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obstetric anal sphincter injury

at childbirth

Amanda Jane Ampt

Thesis by published works

Submitted in fulfilment of the requirements for the degree

of

Doctor of Philosophy

Kolling Institute of Medical Research

Faculty of Medicine

University of Sydney

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The primary aims of the research presented in this thesis were to examine the relationship between rising obstetric anal sphincter injury (OASI) rates in New South Wales (NSW) Australia and the associated clinical and demographic factors; to determine the recurrence risk and risk factors; to evaluate the impact of data sources; and to establish which perineal support practices midwives prefer to use in different clinical scenarios.

Methods

Investigation into OASI trends, risk factors, recurrence and the effect of data source was undertaken using two linked population health datasets: the NSW Perinatal Data Collection (known as birth data) and the Admitted Patient Data Collection (known as hospital data). The study populations were based on all births in NSW from 2001 to 2009, and when data

became available, from 2001 to 2011. Logistic regression and predictive modelling were used to investigate risk factors and recurrence, and trends in adjusted odds ratios (aORs) for

different birth modes over time were compared. Comparison between the use of birth data and hospital data in a linked dataset was undertaken for OASI ascertainment using Kappa and agreement statistics, and comparison of the adjusted risk factor estimates was also carried out. Investigation into NSW midwifery practice was undertaken by a survey conducted at five public hospitals, with results presented using descriptive analysis, McNemar and chi-squared tests.

Results

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 Significant risk factors for primiparous women included: instrumental births with aORs ranging from 1.80 (95% CI 1.70, 1.93) among vacuum births with episiotomy to 6.10 (95% CI 5.56, 6.70) among forceps without episiotomy; non-instrumental birth with episiotomy (aOR 1.20 95% CI 1.12, 1.29); Asian country of birth (aOR 2.03 95% CI 1.93, 2.14); increasing birthweight (aOR 1.21 per 200 gram increments; 95 %CI 1.19, 1.22); and male infant (aOR 1.08 95% CI 1.03, 1.12). The age group with the highest risk was among 25–34 year olds. Regional analgesia was associated with decreased likelihood of an OASI (aOR 0.91 95% CI 0.87, 0.96).

 Significant risk factors for multiparous women included: instrumental births, with

aORs ranging from 2.60 (95% CI 2.16, 3.13) among vacuum births with episiotomy to 6.15 (95% CI 4.98, 7.58) among forceps without episiotomy; non-instrumental birth with episiotomy (aOR 2.02 95% CI 1.79, 2.27); Asian country of birth (aOR 2.19 95% CI 1.99, 2.40); increasing birthweight (aOR 1.25 per 200 gram increments; 95%CI 2.13, 1.27); and male infant (aOR 1.13 95% CI 1.06, 1.22). The age group with the highest risk was among 30–39 year olds. Unlike primiparas, diabetes (aOR 1.24 95%CI 1.07, 1.44), gestational age ≥41 completed weeks (aOR 1.13 95% CI 1.03, 1.24) and regional analgesia (aOR 1.25 95% CI 1.14, 1.38) were risk factors. Multiparous women with no previous vaginal birth were also at high risk (aOR 5.61 95% CI 5.05, 6.23).

 Risk factors did show prevalence changes across the years, for example, the proportion

of women born in Asian countries and the use of regional analgesia for multiparous women increased; others decreased, for example, non-instrumental births with

episiotomy and post term infants among multiparous women. The prevalence of other risk factors remained constant, for example, high infant birthweight.

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 For women having an OASI at the first birth and another vaginal birth at their second, the OASI first birth risk was 4.5% and the recurrence risk was 5.7%. This relatively modest increase may reflect appropriate decision-making for second birth mode, with 19.4% having a pre-labour caesarean section. Risk factors included higher birthweight at the second birth and diabetes at the first; while birthweight ≥4.0 kg at the first birth and 37–38 weeks gestation at the second birth were associated with decreased

likelihood of recurrence.

 Increases in adjusted risk of OASI across the years were evident for women with a

non-instrumental birth and no episiotomy (p<0.01), and for women with a forceps birth without episiotomy (p<0.01). Other birth types did not show significant increases in risk for OASI.

 Data source influenced OASI ascertainment, with rates of OASI calculated for 2001–

2011 of 2.1% by birth data alone, and 2.6% by linked hospital data. With changes to the birth data collection form, ascertainment and agreement improved between birth and hospital data; however, birth data still under-reported OASI. Episiotomy was a risk factor for OASI using linked data (aOR 1.34 95% CI 1.27, 1.41), but non-significant when birth data alone were used (aOR 1.03 95% CI 0.97, 1.09).

 Of the 141 midwives eligible to participate in the survey of perineal practice, 108

responded (response rate of 76.6%). The majority of midwives preferred to use ‘hands poised’ approach (n=68, 63.0%), with very small numbers (n=5, 4.6%) preferring ‘hands off’. Midwives reported changing practice in scenarios of greater risk for OASI, with a total of 83.4% using a ‘hands on’ approach if they were concerned about an impending OASI. There has been a shift over time from teaching ‘hands on’ to

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risk factors available in population datasets. The increase is significant in only two birth modes: non-instrumental without episiotomy and forceps with episiotomy. There is an ecological association with a ‘hands poised or off’ approach and rising OASI rate among non-instrumental births without episiotomy; however, midwives report they switch to ‘hands on’ if concerned about an impending possible OASI. Researchers need to be aware that reporting of OASI rates by birth data alone may lead to under-ascertainment.

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This thesis presents a body of work that has evolved and developed over time. The primary aim was to investigate the trend of rising obstetric anal sphincter (OASI) rates documented by the New South Wales (NSW) Ministry of Health in its annual Mothers and Babies reports. At the time of embarking on this PhD, no population-based OASI investigation had been

published for NSW. During the course of investigation, several gaps in knowledge were identified which led to further research questions and sub-studies.

Each sub-study is presented in this thesis as a separate chapter (Chapters 2–6). Also part of this related body of research, but not specific to OASI, was a sub-study on data quality which is presented in the Appendix. I am principal author on the sub-studies, all of which have been submitted for publication as the research has been completed. Each has co-authors; however, I was involved in the conception of each study and study design, and was responsible for the data analyses, interpretation of findings and writing of the manuscripts. My supervisor and co-supervisor were responsible for the original broad ideas, and with the other co-authors, provided methodological expertise and contributed to the interpretation of findings and review of manuscripts. Individual statements of authors’ contributions to papers are presented in the Appendix.

The NSW OASI rates were investigated using linked population health data. This work confirmed that OASI rates were rising, but demonstrated that the rising rates were not being driven by changes in risk factors, therefore opening up more questions regarding

identification of other factors. In analysing changing risk across the years within different birth modes, it was hoped that we may be able to pinpoint if unidentified factors were

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Our research group is located on the Royal North Shore Hospital campus, a large tertiary hospital in Sydney, and we are lucky to have considerable collaboration with clinicians. They were particularly interested in risk of recurrence among women with a prior OASI, and how best to counsel them regarding a subsequent birth. This led to the recurrence sub-study, which is presented in Chapter 4 and published in BMC Pregnancy and Childbirth.

Not all researchers have access to linked population data, and we were interested in whether rates of OASI and risk factor estimates would differ between the use of birth data and linked hospital data. While the hospital data has not undergone coding changes around perineal trauma during the study period of 2001–2011, the birth data has. It was timely to investigate the impact of these changes. This study is presented in Chapter 5 and is currently under review at Public Health Research and Practice.

Studies undertaken in Norway reported that changes around perineal support practices may be having an impact on OASI rates. In collaboration with Michelle de Vroome, the Clinical Midwifery Consultant from our Local Health District, we undertook a survey to quantify what current midwifery practice entailed. This also provided me with an opportunity to gain skills in primary data collection, and survey analysis. This analysis has been accepted for publication in the Australian and New Zealand Journal of Obstetrics and Gynaecology and is presented in Chapter 6, with the participant information and consent form provided in the Appendix.

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midwives was approved by the Northern Sydney Local Health District Research Ethics Committee.

This PhD has given me the opportunity to bring together many aspects of my professional interests. Qualifications and experience in midwifery, health information management and epidemiology have all been beneficial in providing me with a skill set as a basis to undertake this research. Experience as a midwife for over fifteen years, which included care to women who experienced adverse outcomes, has been a motivating force for this research. During the course of my PhD, I was also involved as a co-author on five other peer-reviewed papers, two of which specifically related to perineal trauma (episiotomy practices in Viet Nam), one which included investigation of OASI as a risk factor for planned caesarean birth, and two which utilised my previous experience as a lactation consultant.

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have been able to complete my PhD. In particular, I would like to thank my supervisor Associate Professor Jane Ford. Her encouragement, support and research advice have been invaluable and have kept me on track over the past three and a half years. I would also like to thank my associate supervisor, Associate Professor Christine Roberts, whose research

expertise and encouragement have been hugely appreciated. I am most grateful to you both for all your assistance.

I have been blessed to work with other researchers in Building 52 who have given their support and camaraderie; particularly Samantha Lain, Charles Algert, Eleni Mayson, Diana Bond, Jason Bentley, Jillian Patterson, Francisco Schneuer and Natasha Nassar. Gratitude also goes to Michelle de Vroome for her support and enthusiasm.

I am grateful to have been financially supported in my work by the Dr Albert S McKern Research Scholarship, and a postgraduate scholarship in epidemiology and biostatistics (Clinical and Population Perinatal Health Research, Sydney Medical School, University of Sydney).

To my friends Kate, Justine, Trace, Ann and Cath who have provided a listening ear and encouragement, a game of mah-jong, or a dinner, thank you. I would also like to thank my parents, Ted and Patsy Halliday (both now deceased), who instilled in me a sense of purpose and valued education so highly. To my father, thank you for the words of wisdom when I was eight years old, “Girls are good at maths” and then proceeded to do mental arithmetic games with me for many years.

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This thesis is presented for examination as a thesis containing published work. Two of the chapters presented in this thesis have been published in peer-reviewed journals; one has been accepted and is in press; and two are under review. The candidate is the principal author of each paper.

1. Ampt AJ, Ford JB, Roberts CL, Morris JM: Trends in obstetric anal sphincter

injuries and associated risk factors for vaginal singleton term births in New South Wales 2001–2009. Australian and New Zealand Journal of Obstetrics and Gynaecology 2013, 53(1):9-16.

2. Ampt AJ, Patterson JA, Roberts CL, Ford JB: Obstetric anal sphincter injury

(OASI) rates are not rising equally among different vaginal birth modes for primiparous women. Currently under review at International Journal of Gynecology and Obstetrics.

3. Ampt AJ, Roberts CL, Morris JM, Ford JB: The impact of first birth obstetric anal

sphincter injury on the subsequent birth: a population-based linkage study. BMC Pregnancy Childbirth 2015, 15(1):31.

4. Ampt AJ, Ford JB: Ascertainment of severe perineal trauma and associated risk

factors using birth data compared to linked hospital data. Currently under review at Public Health Research and Practice.

5. Ampt AJ, de Vroome M, Ford JB: Perineal management techniques among

midwives at five hospitals in New South Wales - A cross-sectional survey. Accepted for publication at Australian and New Zealand Journal of Obstetrics and Gynaecology.

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Part of related body of research, but not specific to OASI (presented in Appendix):

Ampt AJ, Ford JB, Taylor LK, Roberts, CL: Are pregnancy outcomes associated

with risk factor reporting in routinely collected perinatal data? NSW Public

Health Bulletin 2013, 24(2):65-69

Co-authored during my candidature but not part of this thesis:

1. Chen JS, Ford JB, Ampt A, Simpson JM, Roberts CL: Characteristics in the first

vaginal birth and their association with mode of delivery in the subsequent birth. Paediatric and Perinatal Epidemiology 2013, 27(2):109-117.

2. Trinh AT, Khambalia A, Ampt A, Morris JM, Roberts CL: Episiotomy rate in

Vietnamese-born women in Australia: Support for a change in obstetric practice in Viet Nam. Bulletin of the World Health Organization 2013, 91(5):350-356.

3. Schiff M, Algert C, Ampt A, Sywak M, Roberts C: The impact of cosmetic breast

implants on breastfeeding: a systematic review and meta-analysis. International Breastfeeding Journal 2014, 9:17.

4. Lain S, Ampt A: Mini-Commentary: Population-based or customised birthweight

centiles to detect SGA? BJOG 2014, 121(9):1089.

5. Roberts C, Ampt A, Algert C, Sywak M, Chen J: Reduced breast milk feeding

subsequent to cosmetic breast augmentation surgery. Accepted for publication at The Medical Journal of Australia.

6. Trinh A, Roberts C, Ampt AJ: Knowledge, attitude and experience of episiotomy

use among obstetricians and midwives in Viet Nam. Currently under review at BMC Pregnancy and Childbirth.

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Abstract ... 2

Preface... 6

Acknowledgements ... 9

Publications arising from this thesis ... 11

Additional publications ... 12

Table of contents ... 13

List of abbreviations ... 15

Chapter 1: Background ... 16

1.1 Overview ... 17

1.2 Definition and classification of obstetric anal sphincter injury (OASI) ... 17

1.3 Clinical detection of OASI... 18

1.4 Impact of OASI ... 20

1.5 OASI rates and trends ... 23

1.6 Risk factors for OASI ... 24

1.7 OASI recurrence ... 29

1.8 Quality of population health data ... 30

1.9 Perineal support ... 31

1.10 Methodological aspects ... 32

1.11 Aim and objectives ... 35

1.12 References ... 36

Chapter 2: Trends in OASIs and in risk factors ... 44 Trends in obstetric anal sphincter injuries and associated risk factors for vaginal

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vaginal birth modes for primiparous women

Chapter 4: OASI Recurrence...66

The impact of first birth obstetric anal sphincter injury on the subsequent birth: a population-based linkage study Chapter 5: The effect of using different population datasets ... 76

Ascertainment of severe perineal trauma and associated risk factors using birth data compared to linked hospital data Chapter 6: ‘Hands on’, ‘hands poised’ or ‘hands off’ the perineum ... 90

Perineal management techniques among midwives at five hospitals in New South Wales – a cross-sectional survey Chapter 7: Summary and recommendations for further research ... 113

7.1 Main findings ... 114

7.2 Strengths and limitations... 119

7.3 Recommendations for further research ... 120

7.4 Conclusion ... 123

7.5 References ... 123

Appendices Appendix 1: Addition publication ... 127

Are pregnancy outcomes associated with risk factor reporting in routinely collected perinatal data? Appendix 2: Author’s contribution and contribution of others ... 133

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ACHI: Australian classification of health interventions

aOR: Adjusted odds ratio

APDC: Admitted Patient Data Collection (also called hospital data)

ARM: Artificial rupture of membranes

CHeReL: The Centre for Health Record Linkage

CoB: Country of birth

CS: Caesarean section

ICD-10-AM: International classification of diseases, Australian modification

NSLHD: Northern Sydney Local Health District

NSW: New South Wales

OASI: Obstetric anal sphincter injury

PDC: Perinatal Data Collection (also called birth data)

PPN: Person project number

PPV: Positive predictive value

RCOG: The Royal College of Obstetricians and Gynaecologists

RCT: Randomised controlled trial

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Chapter 1:

Background

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1.1 Overview

Obstetric anal sphincter injuries (OASIs) are adverse outcomes of vaginal births involving tearing of the anal sphincter which can have short and long-term consequences for women including pain, incontinence and severe alterations to lifestyle. While consensus exists in the

identification of major risk factors, OASIs are difficult to predict for individual women.1

Reported OASIs are increasing, and without further understanding of the drivers behind these increases, prevention will remain elusive, potentially leaving more women with ongoing associated morbidity.

1.2 Definition and classification of OASI

An OASI occurs when tearing of the perineum at childbirth extends to include the anal

sphincter musculature. Traditionally, perineal tearing was classified using four levels,2 with

third and fourth degree tears collectively known as OASIs:

 First degree tear – laceration of the vaginal epithelium or perineal skin only;

 Second degree tear – first degree tear plus involvement of perineal muscles but not the

anal sphincter;

 Third degree tear – disruption of the skin, mucous membrane, perineal body and anal

sphincter muscles; or

 Fourth degree tear – third degree tear plus involvement of anal epithelium.

A revised classification system was proposed by Sultan in 1999. It differentiated between

damage to the internal and external anal sphincters (Table 1).3, 4 Its adoption was

recommended by the Royal College of Obstetricians and Gynaecologists (RCOG) in 2001,

and fully endorsed in 2007.5 Research undertaken in 2009 indicated that this classification

system had not been fully adopted in the clinical setting, with only 57% of maternity units in

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Table 1 – Revised classification of perineal injury at childbirth (endorsed by RCOG, 2007)

First degree Injury to perineal skin only

Second degree Injury to perineum involving perineal muscles but not the anal sphincter Third degree Injury to perineum involving the anal sphincter complex:

3a: Less than 50% external anal sphincter torn 3b: More than 50% external anal sphincter torn 3c: Both external and internal anal sphincters torn

Fourth degree Injury to perineum involving the external and internal anal sphincters and the anal epithelium

1.3 Clinical detection of OASI

Not all OASIs are diagnosed immediately after birth. Those that are not apparent on routine clinical examination are known as ‘occult’ injuries, and include injuries to women who have been misclassified as having a second degree tear. Prior to the RCOG endorsing the revised classification system, a survey of 672 obstetric consultants in 2002 revealed that 33% would incorrectly classify a tear to the external anal sphincter as a second degree tear.7

With the increased availability of endoanal ultrasound scanning to assess anal sphincter integrity, considerable research has been undertaken to estimate the prevalence of occult OASIs. A literature review published in 2007 included nineteen studies investigating rates of

OASI diagnosed by ultrasound but not clinically detected at birth.8 The reported vaginal rates

of occult OASIs were: 29.2% among all primiparas; 21.7% among primiparas with non-instrumental births; 32.3% among all multiparas; and 47.7% among multiparas with

instrumental births. Symptom reporting was not part of the review, and the authors state that the true clinical significance and natural history of occult OASIs are uncertain.8

The current RCOG guideline for the management of third- and fourth-degree perineal tears states:

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All women having a vaginal delivery with evidence of genital tract trauma should be examined systematically to assess the severity of damage prior to suturing. All women having an operative vaginal delivery or who have experienced perineal injury should be examined by an experienced practitioner trained in the recognition and

management of perineal tears.5 p3

A Cochrane review noted that perineal assessment immediately postpartum can be hampered

by poor lighting and lack of adequate pain relief.9 A UK guideline noted that these factors

should be addressed so that proper examination can occur, and should be conducted gently

and sensitively with full explanation provided to the woman.10

While confusion in the previous classification system may have contributed to

under-diagnosis of OASIs, further research published in 2006 demonstrated that clinical diagnostic skills also have an impact. When primiparous women were clinically re-examined by an experienced researcher immediately after birth, Andrews et al revealed that 87% of OASIs

had not been identified by midwives and 27% not identified by doctors.11 This translated to a

reported OASI rate by clinicians of 11%, compared with 24.5% by the researcher. This research indicated many ‘occult’ OASIs were in fact identifiable clinically but were being missed. Undetected OASI may result in inappropriate repair not addressing the anal sphincter

defect, which has clinical, epidemiological and medico-legal implications.4

It is of note that while the researcher in Andrews’ study routinely performed a rectal

examination as part of his assessment for each woman, none of the midwives carried out this

assessment.11 The independent influence of this practice on the detection rate is not known,

but is stressed as important by the authors and is in keeping with their prior recommendation that ‘every woman who has an episiotomy or sustains a perineal tear should have a rectal

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examination to exclude rectal or anal sphincter injury’.12 p189, 13 This is necessary because

disruption to the anal sphincter muscle can exist beneath apparently intact perineal skin.14

While the majority of older midwifery and obstetric textbooks recommend a rectal

examination after perineal repair, very few indicate the need prior to repair.11 More recent

practice guidelines in Australia and internationally now include this recommendation, stating

that systematic assessment of genital trauma at birth should include a rectal examination.10, 15

This has been reported as routine practice in the Netherlands,16 but uptake of this practice is

not known for New South Wales.

Repair should occur immediately after birth.10 This was further highlighted by Andrews who

stated that for a woman with a persisting internal anal sphincter injury (due either to non-diagnosis or a poor repair at delivery) she ‘has lost her chance of successful repair as

colorectal experts are of the view that it is almost impossible to perform a secondary repair’.17

p197

1.4 Impact of OASI

A woman with an OASI may experience symptoms which can lead to profound physical, sexual, social, psychological changes in her life.18-21 One of the most distressing

consequences of OASI is anal incontinence (defined as the involuntary passage of flatus, or liquid or solid stool22). The internal anal sphincter runs longitudinally to the anal canal and is composed of smooth muscle under involuntary control, and is largely responsible for passive anal continence; while the external anal sphincter is a striated muscle under voluntary control encircling the anal canal.23 p644, 24 Damage to either can potentially lead to anal incontinence.

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The reported prevalence of anal incontinence as a consequence of OASI varies widely. A summary of 20 studies between 1992 to 2000 reported anal incontinence rates from 15% to

59% following primary OASI repair.22 A more recent systematic review of 31 prospective

cohort studies from 1996 to 2009 reported that of all obstetric factors, the only one associated

with faecal or flatus incontinence was a history of OASI.25 Follow-up for these studies ranged

from three months to ten years. For women with symptoms at early follow-up after repair, there is evidence that when reassessed at three years the majority will have significantly

improved.26 However, some women with a history of OASI repair who are initially

asymptomatic can develop incontinence months or years later,26, 27 while for others

symptoms of anal incontinence may not become evident until the perimenopausal years.22

It has also been postulated that anal incontinence occurring in women with a documented second degree tear reflects a number of occult OASIs, rather than true lower grade perineal injuries.14

The impact of anal incontinence can be catastrophic, affecting women physically as well as

psychosocially.28 A qualitative study graphically reported the realities these women face.

They include anxiety about the inability to control bodily functions, the need to conceal leakage with constant planning when negotiating social situations, the fear of exercise and

swimming, reduced intimacy and the ensuing loneliness with social isolation.19

Apart from the impact to the individual woman and her family, there is a considerable public

health burden with substantial health costs associated with ongoing anal incontinence.29, 30

While too far into the future to be in the minds of today’s birthing population, anal

incontinence was reported to be the most common reason for nursing home admission in the

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within developed countries, OASIs have the potential to exert influences decades after their occurrence.

Pain is generally reported as an issue for women following OASI both in the short and long-term.28, 31-33 It may adversely affect maternal and infant bonding and ability to breastfeed,34 as well as impact on sexual functioning with resulting dyspareunia.21, 35, 36

Complications following OASI repair can include infection and wound breakdown, and have

been reported in 5.0%–7.3% of women in tertiary care institutions in the US.37, 38 Some of

these women required readmission to hospital for secondary repair or other operative

interventions. Poor healing of an OASI can result in a recto-vaginal fistula. Occurring in less

than one in 1,000 vaginal births, they are rare occurrences in the developed world.39 Among

women with a fourth degree tear their incidence has been reported by studies undertaken

prior to 2000 as 0.4% to 3.0%.40

The reported morbidity associated with OASI depends on many factors including accurate clinical classification at the time of birth, the severity of the injury, the technique and materials used for suturing, the skill and education of the person performing the suturing procedure, and the length of time since birth.17, 26, 28, 41, 42 Studies which examine the impacts of OASI reflect these differences. They can also differ widely in their design, setting,

categorisation of perineal status groups for comparison, methods of outcome assessment, length of follow-up, reporting of type of surgical repair and selection of samples. This heterogeneity makes synthesis of results challenging, with some studies reporting contradictory findings to others.

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While outcomes following OASI are not the focus of this thesis, the physical, psychological and societal burden demonstrate the importance of understanding the drivers for OASIs.

1.5 OASI rates and trends Rates

Without sampling bias, data sourced from whole populations are useful in determining OASI rates that reflect the total burden. Recent international published population-based OASI rates among all vaginal births are mainly limited to Scandinavian data, with rates of 1.0% for

Finland, 2.1% for Norway, 3.3% for Sweden and 3.7% for Iceland during 2012.43 Population

data for all vaginal births are also available for NSW, and reflect a rate of 2.9% for the same

time period which is comparable to most Scandinavian rates.44 This equates to 1,985 NSW

women diagnosed with OASI during 2012.

Population data from other countries often reflect different subsets of the population and hence use different denominators; for example, among only primiparous women or among instrumental/non-instrumental births. The reported OASI rates for these countries reflect a wide variability. The Organisation for Economic Co-operation and Development (OECD) reported a range of rates among non-instrumental births during 2011 from 0.1% in Poland to 3.7% in Switzerland; with an Australian rate of 2.2%. Among instrumental births, the rates

varied from 0.5% in Poland, 7.3% in Australia and 17.3% in Denmark.45

Many OASI rates are calculated from sampled data which are prone to bias, can be very setting-specific and less generalisable, and depend on the study design. As a result, there is wide variation in the reporting of OASI rates when reported from sampled data, with

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women in a single hospital in the US where midline rather than mediolateral episiotomies

were performed.47

Trends

While rates differ from setting to setting, there is a fairly consistent pattern of an increasing trend for OASI occurrence. For example, rates sourced from population data have increased

in Finland from 0.3% in 1997 to 1.0% in 2012;43, 48 and in Wales from 1.8% in 1999 to 5.6%

in 2009.49 Reporting for the subgroup of primiparous women show increases in Sweden from

3.4% in 1994 to 5.2% in 2004;50 and in England from 1.8% in 2000 to 5.9% in 2012.51 These

rates reflect yearly relative percentage increases of 8% (Finland) to 19% (Wales); and among primiparas, 5% (Sweden) to 17% (England). With reported population rates for OASI in

NSW rising from 0.9% in 199652 to 2.9% in 2012,44 the relative percentage yearly increase of

11% is within the range reported by other countries.

Comparison over time needs to be interpreted cautiously with an understanding of associated documentation, data collections, the clinical setting and culture, clinical diagnosis and care, risk factor prevalences and demographics of the populations under study. The characteristics of birthing women and of the health systems and professionals who care for them will impact on the rates of OASI. For example, caesarean section rates differ according to time and place, and therefore the characteristics of the pool of women birthing vaginally are likely to vary. In

NSW the proportion of women birthing vaginally has fallen from 83.9% in 199052 to 68.8%

in 2012.44

1.6 Risk factors for OASI

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frequency), and these can serve to alert researchers and clinicians to practices that may be driving up OASI rates. Other factors, such as ethnicity and age, are not modifiable. The use of raw rates as a form of benchmarking for care has been criticised as it may lead to

erroneous judgement about quality.53 To determine if increases in OASI rates are in fact a

reflection of quality of care, or if they are a result of a higher risk environment which may or may not be modifiable, population differences need to be considered. These differences can be across years within the same setting (if trends over time are being examined), or across different settings (if comparisons are being made by location).

Identification of risk factors depends on their accurate reporting as well as accurate reporting of OASI, both of which are subject to a range of influences. The availability of risk factors for inclusion in analyses varies across settings. The combination of available risk factors is likely to affect the strength of different risk estimates. Despite some disparity in reporting, there is overwhelming agreement that certain characteristics are associated with an increased incidence of OASI, while the results for other factors are inconsistent.

Maternal, infant and labour factors

Maternal factors that are most consistently reported as being independently associated with OASI include primiparity54-66 and Asian ethnicity, 51, 58, 60, 65-74 while higher maternal weight is associated with fewer OASIs.54, 73, 75, 76 Infant risk factors include high birthweight50, 51, 54, 56-58, 62, 65-67, 69, 71-74, 77-81 and larger head circumference.58, 79, 82-85 While their prevalence rates will affect OASI rates, these factors are non-modifiable. The majority of studies also report

the following aspects of labour as independently associated with OASI: shoulder dystocia,51,

64-66, 70, 72, 79 increased length of second stage of labour86-89 and persistent occipito-posterior presentation of the fetal head at birth.60, 62, 79, 90-93

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For other factors, the association is not so clear. While multiparous women on the whole have a significantly decreased risk of OASI, those with only previous caesarean births have been found to be either at the same risk as primiparous women47, 66 or at increased risk.58 Male infant has been reported as a risk by one author,94 but not by others.60, 61 Increasing maternal

age tends to be reported as a risk factor; however, results depend on whether it is modelled as

a continuous or categorical variable.56, 58, 72 The risk of associated medical conditions have

not had much focus, but there is evidence that hypertension54 and gestational or maternal

diabetes58, 66, 70, 95 do carry an increased risk.

Clinical interventions

There is overwhelming evidence that among the potentially modifiable clinical interventions, instrumental birth is an independent risk factor,50, 54, 56, 58-61, 64-66, 69, 70, 72, 74, 79, 96, 97 with forceps posing a higher risk than vacuum extraction.51, 55, 56, 58, 64, 65, 69, 72, 96-100 Other interventions that have ambiguous association with OASI include epidural analgesia and induction. They were found to be associated with higher rates of OASI in a meta-analysis of 22 studies;80 however, among other studies reporting adjusted risk, epidural55, 61, 65, 101, 102 and induction 55, 66, 73, 74, 79 have been reported as non-significant.

The most complex picture emerges with use of episiotomy. Traditionally, it was believed that episiotomy reduced the likelihood of severe tearing, and it was often incorporated into routine practice. However, a Cochrane review of randomised controlled trials (RCTs) concluded that restrictive episiotomy, performed only for clinical need, resulted in less severe perineal

trauma than routine episiotomy.103 Restrictive use of episiotomy is now the usual practice in

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assessed by the accoucheur’s own criteria, with differences noted between doctors and

midwives, and within members of each profession.104

Episiotomy can be performed using a midline, mediolateral or lateral incision. The midline

approach poses higher risk for OASI;105 however, not all studies clarify the approach taken.

Mediolateral approaches are usually performed in NSW. Adding further complexity is the fact that a mediolateral episiotomy can be performed in a variety of ways, with differences in

angle and length of incision.106-108 OASI likelihood is reduced when a mediolateral

episiotomy is performed with a greater angle from the midline.109

A meta-analysis of 15 observational studies concluded that episiotomy was performed significantly more often among women with OASI; however , on sub-analysis mediolateral

episiotomy was not significantly associated with OASI.80 Other recent observational studies

not included in the meta-analysis have also concluded that the impact of an episiotomy differs between instrumental and non-instrumental births. Among instrumental births, it is reported as protective;51, 62, 63, 72, 79 but among non-instrumental births the association is less clear with reports of association with risk59, protection,51 or no significant association.79 Recent studies from Scandinavian countries report that settings and epochs with a higher episiotomy rate have lower rates of OASI.96, 110, 111.

Prior to 2013, investigation into risk factors for OASI among NSW women was limited to a single site study of approximately six and a half thousand women who gave birth during

1998–2000;102 and an investigation into risk for Asian women undertaken as a secondary

analysis of a RCT among 700 women who gave birth during 1997–2004.68 No

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ambiguity around the OASI associations of particular practices, such as epidural and

induction, there was no evidence regarding the risk of these interventions for NSW women. It is hypothesised that changes in risk factor prevalences might be at least partially implicated in the rising OASI rates. The OASI rates, risk factors, changes in prevalence of risk factors and the effect of any prevalence changes are investigated in this thesis (Chapter 2).

While there is overwhelming international evidence that instrumental births carry more risk than non-instrumental births, with forceps more strongly associated with OASI than vacuum births, the effect of episiotomy within different birth modes is less clear. Among the NSW population of women having vaginal births, there has been a fairly stable proportion of forceps deliveries from 5.7% in 2000 to 6.2% 2012, and an increase in vacuums extractions

from 7.9% in 2000 to 10.3% in 2012.44, 112 It is not known if OASI rates are rising at equal

rates within different birth modes, with and without episiotomy. This is explored as part of this thesis (Chapter 3).

Birthing and midwifery practices

There are inconsistencies in results when reviewing studies investigating maternal positions during birth and OASI risk. A review of RCTs concluded no significant difference between

upright or lateral positions compared with lithotomy or supine positions;113 however, other

studies reported squatting or kneeling in all fours position as adopted by the woman as her preference had a protective effect.114, 115

One area of practice that has changed over the past decade is an increase in waterbirths, with

the NSW Ministry of Health promoting the uptake of water immersion for labour and birth.116

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the relationship between waterbirth and severe perineal laceration was unclear, with inconsistencies across studies.117

Midwifery techniques have also been investigated in RCTs. The application of hot packs to

the perineum during the second stage of labour demonstrated protection from OASI,118 while

prolonged protracted valsalva style pushing (as encouraged by the accoucheur) was

associated with risk.67, 119 A Cochrane review of four studies reported no significant

association with antenatal perineal massage and OASI.120

There is evidence that perineal support practices used at childbirth have changed over the years. Perineal support practices are described in detail in section 1.9 (see also Chapter 6).

1.7 OASI recurrence

With OASI rates rising, the number of women at risk of an OASI recurrence in a subsequent birth is in turn increasing. Women with a history of OASI are understandably apprehensive

about further births, and some women report wishing to delay another pregnancy.21, 121, 122

Women who have had an OASI are more likely to have a planned caesarean section for any

subsequent birth.123, 124 Some researchers advocate routine caesareans for all women with a

history of OASI (even if asymptomatic for continence problems) in order to prevent anal

incontinence in the future,125 while others recommend routine caesarean for those women

with incontinence symptoms following a prior OASI.126

The reported risk of recurrence varies widely. Among different populations, there is likely variation in the proportion of women who will have a subsequent caesarean. The

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another, and different populations will also have different first birth OASI rates. Reported

recurrence rates vary from 2.0% in Israel127 to 13.4% in Ireland128 among data collected from

single site medical centres. Among population-based data, the rate was reported as 5.6% in Norway.123

Prior to embarking on this PhD, the few studies that had investigated the risk of OASI recurrence and associated factors had focussed on the birth subsequent to the one in which the OASI occurred, with no attention given to factors from the previous birth. Recurrence risk for the NSW population had not been investigated. With these gaps in knowledge, recurrence risk and associated factors from both the first and second births is explored for NSW women in this thesis (Chapter 4).

1.8 Quality of population health data

Reported OASI rates depend on the quality of the underlying data. Classification, clinical detection, documentation and subsequent coding all influence the degree to which reported rates truly represent the clinical situation. Any changes to these aspects over time will also affect reporting of trends. With the revised classification system for OASIs, surrounding publicity and publication of research showing under-diagnosis, increased awareness and improvements in detection may have occurred. These in turn may be having an effect on reported OASIs over time.

Information regarding OASI is available in the NSW Perinatal Data Collection (birth data) and in the NSW Admitted Patient Data Collection (hospital data), both of which are population-based collections and utilised for research in this thesis. A validation study has shown that OASI recording in the hospital data by the international classification of diseases

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Australian modification (ICD-10-AM) coding ‘O70.2’ (third degree perineal laceration during delivery) or ‘O70.3’ (fourth degree perineal laceration), or by the Australian

classification of health interventions (ACHI) procedure coding ‘16573-00’ (suture of third or fourth degree tear of the perineum) has a sensitivity of 94.2% and a positive predictive value (PPV) of 99.7% when compared to the medical record (considered as the ‘gold standard’). In other words, 94.2% of OASIs recorded in the medical records were recorded in the hospital data; and of the OASIs recorded in the hospital data, 99.7% were correctly recorded

according to the medical records.129 In contrast, the birth data, with a sensitivity of 81.8% and

a PPV of 75.7%, is less reliable and accurate for ascertaining OASI.129 While ascertainment

of OASI by hospital data has been used in some NSW research,124, 130 other studies have used

birth data.94, 131 No studies of OASI rates over time, or of risk factor estimates, using hospital data compared with birth data have been undertaken in NSW. This comparison is explored as part of this thesis (Chapter 5).

1.9 Perineal support

There are a variety of perineal support techniques that an accoucheur can adopt when assisting at a birth. They are broadly defined as ‘hands on’ or ‘hands poised or off’ approaches. The former approach includes any of the following techniques: one hand

pressing on the baby’s head, applying flexion to control the speed of crowning, fingers of the

other hand supporting or ‘guarding’ the perineum, and/or gripping the baby’s chin.132 The

latter approach includes: having hands close to the perineum and ready to apply gentle counter pressure to the baby’s head in case of rapid crowning (‘hands poised’), or no touching of the perineum or baby’s head during birth (‘hands off’). Results from one

Cochrane meta-analysis133 of three RCTS,134-136 showed no significant difference in OASI

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poor compliance in the treatment arm, and underpowered to detect a statistical difference in OASI rates, they have been influential in current midwifery guidelines and textbooks that either approach is appropriate.10, 15, 137-139

Despite evidence from RCTs, Norwegian researchers were inspired by low OASI rates in

Finland where, unlike Norway, a ‘hands on’ approach was routine.111 They undertook a total

of four pre and post practice change studies with the aim of reducing the OASI rate. All interventions involved in-depth education, training and support programs for midwives and doctors, encouraging ‘hands on’ perineal support, as well as other strategies such as emphasis on selective mediolateral or lateral (as opposed to midline) episiotomy at the appropriate angle and length, good visualisation of the perineum at birth and communication with the

mother regarding slow pushing techniques.140-143 All four studies reported significant

decreases in OASI rates among vaginal births from 4–5% to 1–2%.

Details of perineal management practice techniques are not routinely collected in health data for NSW. While there is anecdotal reporting of a preference for the ‘hands poised or off’ approach, it is unknown how often it is used. There has been much interest in the results from Norway, with some clinicians and researchers calling for a return to more traditional ‘hands

on’ practice.144-146 Without any evidence of change in routine practice, we cannot make even

a temporal association between increases in OASI incidence and perineal practice techniques. In order to investigate this further, an investigation of midwifery practice around perineal support was undertaken as part of this thesis (Chapter 6).

1.10 Methodological aspects

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routinely collected population level data provide an unbiased source of information which is cost-effective and less resource intensive than other collection methods. Research undertaken in this thesis for Chapters 2–5 utilised longitudinally linked NSW population health data sourced from birth data and from hospital data; one dataset for 2001–2009, and another for 2001–2011 as more data became available. Record linkage across population health datasets brings together information that relates to the same individual from different data sources, thus maximising information available; while longitudinal record linkage allows all the maternities that belong to each woman to be brought together. Each woman’s reproductive history is thus available and provides information that may affect subsequent births, and enables calculation of recurrence risk for selected outcomes.

Details of birth and hospital datasets are provided in Chapters 2–5. The NSW Centre for Health Record Linkage (CHeReL) undertook record linkage between these population-based datasets. As NSW has no unique population identifiers for individuals, CHeReL used

probabilistic methods in a best practice approach that preserves individuals’ privacy.147, 148

Demographic details provided by the data custodians at the NSW Ministry of Health were used to create a unique person project number (PPN) for each individual. No health

information was supplied to CHeReL. The false positive rate for the linkage as a measure of data quality was reported by CHeReL as 0.3%. The PPNs were then sent back to the data custodians, who merged them with the health information. Personal identifying information was deleted before the data custodians sent the data to the researchers, who used the PPNs to link health data, longitudinally and cross-sectionally, from the population datasets.

The birth data collection had undergone revisions in 2006 and in 2011, and the affected variables were re-coded to make them compatible across all years. The birth data for each

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year were combined into one dataset, and hospital data then merged onto each birth record using linkage keys. Each sequential birth was identified for each woman and numbered, and any duplicate records identified and removed. For analysis in this thesis where population health data were used, published local validation studies relating to maternal health data guided the source of variable identification.129, 149, 150

Reporting of OASI rates is usually undertaken among vaginal births, and this practice has been adopted in this thesis. All rates reflect overt OASIs (those that have been diagnosed at the birth), and do not include occult injuries (those that are discovered at a later date by endoanal ultrasound).

Investigation into perineal practice was undertaken using a questionnaire to survey midwives working in Northern Sydney Local Health District during a two week period in 2014.

Multiple choice questions were used, with free text option. Midwives were asked to choose between a variety of perineal practice techniques that they would use for assisting at a low risk non-water birth, and what they would use in situations of higher risk. Demographic details, and information about which practices were taught during pre-registration training, were also collected.

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1.11 Aim and objectives Aim

The overarching aim of the research presented in this thesis is to examine the relationship between OASI rates for NSW and the associated clinical and demographic factors, as well as the impact of data source, and to quantify which perineal management approaches are used by NSW midwives.

Specific objectives

1. To ascertain the OASI rates among singleton vaginal births ≥37 weeks gestation in NSW

2001–2009; to determine risk factor effect sizes and trends; and to compare predicted with observed OASI rates (Chapter 2).

2. To determine if the rising risk of OASI is constant over time for different modes of births with and without episiotomy (Chapter 3).

3. To determine the risk factors from first and second births for OASI recurrence at second birth, and effect of first birth factors on planning for either caesarean or vaginal second birth (Chapter 4)

4. To compare OASI trends when reported by birth data versus linked hospital data, and ascertain the impact of data source on the modelling of risk factors and outcomes (Chapter 5)

5. To determine (i) which perineal protection techniques are currently preferred by

midwives in NSW for low risk non-water births; ii) if midwifery characteristics influence preference; (iii) if practice has changed from pre-registration training; and (iv) whether midwives change techniques in different clinical scenarios. (Chapter 6)

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1.12 References

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