Maternal and perinatal outcomes of prolonged second stage of labour: a historical cohort study of over 51,000 women

doi:10.21203/rs.3.rs-2002850/v1

Background

Prolonged second stage of labour has been associated with adverse maternal and perinatal outcomes. The maximum length of the second stage from full dilatation to birth of the baby remains controversial. Our objective was to determine whether extending second stage of labour was associated with adverse maternal and perinatal outcomes.

Methods

A retrospective cohort study was conducted using routinely collected hospital data from 51,689 births in Aberdeen Maternity Hospital between 2000 and 2016. The hospital followed the local guidance of allowing second stage of labour to extend by an hour compared to national guidelines since 2008 (nulliparous and parous). The increasing duration of second stage of labour was the exposure. Baseline characteristics, maternal and perinatal outcomes were compared between women who had a second stage labour of (a) ≤ 3 hours and (b) > 3 hours duration for nulliparous women; and (a) ≤ 2 hours or (b)> 2 hours for parous women using univariate analysis. The following were then adjusted for: age, BMI, parity, smoking status, deprivation category, induced birth, epidural, oxytocin, gestational age, baby birthweight and mode of birth. The length of second stage was entered as a continuous variable

Results
Each hourly increase in the second stage of labour was associated with an increased risk of tears (aOR 1.52 95% CI 1.49-1.56), having an episiotomy (aOR 2.10 95% CI 2.06-2.14) and postpartum haemorrhage (aOR 1.55 95% CI 1.53-1.58). The rates of caesarean and forceps delivery also increased threefold when second stage duration increased (aOR 3.38 95% CI 3.26-3.50, aOR 3.18 95% CI 3.11-3.26, respectively.) No statistically significant adverse perinatal outcomes were found on multivariate analysis.

Conclusions

As the duration of second stage of labour increased, the risk of tears, episiotomies and PPH increases significantly. Women were 3 times more likely to have a forceps or caesarean birth. No association was found between adverse perinatal outcomes and the duration of second stage of labour in this study.

Second stage

Birth

Prolonged labour

The second stage of labour varies in duration from minutes to many hours. Prolonged second stage, particularly where labour is obstructed, has been associated with complications such as postpartum haemorrhage (PPH) and in severe cases obstetric fistula. However, the optimal limit on the duration of second stage, in the absence of fetal concerns or maternal exhaustion, after which an intervention to expedite the birth should be recommended is not known.

A decision to intervene to limit the second stage of labour requires a balance of the risks and benefits compared to awaiting spontaneous birth. Operative vaginal birth risks include Obstetric Anal Sphincter Injury (OASI) and rarely nerve or bony injury for the newborn [1]. Second stage caesarean birth also presents a substantial risk of maternal trauma, haemorrhage and risk of trauma to the infant [2], as well as the risks for subsequent pregnancies. Both interventions are also linked to maternal post-traumatic stress symptoms [3].

While the evidence is limited, the 2017 National Institute for Health and Care Excellence (NICE) has recommended offering intervention after 3 hours of active second stage for nulliparous and 2 hours for parous women [4]. Prior to this, a 2006 systematic review [5] demonstrated a lack of reliable evidence that the duration of second stage was linked to adverse maternal or perinatal outcomes. Study limitations at the time included broad categorisations of second stage duration (i.e < 3 hours vs. > 3 hours) and lack of data on potential confounding factors. However, the 2006 review led to changes in clinical guidance in Aberdeen (NHS Grampian) which involved offering intervention after 4 hours of second stage for nulliparous and 3 hours for parous women, taking effect in 2008. The Aberdeen Maternity and Neonatal Databank (AMND) includes detailed labour stage duration data along with multiple covariates and captures sufficient cases exceeding 4 hours in second stage to enable this detailed study of prolonged second stage and the associated risks. The AMND had the unique opportunity to analyse prolonged second stage due to this change in local guidance.

2.1 Design

This study looks at the relationship between the duration of second stage of labour and adverse outcomes for mothers and newborns. The findings of this study are key in providing women and clinicians with information to support informed decisions on whether and when to intervene in prolonged second stage of labour with an increased awareness of the heightened risk.

A population-based retrospective cohort study using routinely collected anonymised data was conducted to determine whether increasing the duration of second stage of labour was associated with a corresponding increase in the risks of morbidities for mother and newborn. The population studied included all singleton births at or beyond 37 weeks gestation reaching second stage of labour that occurred between 2000 and 2016 inclusive.

This study data source was the AMND [6] which includes routinely collected data for all pregnancies and babies where birth occurred in Aberdeen City and District since 1950. This means AMND captures births prior to a change in local policy on second stage management before 2008 (length of labour similar to the rest of the country) in addition to those with a significantly prolonged second stage of labour (predominantly after 2008).

Study approval was gained from the AMND steering committee, which has ethical approval from the North of Scotland Research Ethics Service for studies which utilise anonymised unlinked data (19/NS/0079). The data was stored on a secure password protected University server. Regular quality assurance checks of AMND data are carried out [6].

Pregnancies were excluded if there was a known intrauterine death as data did not allow for differentiation between antepartum and intrapartum stillbirth. Furthermore, labour and birth outcomes are likely to be significantly different for stillborn babies.

The services captured by the databank follows the national guidelines on fetal monitoring by using intermittent auscultation in low-risk women and higher risk women would receive CTG and labour ward care. When the second stage of labour became prolonged the monitoring would switch from intermittent auscultation to CTG.

2.2 Data management

The data was cleaned by removing cases with inconceivable values for the following characteristics and outcomes: duration of second stage of labour, baby birthweight, cord pH and length of stay. A complete case analysis was performed.

Maternal outcome data included mode of birth, episiotomy, OASI, and PPH. Perinatal outcome data included Apgar score<7 at 5 minutes, cord pH and admission to Neonatal intensive care unit (NICU). Additional variables obtained included the duration of second stage of labour (exposure), parity and clinical and demographic characteristics that could be potential confounders (Table 1, 2 and Appendix 1).

2.3 Data analysis:

Potential confounders were identified by comparing the characteristics of those nulliparous women who had a second stage of labour lasting <3 versus >3 hours and parous <2 versus >2 hours. These intervals were coded as 0-119 minutes for < 2 hours and 120-maximum (8 hours) for >2 hours, and the equivalent methodology for <3 (0-179 minutes) and >3 hours (120-480 minutes). The outcomes were also initially compared according to these intervals for the nulliparous and parous cohorts separately. Statistical analysis was carried out using Chi-squared test, independent t-test and one way ANOVA according to variable type. Only variables that were found to be significant (p<0.05) were included in the multivariate analysis. The characteristics were also evaluated as they changed over each hour increment (at a maximum of 8 hours), see Appendix 2 and 3.

The models treated duration of second stage of labour as a continuous variable measured in hours and combined the nulliparous and parous cohorts for the main analysis (Table 3). Outcomes included were OASI, episiotomy, PPH, mode of birth and admission to NICU. PPH was defined as >500ml for spontaneous vaginal delivery (SVD) and >1000ml for caesarean section [7]. Cord pH was not included in the models due to high volume of missing data since it is measured only when clinically indicated.

The following models were used for the analysis: binary logistic regression for binary outcomes and multinomial regression for categorical variables.

The 2000-2016 cohort included 51689 women reaching the second stage of labour after removing the 218 cases with inconceivable values and 49 cases due to known intrauterine death. In total 25302 women were nulliparous and 26387 were parous (Appendix 4). Among mothers recorded, 87% delivered before 3 hours of second stage (97% among parous women and 77% among nulliparous women). There were 1409 instances of second stage of labour that exceeded 5 hours. There were 1818 missing cases from the original database (3.4%).

Several characteristics significantly differed between those delivering before 2 or 3 hours compared to those with prolonged labour. These characteristics were age, BMI, patient’s smoking status, deprivation category [8], type of labour, epidural, oxytocin use, gestational age and baby birthweight (see Tables 1 and 2). As a result, all of these were included as potential confounders in the multivariate analysis, alongside mode of birth.

Table 1 – Characteristics and outcomes between <3 versus ≥3 hours 2^nd stage of labour (nulliparous women)

		< 3 hours		≥3 hours		P-value
Characteristics		n/x̅/M^a	%/SD/IQR^b	n/x̅M	%/SD/IQR
Age ( years)		27	(6)	29	(5)	<0.01
BMI^c		699	(3.8%)	147	(2.5%)	<0.01
		10565	(56.7%)	3205	(55.5%)
		4838	(26.0%)	1604	(27.8%)
		2526	(13.6%)	815	(14.1%)
Patient’s smoking status	Non-smoker	15575	(82.1%)	5351	(90.8%)	<0.01
	Smoker	3403	(17.9%)	543	(9.2%)
Deprivation category	1	3564	(19.1%)	1287	(22.5%)	<0.01
	2	5298	(28.3%)	1725	(30.1%)
	3	3295	(17.6%)	1012	(17.7%)
	4	3538	(18.9%)	1031	(18.0%)
	5	1050	(5.6%)	264	(4.6%)
	6	1960	(10.5%)	407	(7.1%)
Preeclampsia and other hypertensive disease	None	16362	(84.5%)	4827	(81.1%)	<0.01
	Pre-/eclampsia	907	(4.7%)	320	(5.4%)
	Others forms	2090	(10.8%)	803	(13.5%)
Type of labour	Spontaneous	13221	(68.3%)	3920	(65.9%)	<0.01
	Induced	6138	(31.7%)	2030	(34.1%)
Epidural	Yes	4948	(25.6%)	3005	(50.5%)	<0.01
	No	14411	(74.4%)	2945	(49.5%)
Oxytocin	Yes	3068	(15.8%)	1120	(18.8%)	<0.01
	No	16291	(84.2%)	4830	(81.2%)
Antepartum haemorrhage	None	16947	(87.5%)	5267	(88.5%)	0.07
	Abruption	48	(0.2%)	5	(0.1%)
	Placenta previa	0	(0.0%)	1	(0.0%)
	Unspecified	2364	(12.2%)	677	(11.4%)
Gestational age	37	1032	(5.3%)	217	(3.6%)	<0.01
	38	2133	(11.0%)	510	(8.6%)
	39	4202	(21.7%)	1130	(19.0%)
	40	6263	(32.4%)	1984	(33.3%)
	41	5079	(26.2%)	1777	(29.9%)
	42	650	(3.4%)	332	(5.6%)
Baby birthweight		3366	(454)	3561	(432)	<0.01
Outcomes
OASI^d		1079	(5.6%)	603	(10.1%)	<0.01
Episiotomy		5565	(28.7%)	3100	(52.1%)	<0.01
Mode of birth	SVD	13282	(80.1%)	1209	(23.3%)	<0.01
	Forceps	2800	(16.9%)	3182	(61.4%)
	Assisted breech	19	(0.1%)	0	(0.0%)
	Caesarean	474	(2.9%)	792	(15.3%)
PPH^e		3801	(19.6%)	2480	(41.7%)	<0.01
Admission to NICU^f		2013	(10.4%)	641	(10.5%)	0.43
APGAR^g<7 at 5 minutes		204	(1.1%)	60	(1.0%)	0.75
Cord pH		2792	(7)	1218	(7)	<0.01

^a n/x̅/M, count/mean/median/

^bThe values in brackets represents the percentage of the characteristic/outcome at that time interval. There are the exceptions of age, baby birthweight, and cord pH which shows their mean accompanied by the standard deviation in brackets and length of stay which has its median accompanied by the interquartile range.

Statistically significant p values are shown as bold

^cBody mass index

^dObstetric anal sphincter injury

^ePostpartum haemorrhage

^fNeonatal intensive care unit

^gAppearance, Pulse, Grimace, Activity, and Respiration

Table 2 - Characteristics and outcomes between <3 versus ≥3 hours 2^nd stage of labour (parous women)

		< 2 hours		≥ 2 hours		P-value
Characteristics		n	%/SD/IQR^ab	n	%/SD/IQR^ab
Age		31	(5)	32	(5)	<0.01
BMI^c	Underweight	526	(2.1%)	9	(1.1%)
	Healthy weight	12264	(49.7%)	410	(49.5%)	0.88
	Overweight	7271	(29.5%)	277	(33.5%)
	Obese	4607	(18.7%)	132	(15.9%)
Patient’s smoking status	Non-smoker	19412	(81.1%)	1688	(88.8%)	<0.01
	Smoker	4525	(18.9%)	213	(11.2%)
Deprivation category	1	5515	(23.4%)	475	(25.7%)	<0.01
	2	6783	(28.7%)	545	(29.5%)
	3	3768	(16.0%)	340	(18.4%)
	4	3854	(16.3%)	277	(15.0%)
	5	1134	(4.8%)	81	(4.4%)
	6	2551	(10.8%)	131	(7.1%)
Preeclampsia and other hypertensive disease	None	22635	(92.6%)	1732	(89.3%)	<0.01
	Pre-/eclampsia	407	(1.7%)	47	(8.3%)
	Others forms	1403	(5.7%)	161	(2.4%)
Type of labour	Spontaneous	17863	(73.1%)	1309	(67.5%)	<0.01
	Induced	6582	(26.9%)	631	(32.5%)
Epidural	Yes	1848	(7.6%)	1029	(53.0%)	<0.01
	No	22597	(92.4%)	911	(47.0%)
Oxytocin	Yes	1611	(6.6%)	183	(9.4%)	<0.01
	No	22834	(93.4%)	1757	(90.6%)
Antepartum haemorrhage	None	22088	(90.4%)	1743	(89.8%)	0.69
	Abruption	60	(0.2%)	7	(0.4%)
	Placenta previa	2	(0.0%)	0	(0.0%)
	Unspecified	2295	(9.4%)	190	(9.8%)
Gestational age	37	1274	(5.0%)	32	(3.7%)	<0.01
	38	2978	(11.7%)	84	(9.8%)
	39	6068	(23.8%)	190	(22.1%)
	40	8790	(34.4%)	282	(32.9%)
	41	5959	(23.3%)	246	(28.7%)
	42	458	(1.8%)	24	(2.8%)
Baby birthweight		3529	(480)	3678	(475)	0.66
Outcomes
OASI^d		396	(1.6%)	43	(5.0%)	<0.01
Episiotomy		1881	(7.4%)	399	(46.5%)	<0.01
Mode of birth	SVD	23658	(96.1%)	202	(27.1%)	<0.01
	Forceps	704	(2.9%)	433	(58.0%)
	Assisted breech	73	(0.3%)	0	(0.0%)
	Caesarean	181	(0.7%)	111	(14.9%)
PPH^e		2551	(10.0%)	306	(35.7%)	<0.01
Admission to NICU^f		2047	(8.0%)	94	(11.0%)	<0.01
APGAR<7^g at 5 minutes		195	(0.8%)	11	(1.3%)	0.09
Cord pH		949	(7)	130	(7)	0.53

^a n/x̅/M, count/mean/median/

^bThe values in brackets represents the percentage of the characteristic/outcome at that time interval. There are the exceptions of age, baby birthweight, and cord pH which shows their mean accompanied by the standard deviation in brackets and length of stay which has its median accompanied by the interquartile range.Statistically significant p-values are shown as bold

^cBody mass index

^dObstetric anal sphincter injury

^ePostpartum haemorrhage

^fNeonatal intensive care unit

^gAppearance, Pulse, Grimace, Activity, and Respiration

3.1 Maternal outcomes

In the nulliparous cohort, OASI increased from 5.6% to 10.1% after 3 hours. While parous mothers saw OASI go from 1.6% to 5.0% after 2 hours (see Tables 1 and 2). The Odds Ratio (OR) for OASI was significant for both the unadjusted (OR 1.52 95% CI 1.49-1.56) and the adjusted model (aOR 1.08 95% CI 1.04-1.12), see Table 3.

Table 3 – Unadjusted and adjusted Odds ratios of adverse maternal and neonatal outcomes for hourly increase in the duration of the second stage of labour

		Unadjusted Model		Adjusted Model^a
		Odds Ratio	95% CI	Odds Ratio	95% CI
Maternal outcomes
OASI		1.52	(1.49-1.56)	1.08	(1.04-1.12)
Episiotomy		2.10	(2.06-2.14)	1.24	(1.21-1.27)
Mode of birth	SVD^b	1.00		1.00
	Forceps	3.18	(3.11-3.26)	2.44	(2.38-2.51)
	Caesarean	3.38	(3.26-3.50)	2.60	(2.50-2.70)
PPH		1.55	(1.53-1.58)	1.27	(1.25-1.30)
Perinatal outcomes
Admission to NICU		1.06	(1.04-1.08)	0.96	(0.93-0.98)

^a adjusted for parity, age, BMI, smoking status, deprivation category, spontaneous/induced labour, epidural, oxytocin use, gestational age and baby birthweight.

^bSVD = spontaneous vaginal birth, is the reference category.

Statistically significant odds ratios are shown as bold.

The chance of episiotomy use significantly increased when the second stage of labour was prolonged (see Tables 1 and 2). Episiotomies increased from 28.7% to 52.1% after 3 hours in the nulliparous cohort and went from 7.4% to 46.5% after 2 hours in the nulliparous cohort. The models demonstrated a significant odds ratio (OR 2.10 95% CI 2.06-2.14 and aOR 1.24 95% CI 1.21-127). The risk of episiotomy increased by 10% for every hour that the second stage of labour lasted, see Table 3.

In the context of the mode of birth, as the second stage of labour duration increased, SVDs became less likely while caesarean and forceps births increased. For example, in the parous cohort forceps births went from 2.9% to 58.0% after 2 hours and caesarean sections went from 0.7% to 14.9%. The models (Table 3) indicated significant ORs for forceps in the unadjusted (OR 3.18 95% CI 3.11-3.26) and the adjusted (aOR 2.44 95% CI 2.38-2.51) models. The association was also significant for caesarean sections (OR 3.38 95% CI 3.26-3.50 and aOR 2.60 95% CI 2.50-2.70).

The risk of PPH rose significantly as duration of second stage of labour extended, from 19.6% to 41.7% after 3 hours in the nulliparous cohort and 10.0% to 35.7% after 2 hours in the parous cohort (see Tables 1 and 2). This was also indicated by the significant ORs (in Table 3) (OR 1.55 95% CI 1.53-1.58 and aOR 1.27 95% CI 1.25-1.30).

3.2 Perinatal Outcomes

A significant association between the duration of second stage of labour and adverse perinatal outcomes was not identified. Admission to NICU was the only significantly perinatal outcome to increase in the parous cohort after 2 hours from 8.0% to 11.0% (p<0.01) and further supported by the unadjusted ORs (OR 1.06 95% CI 1.04-1.08). However, the adjusted model did not show a significant association in that direction (aOR 0.96 95% CI 0.93-0.98).

4.1 Main Findings

This large cohort study of an entire obstetric population demonstrated a significant increase in risk of OASI, episiotomies and PPH with longer second stage of labour. As second stage of labour duration increased, the number of caesarean sections and forceps deliveries also increased while SVD fell in both cohorts. A significant association between the duration of second stage of labour and adverse perinatal outcomes was not identified.

4.2 Findings in the context of existing literature

A 2006 systematic review [5] did not establish an optimal duration of second stage of labour, partly citing the dichotomous approach to second stage duration (< vs. > a certain duration [9-11] in most studies), as well as insufficient adjustment of confounders [11, 12].

More recently, large retrospective cohort studies have reported that prolonged second stage of labour is linked to chorioamnionitis and OASI [13, 14], alongside birth asphyxia and admission to NICU [13-16]. The increased risk of NICU admission has been previously reported as 1.35-1.85 [12]. A secondary analysis of trials with women pushing with an epidural found PPH and intrapartum fever increased with longer durations as well as the increased risk of asphyxia [17], while another trial did not identify the same risk for newborns [18].

The findings of this study support the earlier evidence which highlights an increased risk of PPH and OASI without an increased risk to perinatal outcomes as the duration of second stage increases. The lack of statistically significant association between duration of second stage of labour and adverse perinatal outcomes in this study may be explained by any indication of fetal compromise as duration of second stage increases being more likely to prompt the decision to deliver by caesarean or forceps-assisted birth. Incidentally, we found an increase in the rate of NICU admissions with increasing duration of second stage but this was not statistically significant once adjusted for forceps or caesarean delivery.

4.3 Clinical implications

As the duration of second stage increased, forceps delivery and episiotomies became more likely. Many feel the perceptions of forceps and episiotomies have worsened with the public and that caesareans are more acceptable such that these findings have the potential to influence earlier intervention by Caesarean delivery [19]. The changing picture of mode of birth as the second stage of labour extends is visually represented by Figure 1 and 2. The increased risk of PPH and OASI was also significant. As such there is a need to address this issue in nulliparous antenatal counselling by exploring their wishes in a scenario of prolonged second stage of labour.

4.4 Strengths and weaknesses

In total, the cohort captured 1409 births that had a second stage of labour 5 hours or longer. The opportunity to study very prolonged second stage of labour has facilitated a deeper understanding of how the duration impacts outcomes rather than a dichotomous analysis of duration.

The large cohort which captured 51689 births allowed for an analysis that accounted multiple potential confounders, including mode of birth. In the 2006 review, the average population size under review was dramatically smaller than the AMND cohort at 7354, with the largest of them having 25069 mothers [20].

The AMND created a unique opportunity for this analysis due to the local guideline changes.

The duration of labour across the cohort was heavily populated with mothers delivering before 3 hours. This is especially true for the parous women (25548/26337=97%). It means the cohorts of women delivering > 3 hours (3% in parous women) does not have the same level of evidence. However, the study was sufficiently powered to allow for this uneven distribution in most parameters.

Other studies split the cohort between those receiving an epidural or not [21]. Although epidurals may influence both the duration and mode of birth, they were adjusted for in the multivariate analysis. The split by nulliparous/parous appears more appropriate since this is known before going into labour and cannot be changed compared to epidurals.

Prolonged second stage of labour is associated with a significantly increased risk of OASI, having an episiotomy, PPH, forceps-assisted birth and caesarean sections. No association was found with adverse perinatal outcomes. Subsequently, low-risk mothers may wish to prolong the second stage beyond the current national guidance if prioritising a vaginal birth as long as other parameters remain normal.

Postpartum Hemorrhage (PPH
Obstetric Anal Sphincter Injury (OASI)
Aberdeen Maternity and Neonatal Databank (AMND)
Neonatal Intensive Care Unit (NICU)
Odds Ratio (OR)
Confidence Intervals (CI)
Spontaneous Vaginal Deliveries (SVDs)

Ethical approval and consent to participate: Study approval was gained from the AMND steering committee, which has ethical approval from the North of Scotland Research Ethics Service for studies which utilise anonymised unlinked data (19/NS/0079).

Consent for publication: Not applicable.

Availability of data and materials: The datasets used and analysed during the current study are available from the corresponding author on reasonable request via an application to the steering committee of the Aberdeen Maternity and Neonatal Databank. There is a financial cost for the service..

Competing interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding: This work was supported by Vacation Scholarship from Medical Research Scotland (No. Vac-1509-2019). The funders had no involvement in the study design, data collection and analysis, interpretation of data and preparation of the manuscript.

Author contributions:

Conception and design: MB

Data analysis: CY, MB, SB, AR

Manuscript draft: CY, MB, SB, AW, AI, NS

Critical revision: CY, MB, SB, AW

Acknowledgements: Not applicable.

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No competing interests reported.

Augustappendices.docx

Maternal and perinatal outcomes of prolonged second stage of labour: a historical cohort study of over 51,000 women

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Methods

3. Results

4. Discussion

5. Conclusion

Abbreviations

Declarations

References

Additional Declarations

Supplementary Files

Status:

Journal Publication

Version 1