Body mass index

Obesity in pregnancy contributes to increased risks of illness and death for both mother and baby. Pregnant women who are obese have an increased risk of thromboembolism, gestational diabetes, pre-eclampsia, post-partum haemorrhage (bleeding) and wound infections. They are also more likely to deliver via caesarean section. Babies of mothers who are obese have higher rates of congenital abnormality, stillbirth and neonatal death than babies of mothers who are not obese (CMACE & RCOG 2010).

BMI is a ratio of weight and height (kg/m2). The normal range of BMI for non-pregnant women is 18.5 to 24.9. While increases in BMI are expected during pregnancy, a BMI of 30 or more at the first antenatal visit is defined as obesity in pregnancy.

Data on maternal BMI were available for mothers in all states and territories for the first time in 2016. However, data collection methods vary between jurisdictions, so care must be taken when making comparisons.

Mothers who were overweight or obese were more likely to be aged 40 or over and to give birth by caesarean section, than mothers who had a normal weight or who were underweight. The proportion of overweight or obese mothers increased with the number of previous pregnancies. Nearly 2 in 5 mothers who had 4 or more previous pregnancies were obese compared with about 1 in 5 mothers with only one previous pregnancy.