Small babies among births at or after 40 weeks of gestation

Birthweight for gestational age is a key indicator of infant health that is used both as an outcome measure for health and wellbeing of the mother in pregnancy and a principal determinant of a baby’s chance of prospective survival, good health, development and wellbeing (DoH 2020). For more information, see Clinical commentary.

This indicator looks at small babies born at or after 40 weeks gestation with a birthweight less than 2,750 grams.

Key findings

  • The proportion of babies born at or after 40 weeks gestation and classified as small has declined gradually from 2.1% in 2004 to 1.2% in 2020.
  • Babies born at or after 40 weeks were more likely to be classified as small if their mothers smoked during pregnancy and, in 2020, they were 2.5 times more likely to be born small among smokers than non-smokers.

The interactive data visualisation below presents data on small babies among births at or after 40 weeks gestation by selected maternal characteristics. Click the Data tables button to view the data between 2004 and 2020 and use the radio buttons to see how each characteristic has changed during this time.

Small babies among births at or after 40 weeks gestation, by State/territory of birth and all Australia, 2004 to 2020.

This chart shows the proportion of small babies among births at or after 40 weeks gestation, by state/territory of birth, 2004 to 2020.  Data can be viewed for each state/territory of birth, and for all Australia. The proportion of small babies among births at or after 40 weeks gestation, for all Australia, showed a decreasing trend from 2.1% in 2004 to 1.2% in 2020.

Clinical commentary

Babies born at or after 40 completed weeks of gestation (280 or more days after the first day of the last menstrual period) with a birthweight less than 2,750 grams are considered small for gestational age and are likely to have been affected by intrauterine growth restriction (AIHW 2022). Poor fetal growth is associated with increased risks of fetal death and compromise in labour. Late fetal growth restriction may predispose the baby to hypertension and diabetes in adulthood (Draper et al. 2017; Flenady et al. 2018; Sharma et al. 2016).

Some babies whose intrauterine growth is normal are small, and female babies are normally smaller than male babies of the same gestational age. Use of sex-specific birthweight cut-off points would align this indicator more closely with growth restriction.

Notes

For this indicator, small babies at or after 40 weeks gestation is defined as a birthweight less than 2,750 grams; the definition of low birthweight (grams) may be different in other national or international reporting indicators. 

Indicator specifications and data

Excel source data tables are available from the Data tab.

For more information refer to Specifications and notes for analysis in the technical notes.