Maternal mortality ratio
The incidence of maternal death is expressed as the maternal mortality ratio (MMR), which is calculated using direct and indirect deaths combined, and excludes coincidental deaths.
Although the most appropriate denominator for estimating maternal mortality would be the number of women at risk (the number of pregnant or recently pregnant women), this number is not available in Australia because the number of pregnancies ending before 20 weeks’ gestation is unknown. In Australia, accurate population data are available for the number of women who gave birth to at least 1 baby (either a live birth or a stillbirth) of 20 weeks’ completed gestation or more or birthweight of 400 grams or more and are held in the AIHW’s National Perinatal Data Collection; this is the denominator number used when calculating the MMR in this report.
MMR = (Number of direct and indirect maternal deaths(a)) / (Number of women who gave birth(a)) x 100,000
(a) For a defined place and time.
Perinatal mortality rates
Calculation of stillbirth rate
The stillbirth rate is calculated as the proportion of births in a specified population which are stillbirths. This proportion is expressed in relation to all births.
Stillbirth rate = Number of stillbirths x 1,000 / Total number of births
Calculation of neonatal mortality rate
The neonatal mortality rate is calculated as the proportion of births in a specified population which are live born and subsequently die within 28 days of birth (neonatal deaths). This proportion is expressed in relation to all live births.
Neonatal mortality rate = Number of neonatal deaths x 1,000 / Number of live births
Calculation of perinatal mortality rate
The perinatal mortality rate is calculated as the proportion of births in a specified population which are stillbirths or neonatal deaths (perinatal deaths). This proportion is expressed in relation to all births.
Perinatal mortality rate = Number of perinatal deaths x 1,000 / Total number of births
Geographic data are based on the usual residence of the mother. Between 2016 to 2020, the usual residence of the mother is based on Statistical Area Level 2 (SA2) of the Australian Bureau of Statistics Australian Statistical Geography Standard Edition 2016 for all states and territories.
Indigenous Regions (IREG) were developed by the Australian Bureau of Statistics (ABS) as part of the 2016 Australian Statistical Geography Standard (ASGS). IREGs are large geographic areas which are based on the former Aboriginal and Torres Strait Islander Commission boundaries, and cover the whole of Australia without gaps or overlaps i.e. they do not cross state and territory borders. It is important to note that IREG structure does not account for the diverse Aboriginal and Torres Strait Islander communities and language groups within the geographic area (ABS 2018a).
Perinatal data at Statistical Area Level 2 (SA2) were linked to 2016 IREGS using Australian Bureau of Statistics correspondence files.
Primary Health Network
Primary Health Networks (PHNs) have been established by the Department of Health to increase the efficiency and effectiveness of medical services and improve the coordination of care for patients.
Perinatal data at Statistical Area Level 2 (SA2) were linked to 2017 PHNs using Australian Bureau of Statistics correspondence files.
The relevant proportion for each PHN was then calculated, and categories were developed based on the median, interquartile ranges and 10th and 90th percentiles for the proportions at the PHN level. The categories were then adjusted to account for natural breaks in the distribution of the data and for easier interpretation (for example, a range with a maximum of 52.1% of mothers receiving antenatal care in the first trimester would be revised to a maximum of 50%). PHNs were allocated to categories based on unrounded proportions.
This report uses the Australian Statistical Geography Standard Remoteness Structure, which groups geographic areas into six classes of Remoteness Area based on their relative access to services using the Accessibility/Remoteness Index of Australia.
The six classes are: Major cities, Inner regional, Outer regional, Remote, Very remote and Migratory, see the Australian Statistical Geography Standard (ASGS): Volume 5 – Remoteness Structure, July 2016 (ABS 2018b).
Remoteness data used in this report are derived by applying this classification to the mother’s usual area of residence in the NPDC. Remoteness area was calculated where geographic area of usual residence was provided.
The Socio-Economic Indexes for Areas (SEIFA) are measures of socioeconomic status (SES) that summarise a range of socioeconomic variables associated with disadvantage. Socioeconomic disadvantage is typically associated with low income, high unemployment and low levels of education.
The SEIFA index used in this report is the 2016 SEIFA Index of Relative Socioeconomic Disadvantage (IRSD) developed by the Australian Bureau of Statistics for use at Statistical Area Level 2.
Since the IRSD summarises only variables that indicate disadvantage, a low score indicates that an area has many low-income families, many people with little training and many people working in unskilled occupations; hence, this area may be considered disadvantaged relative to other areas. A high score implies that the area has few families with low incomes and few people with little or no training and working in unskilled occupations. These areas with high index scores may be considered less disadvantaged relative to other areas. It is important to understand that a high score reflects a relative lack of disadvantage rather than advantage and that the IRSD relates to the average disadvantage of all people living in a geographic area. It cannot be presumed to apply to all individuals living within the area.
Population-based Australian cut-offs for SEIFA quintiles have been used in this report. This method ranks the SEIFA scores for a particular geography (for example, Statistical Area Level 2) from lowest to highest, and the geographical areas are divided into 5 groups, such that approximately 20% of the population are in each group.
The most disadvantaged group is referred to as the Lowest socioeconomic status (SES) areas and the least disadvantaged group is referred to as the Highest SES areas.
See the Census of Population and Housing: Socio-Economic Indexes for Areas (SEIFA), Australia, 2016 (ABS 2018c) for further information on SEIFA.
Statistical Area Level 3
Statistical Areas Level 3 (SA3) are geographical areas built from whole Statistical Areas Level 2 (SA2) and are designed for the output of regional data. SA3s create a standard framework for the analysis of ABS data at the regional level through clustering groups of SA2s that have similar regional characteristics. Whole SA3s aggregate to form Statistical Areas Level 4 (SA4). There are 358 spatial SA3 regions covering the whole of Australia without gaps or overlaps (ABS 2018d).
Perinatal data at Statistical Area Level 2 (SA2) were linked to Statistical Area Level 3 (SA3) using Australian Bureau of Statistics correspondence files.
To maintain privacy and confidentiality of individuals, cells in the data tables are suppressed if there is a risk of disclosure of an attribute of an individual that was not already known. A cell in a table is considered identifiable if, as well as being able to identify the entity, other details are also revealed. It is AIHW policy that these cells need to be confidentialised, unless the attribute that would be disclosed is deemed to be non-sensitive in the context of the data being published.
Numbers of less than 5 have not been published (n.p.), in line with guidelines for protecting the privacy of individuals. Exceptions to this are small numbers in ‘Other’ and ‘Not stated’ categories. Consequential suppression of numbers has also been applied where required to prevent back-calculation of small numbers. However, all suppressed numbers have been included in the totals.
Per cents based on denominators of less than 100 have also been suppressed (n.p.) for reliability reasons.
Australian national birthweight percentiles by gestational age
Birthweight percentiles were calculated from data on all liveborn singleton babies born in Australia between 2004 and 2013 with a gestational age of 20–44 weeks.
Records with indeterminate sex were excluded from analysis. Records with missing or not stated data for sex, birthweight or gestational age were also excluded. Birthweight outliers were calculated and excluded using a method based on Tukey’s box and whisker plots.
Gestational age is reported in completed weeks of gestation, calculated from the first day of the last menstrual period (LMP) or estimated by prenatal and/or postnatal assessment if the LMP date was missing. Birthweight is reported to the nearest 5 grams.
Small for gestational age is defined as babies with birthweight below the 10th percentile according to the national birthweight percentiles for 2004 to 2013.
ABS (Australian Bureau of Statistics) (2018a), Australian Statistical Geography Standard (ASGS): Volume 2 – Indigenous Structure, July 2016. ABS cat. no. 1270.0.55.002. Canberra: ABS.
ABS (Australian Bureau of Statistics) (2018b), Australian Statistical Geography Standard (ASGS): Volume 5 – Remoteness Structure, July 2016. ABS cat. no. 1270.0.55.005. Canberra: ABS.
ABS (2018c), Census of Population and Housing: Socio-Economic Indexes for Areas (SEIFA), Australia, 2016. ABS cat. no. 2033.0.55.001. Canberra: ABS.
ABS (2018d), Australian Statistical Geography Standard (ASGS): Volume 1 – Main structure and Greater Capital City Statistical Areas, July 2016. ABS cat. no. 1270.0.55.001. Canberra: ABS.