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Maternal and perinatal outcomes by planned place of birth in Australia 2000 – 2012: a linked population data study
  1. Caroline S E Homer1,2,
  2. Seong L Cheah1,
  3. Chris Rossiter1,
  4. Hannah G Dahlen3,
  5. David Ellwood4,
  6. Maralyn J Foureur1,
  7. Della A Forster5,6,
  8. Helen L McLachlan5,7,
  9. Jeremy J N Oats8,
  10. David Sibbritt9,
  11. Charlene Thornton10,
  12. Vanessa L Scarf1
  1. 1 Centre for Midwifery, Child and Family Health, University of Technology Sydney, Sydney, New South Wales, Australia
  2. 2 Maternal and Child Health, Burnet Institute, Melbourne, Victoria, Australia
  3. 3 School of Nursing and Midwifery, University of Western Sydney, Parramatta, New South Wales, Australia
  4. 4 School of Medicine, Griffith University, Gold Coast, Queensland, Australia
  5. 5 Judith Lumley Centre, La Trobe University, Melbourne, Victoria, Australia
  6. 6 Maternity Services, Royal Women's Hospital, Parkville, Victoria, Australia
  7. 7 School of Nursing and Midwifery, La Trobe University, Bundoora, Victoria, Australia
  8. 8 Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Victoria, Australia
  9. 9 Faculty of Health, University of Technology Sydney, Sydney, New South Wales, Australia
  10. 10 College of Nursing and Health Sciences, Flinders University Faculty of Medicine Nursing and Health Sciences, Adelaide, South Australia, Australia
  1. Correspondence to Professor Caroline S E Homer; caroline.homer{at}uts.edu.au

Abstract

Objective To compare perinatal and maternal outcomes for Australian women with uncomplicated pregnancies according to planned place of birth, that is, in hospital labour wards, birth centres or at home.

Design A population-based retrospective design, linking and analysing routinely collected electronic data. Analysis comprised χ2 tests and binary logistic regression for categorical data, yielding adjusted ORs. Continuous data were analysed using analysis of variance.

Setting All eight Australian states and territories.

Participants Women with uncomplicated pregnancies who gave birth between 2000 and 2012 to a singleton baby in cephalic presentation at between 37 and 41 completed weeks’ gestation. Of the 1 251 420 births, 1 171 703 (93.6%) were planned in hospital labour wards, 71 505 (5.7%) in birth centres and 8212 (0.7%) at home.

Main outcome measures Mode of birth, normal labour and birth, interventions and procedures during labour and birth, maternal complications, admission to special care/high dependency or intensive care units (mother or infant) and perinatal mortality (intrapartum stillbirth and neonatal death).

Results Compared with planned hospital births, the odds of normal labour and birth were over twice as high in planned birth centre births (adjusted OR (AOR) 2.72; 99% CI 2.63 to 2.81) and nearly six times as high in planned home births (AOR 5.91; 99% CI 5.15 to 6.78). There were no statistically significant differences in the proportion of intrapartum stillbirths, early or late neonatal deaths between the three planned places of birth.

Conclusions This is the first Australia-wide study to examine outcomes by planned place of birth. For healthy women in Australia having an uncomplicated pregnancy, planned births in birth centres or at home are associated with positive maternal outcomes although the number of homebirths was small overall. There were no significant differences in the perinatal mortality rate, although the absolute numbers of deaths were very small and therefore firm conclusions cannot be drawn about perinatal mortality outcomes.

  • maternal medicine
  • epidemiology
  • perinatology

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Strengths and limitations of this study

  • This retrospective study reveals the first Australia-wide evidence on the relative safety of planned birth in hospital, a birth centre and at home.

  • It analyses linked data on the outcomes for women with uncomplicated pregnancies and their infants in all eight Australian states and territories.

  • Careful data screening eliminated most causes of obstetric complexity, resulting in three cohorts with equivalent levels of risk.

  • Inconsistency between state-based datasets limited the number of confounding variables available for analysis.

  • Insufficient data on changes in planned birth place prior to labour hampered identification of intrapartum transfers and analysis of the relationship between intended and actual place of birth.

Introduction

In Australia, most births occur in hospitals (97.5% in 2015), with some variation across the eight states and territories (for example, 91% in the Australian Capital Territory to 99% in Victoria).1 Women with uncomplicated pregnancies and who are planning hospital births in the public health system receive antenatal care from hospital-based midwives and doctors, sometimes within continuity of care models and often in partnership with local general practitioners (GPs). Hospital midwives attend their labour and birth, with medical involvement as required or in line with local protocols. In the private health system (where 25% of births take place), women receive antenatal care from private obstetricians or midwives employed by obstetricians. Hospital midwives attend their labour and birth and the obstetrician attends during the labour and is usually at the birth.2 3 There are some differences across Australia in the way care is provided, especially the local guidelines and the choices available to women. The availability of different models of care varies across the country.

While most births take place in hospital labour wards or birth suites, a small proportion (1.8% nationally) take place in midwife-run birth centres.1 In Australia these birth centres are typically co-located with hospitals (similar to alongside midwifery units in other countries) although a small number of stand-alone birth centres exist.4 Birth centres typically provide midwifery continuity of care to women with uncomplicated pregnancies in a home-like environment and are well integrated into the health system.

Less than 0.3% of Australian births take place at home, ranging from 0.1% of births in New South Wales to 0.6% in the Northern Territory.1 5 Most planned home births are attended by midwives working in private practice, some of whom also attend women in birth centres and hospitals. The integration of private homebirth services varies across the country. A small number of hospitals and birth centres offer home births through the public health system.6 An evaluation of the outcomes of publicly funded models providing homebirth showed that the rate of stillbirth and early neonatal mortality was low, at 1.7 per 1000 births. However, the sample size did not have sufficient power to generate a conclusion about safety.7

We have conducted a systematic review to examine maternal and perinatal outcomes associated with planned place of birth for women with uncomplicated pregnancies in high-income countries.8 In this analysis of 28 studies from 13 countries, women who planned hospital births had significantly higher rates of perineal trauma and instrumental/caesarean birth than those who planned other birth places. Overall, there was no significant difference in the odds of intrapartum stillbirth according to place of birth (compared with planned hospital births, planned homebirth: OR=0.94; 95% CI 0.76 to 1.17; planned birth centre OR=0.66; 95% CI 0.32 to 1.34) or in early neonatal deaths (planned home birth OR=1.00; 95% CI 0.78 to 1.27; planned birth centre 0.87; 95% CI 0.29 to 2.61).

Previous Australian state-based studies into place of birth have showed variation in findings. In New South Wales (the most populous state accounting for around 30.9% of births),9 women without pregnancy complications who planned a home or birth centre birth had significantly higher proportions of normal birth than those planning hospital births (home 97.4% vs birth centre 86.0% vs hospital 73.9%). There was no significant difference in neonatal mortality although the overall sample size (n=2 58 161, including only 742 planned home births), had insufficient power for these relatively rare outcomes. In South Australia (SA) (297 192 planned hospital births and 1141 (0.38%) planned home births), another study found lower intervention rates and equivalent perinatal death rates in home births compared with hospital births. However, the odds of an intrapartum fetal death were significantly higher among planned home births (two deaths in the planned home birth group; adjusted OR (AOR) 7.42; 95% CI 1.53 to 35.87). This study included some women with recognised risk factors in the home birth group including twins.10 Large-scale studies in other countries show similar perinatal outcomes between births planned at home and in hospitals (and birth centres where these exist) with some differences for primiparous women.11–14

There is less controversy about birth centres compared with homebirth. Data from Australian birth centres indicate lower rates of maternal morbidity,15 intervention, preterm birth and low birth weight compared with hospital births for women with similar risk profiles.16 One study identified no significant differences by birth place in perinatal mortality16 and another reported lower perinatal mortality in birth centre births, although based on actual rather than intended birth place.17 A smaller hospital-based study found no significant difference in caesarean section rates between the birth centre and labour ward for women with uncomplicated pregnancies.18 Two other birth centre studies reported higher rates of spontaneous vaginal birth and lower rates of adverse infant outcomes (neonatal intensive care unit (NICU) admission, low birth weight) compared with hospital births.19 20

The safety of place of birth continues to be questioned in Australia.21 To generate evidence to assist policy makers, health practitioners and pregnant women and their families to make informed decisions about place of birth, we undertook a national study combining data from all eight Australian jurisdictions to examine the outcomes for women with uncomplicated pregnancies related to three different birth settings. This is the first national study on the comparative safety of different planned birth settings in Australia.

Aim and objectives

The study aimed to compare the perinatal and maternal outcomes for Australian women with uncomplicated pregnancies according to planned place of birth, that is, hospital labour wards, birth centres or at home. Outcomes investigated included normal labour and birth, mode of birth, interventions during labour, postpartum maternal complications and perinatal mortality and morbidity. We defined uncomplicated pregnancy as a singleton fetus in cephalic presentation between 37 and 41 completed weeks’ gestation and free of known and recorded complications. Exclusions are detailed in box 1.

Box 1

Exclusion criteria

Women were excluded if the baby was:

  • Born before 37 and after 41 completed weeks’ gestation.

  • Born before arrival for a planned birth at hospital or birth centre.

  • Diagnosed antenatally with a congenital abnormality (all International Classification of Diseases—Australian modifications (ICD-10-AM) Q codes).

Women were also excluded if they had:

  • Received no antenatal care.

  • A previous caesarean section.

  • A breech or non-vertex presentation.

  • Labour induced for any reason.

  • An elective caesarean section (pre-labour).

  • Pre-existing (essential) and/or pregnancy-related hypertension.

  • Pre-existing or gestational diabetes.

  • Antepartum haemorrhage or any other relevant pregnancy complications.

  • ICD-10-AM Diagnosis

    • O10 Pre-existing hypertension complicating pregnancy, childbirth and the puerperium.

    • O11 Pre-eclampsia superimposed on chronic hypertension.

    • O13 Gestational (pregnancy-induced) hypertension.

    • O14 Pre-eclampsia.

    • O15 Eclampsia.

    • O24 Diabetes mellitus in pregnancy.

    • O30 Multiple gestation.

    • O31.2 Continuing pregnancy after intrauterine death of one fetus or more.

    • O36.4 Maternal care for intrauterine death.

    • O42 Premature rupture of membranes.

    • O46 Antepartum haemorrhage.

    • O75.5 Delayed delivery after artificial rupture of membranes.

    • O75.7 Vaginal delivery following previous caesarean section.

    • P95 Fetal death of unspecified cause.

Methods

Study design

The study used a population-based retrospective design, linking and analysing routinely collected electronic data from multiple sources about births between 2000 and 2012 to women with uncomplicated pregnancies. We compared outcomes from three cohorts comprising women who were as comparable as possible given the available data. In Australia, homebirth and birth centre options are mostly restricted to women who meet specific criteria, that is, have an uncomplicated pregnancy and no relevant past medical or obstetric history. We therefore endeavoured to ensure that the hospital cohort shared the same characteristics, clinically if not demographically and applied the same filters on all three cohorts to increase the similarity between groups.

online supplementary file 1

Patient and public involvement

Patients and the public were not involved in the design or conduct of the study.

Data sources

All eight Australian states and territories compile electronic perinatal datasets with items on maternal characteristics, labour, birth and perinatal outcomes in the immediate postpartum period, that is, during the birth admission. However, to eliminate women with conditions that made them fall out of the uncomplicated criteria from the sample and to examine deaths and major morbidity requiring hospitalisation beyond the perinatal period, we examined additional data sources on deaths and hospital admissions 9 months before and 12 months following birth. This study used linked anonymous data on all available mothers and infants from the following sources:

  • Perinatal Data Collection (PDC)—maternal and infant data on all live births and stillbirths from 20 weeks’ gestation or >400 g birth weight.

  • Admitted Patient Data Collection (APDC)—services provided to all individuals admitted to public and private hospitals, using the International Classification of Diseases—Australian modifications22 for clinical data.

  • Registry of Births, Deaths and Marriages—all registered births and deaths;

  • Australian Bureau of Statistics (ABS)—data on deaths including primary cause of death (only for New South Wales (NSW) and Queensland).

It was not possible to obtain data from all sources for all states and territories for the full study period due to differences in data collection systems. Table footnotes indicate the scope of data for each variable. In addition, not all states and territories provided data on maternal mortality.

Definitions

The definition of uncomplicated pregnancies (those without medical or obstetric risk factors) was determined a priori by the research team. For the most part, this used the Australian College of Midwives Guidelines for Consultation and Referral23 as a basis for the description of uncomplicated pregnancies.

Planned place of birth incorporates three possible locations: home, birth centre and hospital. Homebirths are instances where women intend to give birth outside a formal health facility, usually their own home, and receive care from a registered midwife, funded through either the public or private health system or self-funded. Birth centres provide a home-like birth setting and are run by midwives. They can be located within a hospital campus (alongside unit) or in a separate area (stand-alone unit) and require transfer to the main hospital service for access to interventions such as epidural analgesia or caesarean section. Hospital births take place in the labour ward or birth suite (terms vary across the country) of either a public or private hospital, and women are attended by midwives, obstetricians and/or general practitioner obstetricians.

The timing of the decision about birth setting is critical within the birthplace literature. While women choose a birth location early in their pregnancy, clinical factors may preclude them from achieving this intention. If they develop complications, they may no longer be eligible to give birth in a birth centre or at home. These women are excluded from comparisons of outcome by birth setting if they transfer to hospital care prior to labour. Ideally, researchers should identify planned place of birth at labour onset, to ensure that all participants have a similar level of clinical complexity. All Australian data collections record intended place of birth, but the majority did not indicate intention at labour onset. Therefore, the current study analyses data on planned place of birth identified at an undetermined time in the pregnancy, as close to labour as we were able to identify. The screening process eliminated women with many of the risk factors that would have prompted antenatal transfer from a birth centre or homebirth.

Box 2 provides the definitions of the maternal and perinatal outcomes.

Box 2

Maternal and perinatal outcomes

Maternal outcomes

Normal labour and birth: defined as spontaneous labour, cephalic presentation, without epidural, spinal or general anaesthesia, forceps, vacuum extraction, episiotomy or caesarean section.

Mode of birth: caesarean section, forceps birth, vacuum extraction and normal vaginal birth (non-instrumental).

Procedures during labour and birth: episiotomy, epidural or spinal analgesia, oxytocin augmentation.

Perineal status: severe perineal trauma (third or fourth degree tear).

Postpartum complications: postpartum haemorrhage requiring a transfusion, admission to intensive care or high dependency unit for more than 48 hours and hospital readmission within 28 days.

Perinatal outcomes

Perinatal mortality: intrapartum stillbirth, early neonatal death (0–7 days), late neonatal death (8–28 days).

Perinatal complications: Admission to special care or neonatal intensive care unit for more than 48 hours and readmission to hospital within 28 days.

Data linkage

Independent data linkage units (DLU) in each state and territory matched information from the four data sources (where available), using probabilistic linkage techniques.24 25 This generated de-identified health records linking information from multiple datasets about the same individuals. This process yields the best available data on maternal and infant health status. However, it is not infallible and has estimated false positive and false negative rates of 0.5% each.26

Cross-jurisdictional data linkage was not possible, as independent DLUs had diverging protocols for maintaining patient privacy. We therefore applied to the individual data custodians for access to the linked data, through the six DLUs (data linkage for the Australian Capital Territory and the Northern Territory is provided by NSW and SA units respectively). Data were combined on relevant variables, where comparable, into a national dataset. Table 1 provides details on the datasets. Our approach to the data linkages and combining issues are detailed elsewhere.27

Table 1

Proportion of births included in sample, by state and territory

Data cleaning, screening and cohort selection

Because the data collections were developed separately in each state and territory (except ABS collections), they had different characteristics and components. In particular, several PDC and APDC variables differed in name and type by jurisdiction. Even within the same state, some variable definitions changed over the study period, with items merged or split into multiple variables over time. The researchers scrutinised definitions to ensure accurate matching between variables with different names and attributes into a standardised dataset. The variables on mode of birth and intervention are all as defined by each state or territory.

our broad request to state dlus specified data on women with singleton pregnancies and a cephalic presentation at 37 to 41 completed weeks’ gestation. datasets arrived in different formats and met our criteria to varying extents. we then applied more specific inclusion and exclusion criteria (box 1) to generate the sample.

Data analysis

Data were converted to SPSS V.24, then grouped according to women’s planned place of birth for intention to treat analysis. Descriptive statistics were generated and reported using percentages (or incidence per 1000 births for postpartum complications and perinatal outcomes).

Categorical variables were initially compared using χ2 tests. For continuous data such as maternal age and gestation week, we used univariate general linear model for analysis of variance to examine the differences between the means. ORs comparing each outcome by planned place of birth were calculated using logistic regression, adjusted for maternal age, maternal country of birth (Australia or elsewhere), gestational age and parity (dichotomised as primiparous vs multiparous) (AOR). These confounders were decided a priori based on what is known in the literature to affect outcomes. Percentages or proportions (events per 1000) were computed for the incidence of events at each birth setting. We present analysis stratified by parity (first baby vs other) for normal labour and birth and perinatal mortality.

No imputation was made to missing data. All calculations in regression and rates were computed based on non-missing data. Wherever necessary, sizes of missing data (not stated/inadequately described) on related variables were reported. The analysis reports 99% confidence intervals. The statistical significance level was set at p<0.01 to have more precision due to the large sample size.

Ethical approval requirements prevented reporting cell sizes of less than five to maintain confidentiality and so data have been redated in the tables to ensure this requirement was met. Further details on the methods is presented elsewhere.27

Results

Demographic characteristics

The sample comprised 1 251 420 births that occurred between 1 January 2000 and 31 December 2012 to women with full-term, singleton pregnancies without complications. Of these, 1 171 703 (93.6%) births were planned in hospital labour wards (referred to as ‘hospital’ births), 71 505 (5.7%) in a birth centre and 8212 (0.7%) at home.

Women planning to give birth in hospital labour wards were more likely to be younger, having their first birth (primiparous), of a shorter gestation (less than 40 weeks) or non-Australian-born than those planning birth centre or home births (table 2).

Table 2

Demographic characteristics by planned place of birth

Mode of birth, intervention and analgesia by planned place of birth

Planned birth at home or in a birth centre was associated with normal labour and birth more often than planned hospital birth. Women planning a birth centre birth were almost three times as likely (AOR 2.72, 99% CI 2.63 to 2.81) and women planning a home birth were almost six times as likely (AOR 5.91, 99% CI 5.15 to 6.78) to have a normal birth (table 3). The odds for primiparous and multiparous women were similar. Overall, the proportion of women having a normal labour and birth were high (79% to 95% across the groups).

Table 3

Normal labour and birth* by planned place of birth and parity

Women planning hospital births were more likely to experience interventions in birth. Compared with planned hospital births, births planned in other settings had significantly lower odds of: vacuum extraction (birth centre AOR 0.42; 99% CI 0.40 to 0.44 and homebirth AOR 0.18; 99% CI 0.14 to 0.24), forceps (birth centre AOR 0.54; 99% CI 0.50 to 0.58 and homebirth AOR 0.21; 99% CI 0.14 to 0.31) and intrapartum caesarean section (birth centre AOR 0.45; 99% CI 0.43 to 0.48 and homebirth AOR 0.29; 99% CI 0.24 to 0.35). Overall, the rates of interventions in the whole cohort were low with a rate of intrapartum caesarean section of only 8%.

Women who planned a birth centre or home birth were significantly more likely to have an intact perineum (birth centre AOR 1.16; 99% CI 1.14 to 1.19 and homebirth AOR 2.07; 99% CI 1.95 to 2.20) than those planning a hospital birth. Compared with planned hospital births, third or fourth degree perineal tears were less likely in planned home births (AOR 0.53; 99% CI 0.39 to 0.73) and more likely in planned birth centre births (AOR 1.17; 53% CI 1.09 to 1.25). The odds of episiotomy were much lower in both non-hospital groups (birth centre AOR 0.37; 99% CI 0.36 to 0.39 and homebirth AOR 0.13; 99% CI 0.10 to 0.15) than in planned hospital births. The odds of other interventions such as oxytocin augmentation and epidural or spinal analgesia were lower in planned birth centre or home births (table 4).

Table 4

Mode of birth, intervention rates and perineal outcomes by planned place of birth

Maternal postpartum complications

Women who planned to give birth in a birth centre were less likely to have a postpartum haemorrhage requiring a blood transfusion than women who planned hospital births (AOR 0.66; 99% CI 0.56 to 0.78). There was no significant difference in the odds for women who planned a home birth (AOR 1.08; 99% CI 0.73 to 1.60). The odds for admission to an intensive care or a high dependency unit were lower for the planned birth centre group (AOR 0.42; 99% CI 0.31 to 0.56) but no different for the planned home birth group (AOR 0.41; 99% CI 0.15 to 1.08). However, the absolute number of admissions is small (table 5). There were no significant differences between the groups in the odds of readmission to hospital within a month.

Table 5

Maternal postpartum complications by planned place of birth

Perinatal outcomes by planned place of birth

Although the planned homebirth group had higher ORs for intrapartum stillbirth and early neonatal death than the other planned places of birth, the differences were not statistically significant. Combined data on stillbirth during labour, early and late neonatal death indicate that indicate that perinatal death is no more likely to occur after planned homebirth than in hospital birth (AOR 1.55; 99% CI 0.65 to 3.69), although the absolute number of deaths was very small (9/8182). Similarly, there was no significant difference for women planning a birth centre birth (AOR 0.84; 99% CI 0.60 to 1.19). When women were stratified by parity, there were no significant differences between any of the groups in the odds of perinatal mortality.

Women who planned a birth centre birth were more likely to have their baby admitted to the NICU and/or SCU for longer than 48 hours (AOR 1.24; 99% CI 1.10 to 1.39) than women who planned hospital births. This trend was not seen in planned home births (AOR 0.63; 99% CI 0.39 to 1.01). There were no significant differences between the three groups in the odds of readmission of the baby to hospital within 28 days (table 6).

Table 6

Perinatal outcomes by planned place of birth and parity*

Discussion

This study, the first in Australia, has examined maternal and perinatal outcomes nationally by planned place of birth including all eight states and territories. Our study has demonstrated results consistent with several international studies of planned place of birth.11 12 14 Normal births were more likely for women who planned birth in birth centres or at home than in a hospital. Women who planned to give birth at home were slightly older than women planning hospital or birth centre births, but despite this, had consistently lower rates of intervention.

The unadjusted perinatal mortality ratio for planned hospital births was 0.8 per 1000 live births compared with 0.4 in planned birth centre births and 1.1 in planned home births, although the absolute risks were very small with low numbers of deaths overall. These differences by place of birth were neither statistically significant for all women nor for cohorts stratified by parity. However, the differences are more marked in primiparous women (0.8 per 1000 in planned hospital vs 1.7 per 1000 in planned homebirth) than multiparous women (0.7 per 1000 in planned hospital vs 0.8 per 1000 in planned homebirth). Given the small number of deaths in the planned homebirth group (n=9) this may be a chance finding over a long period of time (13 years). However, it is similar to the findings of the Birthplace in England study, which found a statistically significant higher odds of a composite outcome combining perinatal mortality and selected early neonatal morbidities among primiparous women planning home birth.11 This highlights the need to explain the risks to women in absolute terms, as this is likely to be more helpful in assisting decision-making.

There were two negative findings in relation to birth centre outcomes, first, a significantly higher rate of severe perineal trauma (AOR 1.17; 99% CI 1.09 to 1.25) compared with planned hospital births. Another Australian study16 and one in New Zealand also found higher rates of perineal trauma in birth centres.28 However, other research found no significant differences in perineal outcomes, for example in studies in Norway,29 30 Denmark,31 Australia32 or England.33 The higher rate of severe perineal trauma may be related to the use of birth stools, more common in Australian birth centres but less frequently in hospitals or at home. Birth stools have been linked to higher rates of severe perineal trauma compared with other birth positions or waterbirth.34 The higher rates of trauma could also be due to better case ascertainment or lower rates of episiotomy.

The study also found higher rates of infant admission to NICU/SCN for greater than 48 hours (AOR 1.24; 99% CI 1.10 to 1.39) among planned birth centre births. This is different from other research, which either found higher rates associated with planned hospital births16 28 or else no statistically significant differences in NICU admission rates from birth centres and hospital births.29 31 35 The admissions to the NICU or SCN in the current study are low in absolute terms (1 per 100 for birth centre births) but higher than planned hospital births. This requires ongoing examination to determine possible reasons and ways to reduce the rate.

Strengths and limitations

This study is the first to comprehensively examine maternal and perinatal outcomes from three birth settings across Australia. It used a population-based sample consisting of women with uncomplicated pregnancies. The large sample size was sufficient to detect differences between the three groups, although the numbers of homebirth nationally, even over this time period, were comparatively small (ie, 8212 only 0.7% of the total sample).

The context of homebirth in Australia means there are still low numbers of women choosing homebirth and hence small numbers in this population. Private practising midwives do not have access to professional indemnity insurance which means the option for women is limited although still available in some parts of the country. Some private practising midwives in some states have visiting rights to hospitals but this is not universal leading to a lack of potential lack of integration. The publicly funded home birth models are relatively few (no more than 20 services across the country) and cater for small numbers of women. The policy and professional context has not been highly supportive of homebirth which has made scaling up of public services difficult.

Women with uncomplicated pregnancies were defined consistently across all three cohorts in the dataset. However, merging linked data from multiple jurisdictions created several challenges and potential shortcomings, including missing responses, inconsistent variable definitions and limited data from some states.27 For example, Queensland’s data collection only covered 2007–2012, resulting in under-representation: 9.6% of the combined sample, compared with 20.4% of Australian births in 2012.36 The linked data sets also could not account for women who may have moved to another state or territory in the follow-up time frame. State and territory-based data collections have inconsistent variables on other potential demographic factors such as maternal education, socioeconomic status or body mass index, limiting the variables available for controlling the analysis. Further, the small cell sizes generated meant that we were not able to report some findings under the terms of ethics agreements with data custodians.

Although we eliminated unintended home births among women intending hospital or birth centre births (births before arrival), the home birth data do not always record whether or not a qualified health professional attended. Within the constraints of the data available, we have only included births attended by a health professional. Moreover, different states recorded birthplace intentions at different times. Although this means that intended birth place is not always recorded at onset of labour, the scrupulous process of data cleaning and categorising eliminated most women with risk factors which would have rendered them ineligible for birth centre or home births. Thus, the recorded birthplace intention was as close as possible to that at labour onset. However, there is a possibility that some planned birth centre/home births were erroneously classified as planned hospital births.

Some data items were collected inconsistently across the jurisdictions, for example, transfer from home to hospital after the onset of labour. This was either because the data item did not exist or because it only recorded ‘transfer’, which could have been at any time during pregnancy. Therefore, we were unable to report on intrapartum transfer rates.

Inconsistencies in the data from different jurisdictions also affected the data analysis. The regression analysis incorporated very few potential confounders, limited to those for which consistent data were available nationwide (ie, maternal age, gestational age, parity and whether born in Australia or not). Socioeconomic status is also inconsistently collected across the country, as is maternal BMI and education, so we were unable to adjust for these factors.

It is possible that there remain some residual unobservable differences in the groups. It is possible that women planning to give birth in a birth centre or at home are different from those planning a hospital birth in a number of ways, including their motivation, attitudes to intervention and approach to birth. These are not able to be measured but may impact on the findings in relation to interventions and outcomes.

Conclusion

This study provides evidence on the safety of births planned in hospital, birth centre and at home across all states and territories in Australia by comparing cohorts of women with uncomplicated pregnancies. Inconsistencies between state-based datasets as described limited the number of variables available for analysis. However, for healthy women with uncomplicated pregnancies, planned birth centre births resulted in high rates of normal labour and birth, low rates of most maternal complications and comparable perinatal mortality outcomes. Women planning home birth also had similarly positive maternal outcomes with no statistically significant differences in the rate of perinatal mortality or NICU admission. In absolute terms, the numbers of deaths were small, although the rate of perinatal mortality was higher among primiparous women who planned homebirths than their multiparous counterparts.

Acknowledgments

We acknowledge and thank the data custodians in each state and territory and the data linkage units who assisted with data collection at each jurisdictional level.

References

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Footnotes

  • Twitter @CarolineHomer, @hannahdahlen, @VScarf

  • Contributors CSEH as the lead investigator was responsible for the overall leadership of the study including the initial conception and design, grant application, ethical approval processes, leading the project, drafting the manuscript and finalising the paper. SLC was the data analyst responsible for merging the datasets from each jurisdiction, refining the datasets, developing the analysis codes and processes and conducting the statistical analysis and has provided final approval of this version. CR worked with the data analyst to support data analysis and interpretation as well as taking a key role in supporting the drafting of the manuscript and has provided final approval of this version. HGD was involved in the initial design of the study, played a key role in developing the study questions and data analytic processes, was involved in drafting the work and/or revising it critically for important intellectual content and has provided final approval of this version. DE, MJF, DAF, HLM and JJNO were involved in the initial design of the study, played a key role in developing the study questions and providing expert review, was involved in drafting the work and/or revising it critically for important intellectual content and has provided final approval of this version. DS was involved in the initial design of the study, played a key role in developing the study questions and analytic processes and providing expert statistical planning and review, was involved in drafting the work and/or revising it critically for important intellectual content and has provided final approval of this version. CT played a key role in developing the study questions and analytic plan, assisted with planning the data set merging and cleaning of the data and providing expert epidemiological review, was involved in drafting the work and/or revising it critically for important intellectual content and has provided final approval of this version. VS was the project coordinator responsible for the ethical approval processes, took a key role in coordinating the acquisition of the data from the different states and territories as well as a lead role in planning and undertaking the analysis and interpretation, was involved in drafting the work and/or revising it critically for important intellectual content and has provided final approval of this version.

  • Funding This work was supported by the National Health and Medical Research Council Australia, Grant ID 1022422 (2012–2017).

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval The study received initial ethical approval from the lead university’s Human Research Ethics Committee (HREC) (university reference number: 2012000167) and from data custodians in each state and territory. The details are provided in a Supplementary File.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement The data are not publicly available. We are not permitted to make any part of the linked data available to any party outside those named on the research team who have been granted access.

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