Weight Management During Pregnancy

Excess weight has become an epidemic in Australia and New Zealand, with about five out of 10 women classified as either overweight or obese. Excess weight can lead to major health problems for women and their babies.

Many clinical studies have proven that obesity is linked to serious health risks, such as heart disease, high blood pressure, diabetes, asthma, and arthritis, among others. During pregnancy, obesity puts both the mother and baby at increased risk of complications.

Many genetic, social, behavioural and educational factors are involved in the development of obesity and excess weight. This means that no single approach to weight loss will always be effective. A weight-loss program should be tailored for each woman and should involve dietary changes, exercise and counselling.

Body Mass Index

Body mass index (BMI) is a calculated number that helps to determine whether a person is underweight, normal weight, overweight or obese. It is helpful to know your BMI if you are considering becoming pregnant or in the early stages of pregnancy.

BMI is calculated using your height and pre-pregnancy or early-pregnancy weight (your later-pregnancy weight will overestimate your true BMI).

You can calculate your BMI by dividing your weight (in kilograms) by your height (in metres) squared. For example, if a non-pregnant woman weighs 90 kilograms, and she 1.6 metres tall, then her BMI is: 90kg ÷ (1.6m x 1.6m) = 35.16.

For online calculation of your BMI, go to www.nhlbisupport.com/bmi

While BMI is a helpful indicator, it is not a perfect measurement. It does not measure body fat or consider age, or account for genetic differences among some ethnic groups.

BMI and the risk of complications during pregnancy


Weight Class

Risk of complications during pregnancy

Singleton pregnancy: Total weight-gain goal during pregnancy

18.5 or less


Increased risk

12.5 – 18kg

18.5 - 24.9

Normal range/healthy weight

No increased risk

11.5 – 16kg

25 - 29.9


No increased risk

7 – 11.5kg

30 - 34.9

Obese class 1

Mildly increased risk

5 – 9kg

35.0 - 39.9

Obese class 2

Moderately increased risk

5 – 9kg

40 or more

Obese class 3

Severely increased risk

5 – 9kg


Healthy Weight Gain During Pregnancy

Your baby’s normal growth does not depend on your weight gain. Rather, it depends on your healthy diet.

If you are overweight when your pregnancy starts, choose food wisely and exercise regularly to improve your health and fitness. This will help to minimise weight gain. Adequate nutrient intake during pregnancy is important for you and your baby, and can be achieved while eating less energy-rich foods.

Further information can be found in our detailed RANZCOG pamphlet.