Birthweight adjusted for gestational age
A baby may be small due to being born early (pre-term) or be small for gestational age, which indicates a possible growth restriction within the uterus.
Babies are defined as being small for gestational age if their birthweight is below the 10th percentile for their gestational age and sex, and babies are defined as large for gestational age if their birthweight is above the 90th percentile for their gestational age and sex, as determined by national percentiles (calculated through analysis of the National Perinatal Data Collection data for the period 2004 to 2013).
For more information on birthweight adjusted for gestational age, see Birthweight adjusted for gestational age in Australia's mothers and babies and Methods.
Research suggests that there is no relationship between COVID-19 infection during pregnancy and the risk of giving birth to a baby that is small for gestational age (Smith et al. 2023; Villar et al. 2021).
Figure 29 presents data on birthweight adjusted for gestational age.
Figure 29: Proportion of liveborn singleton births, by birthweight adjusted for gestational age and state and territory of birth, 2015 to 2021
Line graph live births by birthweight adjusted gestational age by state and territory of birth between 2015 and 2021.
Between 2015 and 2019, the proportion of liveborn singleton babies who were small for their gestational age has remained stable across Australia (9.4% in 2015 and 2019). Modelling showed that there was no annual change. The observed proportion of liveborn singleton babies who were small for their gestational age was 9.3% in 2020 and 9.1% in 2021, which was similar to the predicted proportions based on the modelling (9.4% in 2020 and 9.4% in 2021).
Data for modelling exclude 'Not stated' data and therefore may not match the proportions presented in the data visualisation above. For more information on modelling the trend over time, see Methods.
Babies of mothers who lived in some geographical locations were more likely to be small for gestational age. Explore the map below (Figure 30) to view data on the number and proportion of babies who were small for gestational age by PHN, remoteness and SA3.
Figure 30: Proportion of small for gestational age births, by selected geography, 2017 to 2021
Map shows proportion of small for gestational age births by selected geographies and years.
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