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. 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.

Adjusting birthweight for gestational age allows for differences in a baby’s growth status and maturity to be taken into account 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.

Data on birthweight adjusted for gestational age is limited to liveborn singleton babies. Australian birthweight percentiles for liveborn singleton babies are available in the data tables.

The figure shows a bar chart of the proportion of singleton liveborn babies by birthweight adjusted for gestational by a range of topics for 2019 and a line graph of topic trends from 2013 to 2019. In 2019, 9.4% or 27,564 babies were small for gestational age.

Babies were more likely to be small for gestational age if they were:

  • Indigenous (13%)
  • born to Indigenous mothers (14%)
  • born to mothers who live in Very remote areas (13%)
  • born to underweight mothers (19%)
  • born to teenage mothers (aged under 20) (13%)
  • born to mothers who smoked (17%)
  • born to mothers who lived in the lowest socioeconomic areas (11%).

The figure shows a map of the distribution small for gestational age liveborn babies by Primary Health Network area for the years 2013 to 2019.

For more information on liveborn babies who were small for gestational age by Primary Health Network area see National Perinatal Data Collection annual update data table 5.6.

For related information see National Core Maternity Indicator Small babies among births at or after 40 weeks of gestation