and we consider the data to be of high precision.

The criteria for inclusion in this study was complete or nearly 100 % effacement meaning that there was no median to report. (lines 155-170)

7. The number of vaginal exams tended to be at low side. The authors may want to discuss the impact of fewer data points on the results.

We have discussed the question of precision (fewer data points) in the original manuscript under strenghts and limitations. (lines 461-468) (lines 479-486). (lines 443-448) (Please see answer number 1 rewiver 1). Due to the size of the cohort as well as the large portion of the sample with estimates for traverse times, we believe that our estimates on this point are robust. (Table 2, Please see numbers of women included for every cm dilation). The number of vaginal exams [median 4 (2,7)] reflects how midwives and clinicans work in the study setting. These clinical practices are similar to the number of vaginal exams found in prior research: 3 (2,5) (Oladapo), 5 (1, 9) (Zhang).

8. Women who were admitted at different phases of labor may differ in terms of labor progression. How that may have affected the results? Some discussion is needed.

We aimed to avoid including women admitted too early in labor ( possibly in the “latent phase”), and we have added additional information to address the above question under strengths and limitations. (lines 461-464) Also, as the reviewer helpfully noted in question 5, the definiton of “active phase” is still controversial. We have therefore removed this expression from the manuscript. ( Please see answer number 5 rewiver 2)

However, it could be speculated that women admitted early vs. late during first stage differ in terms of labor progression as shown in cumulative distributions. Thus we agree with you on this point. The impact of more/ less interventions in early vs late admission was not evaluated in this study. This is now more clearly stated in strengths and limitations. (lines 479-486)

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PLoS One. doi: 10.1371/journal.pone.0239724.r003

Decision Letter 1

Roger C Young

4 Sep 2020

PONE-D-20-06618R1

First stage progression in women with spontaneous onset of labor: A large population-based cohort study

PLOS ONE

Dear Dr. Lundborg,

==============================

Please see my comments below.

==============================

Please submit your revised manuscript by Oct 19 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

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We look forward to receiving your revised manuscript.

Kind regards,

Roger C. Young

Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

This revision is significantly improved. I would like you to consider the following suggestions. To emphasize, these are suggestions only and I leave open the opportunity for you to not include them in the final version if you so choose.

Abstract:

Results:

1. ,[the rate of] cervical dilation accelerates ...

2. Among nulliparous women, the median time [found in our population] was faster [than] their counterparts...

3. Among nulliparous and multiparous women [our data] suggest that ... [, however, ] traverse time at and beyond.....is [slower] than 1 cm per hour.

Conclusions:

1. ...widely and [labors experiencing a prolonged first stage] can still...

2. 1 cm [per hour cervical dilation rate for the first stage of labor] may not be [universally] meaninful.

3. ... differences in progression[for women] in different populations.

4. [For] prolonged labor progression [to be more clinically meaningful, the] association with adverse birth outcomes needs to be further investigated [in specific populations].

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #2: Yes

**********

6. Review Comments to the Author

Reviewer #2: (No Response)

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

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Reviewer #2: No

PLoS One. 2020 Sep 25;15(9):e0239724. doi: 10.1371/journal.pone.0239724.r004

Author response to Decision Letter 1

10 Sep 2020

Thank you for your response to our resubmission on the manuscript ‘First stage progression in women with spontaneous onset of labor: A large population-based cohort study’.

We have made final minor changes in the abstract, only according to your thoughtful last suggestions. No other changes have been made in the manuscript.

Thank you for your attention to our paper.

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PLoS One. doi: 10.1371/journal.pone.0239724.r005

Decision Letter 2

Roger C Young

14 Sep 2020

First stage progression in women with spontaneous onset of labor: A large population-based cohort study

PONE-D-20-06618R2

Dear Dr. Lundborg,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Roger C. Young

Academic Editor

PLOS ONE

PLoS One. doi: 10.1371/journal.pone.0239724.r006

Acceptance letter

Roger C Young

16 Sep 2020

PONE-D-20-06618R2

First stage progression in women with spontaneous onset of labor: A large population-based cohort study

Dear Dr. Lundborg:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Roger C. Young

Academic Editor

PLOS ONE

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Table. Maternal, labor and fetal characteristics for target population cohort.

(DOCX)

Click here for additional data file.^{(20.5KB, docx)}

S2 Table. Duration of labor in hours from one-centimeter dilation to the next, by parity for target population cohort.

(DOCX)

Click here for additional data file.^{(14.7KB, docx)}

S3 Table. Cumulative duration of labor in hours in para 0, 1, and 2+ based on the cervical dilation at admission for target population cohort.

(DOCX)

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S1 Fig. Diagram of patient selection for target population cohort.

(TIF)

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S2 Fig. The 95^th percentiles of cumulative duration among nulliparous for target population cohort.

(TIF)

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S3 Fig. The 95^th percentiles of cumulative duration among parity = 1 for target population cohort.

(TIF)

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S4 Fig. The 95^th percentiles of cumulative duration among parity = 2+ for target population cohort.

(TIF)

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Submitted filename: Firststageprogression.Readytosend.LettertoEditor..docx

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Data Availability Statement

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PERMALINK

First stage progression in women with spontaneous onset of labor: A large population-based cohort study

Louise Lundborg

Katarina Åberg

Anna Sandström

Andrea Discacciati

Ellen L Tilden

Olof Stephansson

Mia Ahlberg

Roles

Abstract

Objective

Design

Population

Main outcome measures

Results

Conclusions

Introduction

Material and methods

Fig 1. Diagram of patient selection for study cohort.

Statistical analysis

Table 3. Cumulative duration of labor in hours in para 0, 1, and 2+ based on the cervical dilation at admission.

Fig 2. Labor curve for a random sample of numerous women based on percentiles 5-95th for nulliparous.

Fig 4. Labor curve for a random sample of numerous women based on percentiles 5-95th for parity = 2+.

Fig 3. Labor curve for a random sample of numerous women based on percentiles 5-95th for parity = 1.

Results

Table 1. Baseline characteristics of the study population by parity.

Table 2. Duration of labor in hours from one-centimeter dilation to the next, by parity.

Fig 5. The 95th percentiles of cumulative duration among nulliparous.

Fig 7. The 95th percentiles of cumulative duration among parity = 2.

Fig 6. The 95th percentiles of cumulative duration among parity = 1.

Discussion

Swedish cohort vs Friedman and contemporary cohorts

Table 4. Duration of labor compared with Zhang [26] and Oladapo[23] results.

Clinical management and setting

Why is labor progression and duration important in childbirth?

Labor progression for all women (including cesarean delivery)

Clinical implications

Strengths and limitations

Conclusion

Supporting information

Data Availability

Funding Statement

References

Decision Letter 0

Roger C Young

Roles

Author response to Decision Letter 0

Decision Letter 1

Roger C Young

Roles

Author response to Decision Letter 1

Decision Letter 2

Roger C Young

Roles

Acceptance letter

Roger C Young

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

Similar articles

Cited by other articles

Links to NCBI Databases

Fig 2. Labor curve for a random sample of numerous women based on percentiles 5-95^th for nulliparous.

Fig 4. Labor curve for a random sample of numerous women based on percentiles 5-95^th for parity = 2+.

Fig 3. Labor curve for a random sample of numerous women based on percentiles 5-95^th for parity = 1.

Fig 5. The 95^th percentiles of cumulative duration among nulliparous.

Fig 7. The 95^th percentiles of cumulative duration among parity = 2.

Fig 6. The 95^th percentiles of cumulative duration among parity = 1.