Australia's mothers and babies

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. Poor fetal growth is associated with increased risk of stillbirth and with fetal distress during labour, and may make babies more likely to develop long-term health conditions later in life (Draper et al. 2017; Flenady et al. 2018; Sharma et al. 2016).

Adjusting birthweight for gestational age allows for differences in a baby’s growth status and maturity to be considered when examining their health at birth.

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 (for more information on Australian national birthweight percentiles see Methods).

Data on birthweight adjusted for gestational age in this report is limited to liveborn singleton babies. Birthweight for gestational age was calculated for this report using the national percentiles based on liveborn singleton babies born between 2004 and 2013. Updated birthweight percentiles based on liveborn singleton and liveborn twin babies born between 2013 and 2022 are available in tables 7.2 and 7.3 of the NPDC annual update 2023 tables. 

In 2023, 9.5% of babies were small for their gestational age. Between 2013 and 2023, the proportion of babies who were small for their gestational age remained relatively stable (between 9.1% in 2021 and 9.6% in both 2013 and 2016). 

Between 2013 and 2023, the proportion of babies who were an appropriate birthweight or large for their gestational age also remained relatively stable (between 81% and 82% and between 9.0% and 9.9%, respectively).

Figure 1 presents trend data on the birthweight adjusted for gestational age of liveborn singleton babies, by selected maternal and baby characteristics, between 2013 (or earliest available year of data) and 2023. Select the ‘Current data’ button to view 2023 data.

In 2023, babies were more likely to be small for their gestational age if they were born to:

• mothers who live in Very remote areas (13%)
• underweight mothers (19%)
• mothers aged under 20 (15%)
• mothers who smoked (17%)
• mothers who lived in the lowest socioeconomic areas (11%)
• mothers who were born in Nepal (21%), India (18%) or Pakistan (16%).

Figure 2 presents the number and proportion of liveborn singleton babies who were small for gestational age, by PHN area and SA3.

In 2023, the proportion of liveborn babies who were small for gestational age ranged from 6.7% (in Western Victoria) to 14% (in Western Sydney) across PHNs, and from 3.7% (in Caboolture Hinterland) to 18% (in Parramatta) across SA3s.