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\begin{document}

\title{Association between intravenous fluids during labour and primary
postpartum haemorrhage: A retrospective cohort study}



\author[1]{Belinda R. BRUCE}%
\author[1]{Heather L. SHEPHERD}%
\author[2]{Saleem AHMED KHAN}%
\author[2]{Charlotte R. HAUNTON}%
\author[1]{Julie LEASK}%
\author[2]{Bradley de Vries}%
\affil[1]{The University of Sydney Susan Wakil School of Nursing and Midwifery}%
\affil[2]{Royal Prince Alfred Hospital Women and Babies Ambulatory Care}%


\vspace{-1em}



  
  \date{May 26, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
\textbf{Objective:} To evaluate whether the administration of
high-volume intravenous (IV) fluids during labour ([?] 2500 mL) increases
the risk of primary postpartum haemorrhage (PPH) and other adverse
outcomes for women with a term, singleton pregnancy, in comparison to
low-volume IV fluids during labour (\textless{}2500 mL).
\textbf{Design:} Retrospective cohort study \textbf{Setting:} Tertiary
referral hospital in Sydney, Australia \textbf{Sample:} 1023 women with
a live singleton fetus in a cephalic presentation; planning a vaginal
birth; and admitted for labour and birth care between 37 - 42 weeks
gestation. \textbf{Methods:} The study factor was IV fluids during
labour. Birth and postnatal data were obtained from electronic medical
records and paper fluid order documentation. Multivariable logistic
regression and multiple imputation were used to explore the relationship
between volume of IV fluids in labour and PPH. \textbf{Main outcome
measures:} The primary outcome was primary PPH [?] 500mL. Secondary
outcomes included caesarean section and major perineal injury.
\textbf{Results:} 1023 participants were included of which 339 had a
primary PPH (33.1\%). There was no association between high-volume IV
fluids and PPH after adjusting for demographic and clinical factors
(Adjusted odds ratio {[}OR \textsubscript{adj}{]}1.02 95\% confidence
interval {[}95\%CI{]} 0.72, 1.44). However, there was a positive
association between high-volume IV fluids and caesarean section (OR
\textsubscript{adj} 1.99; 95\%CI 1.4, 2.8). \textbf{Conclusion:} These
findings are important to further knowledge relating to administration
of IV fluids in labour and the potential impact of this common practice.
It identifies future research priorities around documentation of IV
fluids and their relationship with pregnancy and perinatal outcomes.%
\end{abstract}%



\sloppy


\subsection*{TITLE PAGE}

{\label{title-page}}

\subsection*{Manuscript Title}

{\label{manuscript-title}}

Association between intravenous fluids during labour and primary
postpartum haemorrhage: A retrospective cohort study

\subsection*{Authors}

{\label{authors}}

Ms Belinda R. BRUCE\textsuperscript{1,2}

Dr Heather L. SHEPHERD\textsuperscript{1}

Mr Saleem AHMED KHAN\textsuperscript{3}

Dr Charlotte R. HAUNTON\textsuperscript{3}

Professor Julie LEASK\textsuperscript{1,4}

A/Professor Bradley S. DE VRIES\textsuperscript{2,5}

\textsuperscript{1}Susan Wakil School of Nursing and Midwifery, Faculty
of Medicine and Health, The University of Sydney, NSW, Australia,

\textsuperscript{2}Sydney Institute for Women, Children and their
Families, RPA Women and Babies, Royal Prince Alfred Hospital, Sydney
Local Health District, NSW, Australia

\textsuperscript{3}RPA Women and Babies, Royal Prince Alfred Hospital,
Sydney Local Health District, NSW, Australia

\textsuperscript{4}School of Public Health, Faculty of Medicine and
Health, The University of Sydney, NSW, Australia,

\textsuperscript{5}Central Clinical School, Faculty of Medicine and
Health, The University of Sydney, NSW, Australia

\subsection*{Corresponding Author}

{\label{corresponding-author}}

Belinda BRUCE PhD Candidate

Susan Wakil School of Nursing and Midwifery, Faculty of Medicine and
Health,

D18 Susan Wakil Health Building, Western Avenue,

The University of Sydney, NSW, Australia, 2006

Email: belinda.bruce@sydney.edu.au

\textbf{Running title}

IV Fluids in Labor \& Postpartum Haemorrhage

\textbf{Keywords}

Intravenous Fluids, Labour, Intrapartum Care, Postpartum Hemorrhage,
Fluid Management, Maternal outcomes

\textbf{Funding}

This research received no specific grant from any funding agency in the
public, commercial, or not-for-profit sectors.

\textbf{ABSTRACT}

\textbf{Objective:} To evaluate whether the administration of
high-volume intravenous (IV) fluids during labour ([?] 2500 mL) increases
the risk of primary postpartum haemorrhage (PPH) and other adverse
outcomes for women with a term, singleton pregnancy, in comparison to
low-volume IV fluids during labour (\textless{}2500 mL).

\textbf{Design:} Retrospective cohort study

\textbf{Setting:} Tertiary referral hospital in Sydney, Australia

\textbf{Sample:} 1023 women with a live singleton fetus in a cephalic
presentation; planning a vaginal birth; and admitted for labour and
birth care between 37 - 42 weeks gestation.

\textbf{Methods:} The study factor was IV fluids during labour. Birth
and postnatal data were obtained from electronic medical records and
paper fluid order documentation. Multivariable logistic regression and
multiple imputation were used to explore the relationship between volume
of IV fluids in labour and PPH.

\textbf{Main outcome measures:} The primary outcome was primary PPH [?]
500mL. Secondary outcomes included caesarean section and major perineal
injury.

\textbf{Results:} 1023 participants were included of which 339 had a
primary PPH (33.1\%). There was no association between high-volume IV
fluids and PPH after adjusting for demographic and clinical factors
(Adjusted odds ratio {[}OR\textsubscript{adj}{]}1.02 95\% confidence
interval {[}95\%CI{]} 0.72, 1.44). However, there was a positive
association between high-volume IV fluids and caesarean section
(OR\textsubscript{adj} 1.99; 95\%CI 1.4, 2.8).

\textbf{Conclusion:} These findings are important to further knowledge
relating to administration of IV fluids in labour and the potential
impact of this common practice. It identifies future research priorities
around documentation of IV fluids and their relationship with pregnancy
and perinatal outcomes.

\textbf{MAIN MANUSCRIPT}

\textbf{1.0 Introduction}

Primary postpartum haemorrhage (PPH) is one of the most common
complications of childbirth and a major cause of maternal mortality and
morbidity worldwide.(1-5) The World Health Organization (WHO) defines
primary PPH as a maternal blood loss [?] 500 mL within the first 24 hours
of giving birth.(4, 5) Women who experience a primary PPH commonly
require greater levels of clinical intervention and care immediately
after the birth of their child and into the postpartum period.(6)

The most common cause of primary PPH is uterine atony contributing to
70-80\% of all primary PPHs.(2) In high income countries such as
Australia, France, Canada, the United Kingdom (UK) and the United States
of America (USA) there has been an increased incidence of primary atonic
PPH in the last 10-20 years.(3, 6-9) However, this increase is not fully
explained with changes in known risk factors or reporting.(3)

One intervention that is anecdotally considered a potential risk factor
for primary PPH is the administration of intravenous (IV) fluids during
labour. The use of IV fluids as part of labour care is common in high
income countries such as Australia, Canada, and the USA.(10-14) It is
biologically plausible a potential relationship exists whereby larger
volumes of IV fluids could impair uterine contractility through the
development of uterine swelling (15) and/or metabolic acidosis. (16)
Additionally, dilution of clotting factors (coagulopathy)(16) or
endogenous oxytocin could be possible mechanisms. If true, these could
contribute to atonic PPH by inhibiting the myometrium from efficiently
contracting onto exposed blood vessels after placental separation and/or
preventing blood to clot effectively.

The aim of this study was to investigate whether there is a relationship
between the administration of IV fluids during labour and primary PPH.
The primary objective was to evaluate whether the administration of
high-volume IV fluids during labour ([?] 2500 mL) increases the risk of
primary PPH for women with a term gestation, singleton pregnancy, in
comparison to low-volume IV fluids during labour (\textless{}2500 mL).

\textbf{2.0 Methods}

\textbf{2.1 Study design}

This was a single-site retrospective cohort study. The study factor was
exposure to IV fluids during labour and the primary outcome was PPH.
This study is reported using STROBE guidelines.(17)

\textbf{2.2 Participants}

All women who birthed at a metropolitan tertiary referral hospital in
Sydney, Australia between 1\textsuperscript{st} September 2021 and
31\textsuperscript{st} October 2022 who met the inclusion criteria were
eligible for the study. Inclusion criteria were: a live singleton fetus
in a cephalic presentation; planned vaginal birth; and admitted for
labour and birth care between 37\textsuperscript{+0} weeks and
42\textsuperscript{+0} weeks gestation. Exclusion criteria were: IV
fluid data or estimated maternal blood loss documentation insufficient
and/or missing. Participants received routine care including the intake
of oral fluids and the administration of 10 units oxytocin
intramuscularly at birth to prevent PPH, with a second dose if greater
than expected blood loss or uterine atony were observed.

\textbf{2.3 Study variables}

Primary PPH was defined as maternal blood loss [?] 500ml within 24 hours
after birth. The data sources included the hospital's clinical
electronic database, electronic medical records and paper fluid order
documentation. Maternal estimated blood loss (EBL) was extracted from
the hospital's clinical electronic database. In cases where EBL was
missing from the clinical electronic database, case documentation was
reviewed by the lead author to identify the clinician recorded EBL
within the written electronic progress notes. The total volume of IV
fluids administered was determined by reviewing related documentation
within the clinical electronic database, electronic medical records, and
paper fluid order documentation. The total volume of IV fluids
administered was calculated from the point of first administration
during labour to the time of birth. While the complete medical records
(electronic and paper fluid order documentation) consistently recorded
the total number of bags of fluids prescribed, it was often unclear what
proportion of the final bag of fluids had been administered before the
time of birth due to unreliable documentation of IV fluid administration
rates in the electronic clinical records. Total intrapartum IV fluid
volume was therefore manually estimated by determining the duration of
time over which the previous bag of fluids was administered, calculating
the rate (in mL/hr), and applying this rate to the final bag. In cases
where a single bag of IV fluids was administered, the rate could not be
determined, and it was assumed that the total bag volume (including the
additional volume of any oxytocin) was administered by time of birth.

Secondary outcomes included: Severe primary PPH (defined as maternal
blood loss [?] 1000 mL within 24 hours after birth); atonic PPH; immediate
PPH management; blood product transfusion; major perineal injury ([?] 3rd
degree perineal injury); and caesarean section birth. Additionally,
variables were collected as co-variates, these included: birth weight;
maternal pyrexia ([?] 38 \selectlanguage{ngerman}°C on at least one occasion during labour);
intrapartum IV antibiotics for infection; duration of active labour
(from the time of regular uterine contractions with the cervix \selectlanguage{english}[?] 4cm
dilated to the time of birth); epidural anaesthesia during labour;
instrumental birth; emergency caesarean section; genital tract injury;
retained placenta/membranes; hypertensive disorders of pregnancy; model
of care; body mass index (BMI); and parity. Baseline characteristics and
demographic variables were collected in accordance with the Core
Outcomes in Women's and Newborn Health (CROWN) initiative.(18)



\textbf{2.4 Study sample size}

Study sample size was calculated using the odds ratio for multiple
logistic regression for a binary outcome using the method described by
Hsieh et al.(19) We assumed an alpha value of 0.05, a beta value of 0.2,
P1 (rate of PPH in the unexposed group) of 20\%, an odds ratio of 1.65
(a relative risk of approximately 1.5), and B (proportion of the
population exposed to IV fluid \selectlanguage{english}[?] 2500 mL) = 50\%. This gave a required
sample size of 686. We then calculated the R2 using data from a previous
study(11) to estimate that 32\% of the variance in the use of IV fluids
was due to the covariates and adjusted the sample size using a variance
inflation factor of 1.47 {[}=1/(1-R2){]} to calculate the final required
sample size of 1009 participants.

\textbf{2.5 Statistical analysis}

The analysis was performed using the statistical software program SAS
version 9.4(20). Descriptive statistics included means and standard
deviations for parametric data, medians and interquartile ranges for
non-parametric data and percentages for categorical data. Multivariable
logistic regression was used to explore the relationship between volume
of IV fluids in labour (high volume versus low volume) and estimated
maternal blood loss \selectlanguage{english}[?]500 mL. A p value of \textless{}0.05 was considered
statistically significant. Explanatory variables were determined prior
to the analysis based on a review of the current literature. These were:
maternal age, BMI, country of origin, parity, model of care, IV
antibiotics for infection/suspected infection, type of birth, degree of
perineal injury, duration of active labour, and birth weight. Continuous
explanatory variables (e.g. maternal age, BMI, and birthweight) were
tested for linear association by sorting into clinically relevant groups
(e.g., maternal age \textless{}25, 25-29, 30-34, and \selectlanguage{english}[?]35 years) and
plotting the beta-coefficients against the midpoints for each group.
Variables without linearity were analysed by these groups. Multiple
imputation was attended for missing data using 20 iterations. Logistic
regression was performed on each of the 20 datasets and summary
regression parameters were reported.

\textbf{2.6 Ethics Approval}

Human Research Ethics Committee approval was gained through Sydney Local
Health District on the 27th of April 2020 (Protocol No. X19-0430 \&
2019/ETH13385).

\textbf{3.0 Results}

A total of 1403 cases were reviewed. After exclusions for insufficient
IV fluids documentation, 1023 cases were included in the analysis
(Figure 1). The volume of IV fluids administered ranged from 0 mL to
5751 mL. Two types of crystalloid IV fluids were used: 0.9\% Normal
Saline and Hartmann's solution (Compound Sodium Lactate). These were
administered at variable rates. The low-volume IV fluids group
(\textless{}2500 mL) included 810 cases, and the high-volume IV fluids
group (\selectlanguage{english}[?]2500 mL) included 213 cases. Maternal demographics and clinical
characteristics for the two groups are summarised in Table 1 and Table
2.

\textbf{3.1 Primary Postpartum Haemorrghage (PPH)}

A total of 339 women had a primary PPH (EBL \selectlanguage{english}[?] 500mL) (33.1\%), with
252/810 women (31.1\%) in the low-volume IV fluids group and 87/213
(40.8\%) in the high-volume IV fluids group. Sixty-four (7.9\%) in the
low-volume group and 24 (11.3\%) in the high-volume group had a severe
primary PPH (EBL \selectlanguage{english}[?] 1000mL). There was a positive association between
high-volume IV fluids and primary PPH \selectlanguage{english}[?] 500 mL in the univariable
logistic regression (odds ratio {[}OR{]} 1.53 95\% confidence interval
{[}CI{]}: 1.12, 2.09). However, the OR decreased to 1.02 (95\% CI: 0.72,
1.44) and statistical significance was not reached in the multiple
logistic regression (Table 3).

\textbf{3.2 Maternal estimated blood loss (EBL)}

Maternal estimated blood loss ranged from 40 mL to 3400 mL for the
cohort (median 350 mL, IQR 300-600 mL). The median EBL for the
low-volume IV fluids group was 350 mL (IQR 250-500 mL) and 400 mL (IQR
300-600 mL) for the high-volume IV fluids group (Wilcoxon rank sum test,
p = 0.003).

\textbf{3.3 Incidence of atonic PPH}

Due to insufficient documentation, it was unable to be ascertained
retrospectively whether uterine atony was the principal cause of the
observed PPHs.

\textbf{3.4 Immediate PPH management}

A majority of the sample (62.2\%) were administered a 40 units oxytocin
infusion in the postpartum period for either PPH prophylaxis or PPH
management: 471/810 (58.1\%) in the low-volume IV fluids group and
165/213 (77.5\%) in the high-volume IV fluids group. It was not possible
to collect the specifics of further medical and/or surgical management
of PPH in this retrospective study.

\textbf{3.5 Postpartum Red Blood Cell Transfusion}

A total of fifteen women required a postpartum red blood cell
transfusion (1.5\%), 11/810 (1.4\%) in the low-volume IV fluids group
and 4/213 (1.9\%) in the high-volume IV fluids group. Additionally, one
woman required a repeat red blood cell transfusion the following day in
the low-volume IV fluids group. Due to the low number of events, a
regression analysis to test for an association with IV fluids
administration was not performed.

\selectlanguage{english}\textbf{3.6 Major Perineal injury ([?] 3\textsuperscript{rd} degree
perineal injury)}

A total of 27 women out of the 745 women who had a vaginal birth (3.6\%)
sustained a major perineal injury. Due to the low number of events,
categorical covariates in the multivariable logistic regression were
condensed into fewer categories (Table S1). Parity, country of origin
(surrogate for ethnicity), use of forceps and birthweight were included
in the model as they are recognised risk factors for obstetric anal
sphincter injury. Volume of IV fluids was associated with major perineal
injury in the univariable regression (OR\textsubscript{unadj} 2.5; 95\%
CI: 1.07, 5.9). However, in the multivariable logistic regression, only
the use of forceps was associated with major perineal injury
(OR\textsubscript{adj} 3.0 95\% CI: 1.2, 7.6) (Table S1).

\textbf{3.7 Emergency Caesarean section}

Overall, 278 women had an emergency caesarean section (27.2\%), 176/810
(21.7\%) women in the low-volume IV fluids group, and 102/213 (47.9\%)
women in the high-volume IV fluids group. The unadjusted logistic
regression showed that women in the high-volume IV fluids group were
more likely to have an emergency caesarean section than women in the
low-volume IV fluids group (OR\textsubscript{unadj} 3.3; 95\% CI: 2.4,
4.5). In the adjusted model, emergency caesarean section remained
associated with high-volume IV fluids after adjusting for maternal age,
birth weight, BMI, Intrapartum IV antibiotics for infection/suspected
infection, maternal origin, parity, previous caesarean section, length
of active labour, and model of care (OR\textsubscript{adj} 1.99; 95\%
CI: 1.4, 2.8) (Table S2). Additionally, women born in South-East Asia
(OR\textsubscript{adj} 1.5; 95\% CI: 1.008, 2.3), duration of active
labour \selectlanguage{english}[?] 12 hours (OR\textsubscript{adj} 1.6; 95\% CI: 1.04, 2.5), and
neonatal birthweight \selectlanguage{english}[?] 4000 grams (OR\textsubscript{adj} 2.4; 95\% CI:
1.3, 4.4) were associated with emergency caesarean section in the
adjusted model (Table S2).

\textbf{4.0 Discussion}

\textbf{4.1 Main Findings}

This study did not find an association between high volume IV fluids and
PPH after adjusting for demographic and clinical factors. PPH \selectlanguage{english}[?] 500 mL
was associated with maternal BMI \selectlanguage{english}[?] 35, nulliparity, women born in
South-East Asia, emergency caesarean birth, and birth weight \selectlanguage{english}[?] 4kg.
Maternal BMI\textgreater{}35 and duration of active labour \selectlanguage{english}[?] 12 hours
was associated with PPH \selectlanguage{english}[?] 1000 mL after adjusting for confounding
factors. These associations were expected and supports the findings of
other research exploring risk factors for PPH. (7, 8, 21-23) A second
unexpected finding was the positive association between high-volume IV
fluids and emergency caesarean section.

\textbf{4.2 Interpretation}

Our study found women were more likely to require an emergency caesarean
section if they received \selectlanguage{english}[?] 2500 mL IV fluids compared to \textless{}2500
mL. This finding is in contrast to Coco et al. (24) and Garite et
al.(14) that reported no statistical difference for total caesarean
sections in their randomised controlled trials (RCTs) evaluating
increased rates of IV fluids to nulliparous women in spontaneous labour.
Duffy et al.(13) also reported no statistical difference in caesarean
section rates for their more recent RCT examining increased IV hydration
in nulliparous women undergoing induction of labour. However, it is
important to note that our study included both nulliparous and parous
women, in either spontaneous, augmented, or induced labour, and had a
much larger sample size than these three RCTs. Similarities included the
IV fluid types and the overall total volume administered between
intervention and controls, with both Coco et al.(24) and Garite et
al.(14) reporting total IV fluids volumes of approximately 2500 mL or
greater for their increased IV fluids group. In contrast, Duffy et
al.(13) reported much larger mean IV fluids volumes of 3476.8 mL for
their 125 mL/hr group and 6984.5 mL for their 250 mL/hr group. PPH was
not a reported outcome of Duffy et al.(13)

Whilst our study was not designed to answer the specifics as to why this
result may have occurred, it is conceivable that IV fluids in labour may
influence the power, passenger, or passage. For example, through
increased fetal weight from the transfer of additional IV fluids across
the placenta.(25, 26) Additionally, there is biological plausibility
that altered uterine contractility related to IV fluids administration
could increase the risk of emergency caesarean section.(15) In the work
by Moen et al.,(27) there was a statistically significant correlation
between perinatal hyponatraemia (plasma sodium levels \textless{}130
mmol/L) and emergency caesarean section for slow progress in labour. Our
results support the need for further prospective research, ideally
larger sized RCTs examining the administration of IV fluids in labour
and maternal outcomes such as emergency caesarean section for slow
progress in labour.

Finally, our observed rates of PPH \selectlanguage{english}[?] 500 mL and PPH \selectlanguage{english}[?] 1000 mL of 33.1\%
and 8.6\% of births respectively were higher than expected. In 2021, the
rate of PPH within Australia was approximately 21\%. (28) However, the
true rate may be higher, with differences in definitions and reporting
methods possibly contributing to underreporting.(6, 7) The rate of PPH
in this study was comparable to a UK cohort examined by Briley et al.
(7) who reported a 33.7\% incidence for PPH \selectlanguage{english}[?] 500 mL and 3.9\% for PPH \selectlanguage{english}[?]
1000 mL. The authors reported that to the best of their knowledge, it
was the highest incidence of PPH reported from any high-income or
low-income country and concluded that there is a need for policy and
research to focus on potentially modifiable risk factors for PPH.(7)
This sentiment is echoed by the World Health Organization and in
Australia, with the prevention and management of primary PPH seen as an
area of research priority due to the potential for maternal death and
negative long-term health impacts for both mother and baby.(29, 30)

\textbf{4.3 Limitations}

The main limitation of this study was inadequate documentation of
maternal fluid balance. This limitation has been encountered by other
researchers investigating intrapartum IV fluids practices. (11, 31, 32)
In our study inadequate documentation necessitated the exclusion of
certain cases and the assumption of consistent IV fluids administration
rates continued between bags. Whilst this approached helped to mitigate
selection bias and uphold the study's internal validity, there remains
the potential that non-differential misclassification of IV fluids
volume occurred. Moreover, the necessity to categorise IV fluids intake
into two groups may have diluted our findings and increased the risk of
a Type 2 error (failing to reject a false null hypothesis).

A second limitation of this study was the visual estimation of maternal
blood loss. Maternal blood loss at birth can be underestimated when
visual estimation is used.(7, 33) Consequently, maternal blood loss may
have been systematically underestimated, particularly given the
infrequent documentation of cumulative blood loss within the initial 24
hours postpartum.

\textbf{4.4 Future Research}

Currently, a large evidence gap exists regarding the administration of
IV fluids during labour and their effects on maternal and neonatal
outcomes. Reporting of common practices for IV fluids administration in
labour is limited. Addressing this knowledge gap is important for
designing future prospective studies that accurately reflect
interventions used in clinical practice. Whilst RCTs may be helpful in
exploring maternal and neonatal outcomes, without knowing what `usual
practice' is, the tested interventions may not reflect current practice,
limiting any knowledge gain.

Inadequate documentation of maternal fluid balance is a key barrier to
rigorous prospective research in this area due to the imprecise
recording of the exposure variable. Considering the potential impact of
IV fluids on labour, including disruptions to electrolyte balance and
uterine contractility, events such as IV fluid boluses and interruptions
in IV infusion may hold considerable importance. Adopting practices that
enhance the documentation of maternal fluid balance, such as integrating
implementation science methods and frameworks to support health service
engagement, identify workflow logistics and promote behaviour
change,(34-36) could prove advantageous in future research .



\textbf{5.0 Conclusion}

This study found that there was not an association between high volume
IV fluids and PPH after adjusting for demographic and clinical factors
for this cohort of women at a single, metropolitan, tertiary referral
hospital. However, there was a positive association between high-volume
IV fluids and emergency caesarean section. Overall, these findings are
important to further knowledge relating to the administration of IV
fluids in labour and the potential impact of this common practice. It
identifies future research priorities around documentation of IV fluids
and their relationship with pregnancy and perinatal outcomes.

\textbf{6.0 Funding statement}

This research received no specific grant from any funding agency in the
public, commercial, or not-for-profit sectors.

\textbf{7.0 Author Contributions}

BB: Conceptualisation, methods, validation, investigation, resources,
data curation, data analysis, writing -- original draft preparation,
writing -- review and editing, visualisation, project administration.
HS: methods, writing - review and editing, resources, supervision; SK:
methods, investigation, resources, writing - review and editing. CH:
investigation, writing- review and editing. JL: Conceptualisation,
methods, writing - review and editing, resources, supervision. BdV:
Conceptualisation, methods, validation, investigation, data analysis,
writing - review and editing, resources, supervision.

\textbf{8.0 Conflict of Interest}

No conflict of interest has been declared by the authors.

\textbf{9.0 Patient or public consultation}

This study was presented at a peer review research meeting at the study
site during the planning stages of the study. No other patient or public
consultation was attended.



\textbf{10.0 Acknowledgments}

We would like to acknowledge Colleen Certoma and Rebecca Grange for
their help and support throughout the conduct of this study. Both
provided support through the Covid-19 pandemic to facilitate the conduct
of this study and their efforts were appreciated. The lead author would
also like to acknowledge Emily Leefhelm for her support throughout this
study.



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Best Practice \& Research Clinical Anaesthesiology. 2022;36(3-4):325-39.

2. Mousa HA, Blum J, Abou El Senoun G, Shakur H, Alfirevic Z. Treatment
for primary postpartum haemorrhage. Cochrane Database Syst Rev. 2014(2).

3. Knight M, Callaghan WM, Berg C, Alexander S, Bouvier-Colle M-H, Ford
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\textbf{Hosted file}

\verb`Figure 1 participant flow chart.docx`  available at \url{https://authorea.com/users/759217/articles/733655-association-between-intravenous-fluids-during-labour-and-primary-postpartum-haemorrhage-a-retrospective-cohort-study}

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\verb`Table 1 Demographic characteristics of 1023 women planning a vaginal birth at 37 or more weeks\selectlanguage{english}' gestational age.docx`  available at \url{https://authorea.com/users/759217/articles/733655-association-between-intravenous-fluids-during-labour-and-primary-postpartum-haemorrhage-a-retrospective-cohort-study}

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\verb`Table 2 Clinical characteristics of 1023 planning a vaginal birth at 37 or more weeks gestational age.docx`  available at \url{https://authorea.com/users/759217/articles/733655-association-between-intravenous-fluids-during-labour-and-primary-postpartum-haemorrhage-a-retrospective-cohort-study}

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\verb`Table 3 Multiple imputation and logistic regression for postpartum haemorrhage among 1023 women planning a vaginal birth at 37 or more weeks gestational age.docx`  available at \url{https://authorea.com/users/759217/articles/733655-association-between-intravenous-fluids-during-labour-and-primary-postpartum-haemorrhage-a-retrospective-cohort-study}

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\verb`Table S1 Multiple imputation and logistic regression for severe perineal injury.docx`  available at \url{https://authorea.com/users/759217/articles/733655-association-between-intravenous-fluids-during-labour-and-primary-postpartum-haemorrhage-a-retrospective-cohort-study}

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\verb`Table S2 Multiple imputation and logistic regression for emergency lscs.docx`  available at \url{https://authorea.com/users/759217/articles/733655-association-between-intravenous-fluids-during-labour-and-primary-postpartum-haemorrhage-a-retrospective-cohort-study}

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