Why should I put on weight during pregnancy?

All women should gain weight during pregnancy. Maintaining a healthy weight during pregnancy means you need to monitor you don’t gain too much weight, while ensuring that your baby receives enough energy and nutrients for healthy development.

The added weight during pregnancy results from the growing baby, the amniotic fluid and placenta which surround and protect the foetus, additional fat stores, growing breast and uterine tissue as well as an increased quantity of blood.

How much weight should I put on during pregnancy?

The amount of weight you should gain during pregnancy depends on your BMI before you fell pregnant. If your doctor did not take your weight and BMI before you fell pregnant, they will use your weight and BMI from your first antenatal care appointment (which you should do as soon as you discover you are pregnant).

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Weight gain during pregnancy

Healthy weight women (women with a BMI ≥18.5-24.99) who are pregnant can obtain sufficient energy with a healthy balanced diet. However, they will need to increase their overall food intake as the pregnancy progresses and foetal growth increases. Additional food intake is necessary to ensure they gain sufficient weight to account for their growing foetus. These women should expect to gain 11.5-16kg by the end of their pregnancy.

Women who are underweight (BMI <18.5) and those in the low end of the healthy weight range (BMI <20) are encouraged to gain weight (in additional to normal pregnancy weight gain) by eating above their energy requirements. This weight gain is associated with better foetal growth and women who are having difficulty gaining weight may benefit from professional help and advice. These women should expect to gain 12.5-18kg during pregnancy.

Overweight women (BMI ≥25) who are already pregnant should not attempt to lose weight during pregnancy. There are no demonstrated health benefits of pregnancy weight loss for these women and it may be harmful to the baby. These women should expect to gain 7-11.5kg during their pregnancy.

As being overweight or obese is associated with poor maternal and infant health outcomes, overweight women who are planning a pregnancy should ideally lose weight before they become pregnant. However obesity, like other symptoms of poor nutrition is related to health and socioeconomic inequalities, and losing weight can be a difficult process. Overweight women may benefit from professional advice while they are attempting to lose weight.

Table 1: Weight gain during pregnancy

 Pre-pregnancy BMI  Recommended Weight Gain
 BMI < 18.5  12.5 – 18.0kg
 BMI 18.5 – <25.0  11.5 – 16.0kg
 BMI 25.0 – <30.0  7.0 – 11.5kg
 BMI ≥30.0  5.0 – 9.0kg

How much weight do women gain during pregnancy?

Weight gain during pregnancyOnly 30-40% of pregnant women gain weight within the recommended ranges for their BMI (see table). Some women fail to gain enough weight during pregnancy, although in developed countries over-nutrition before and during pregnancy is more of a concern. For example, in the United States 18-38% of women are obese when they become pregnant and the majority continue to over-consume and gain excessive weight during pregnancy. In Australia, 38% of all pregnant women gain excessive weight during pregnancy, while 26% gain insufficient weight. Amongst women who are overweight when they fall pregnant, 56% gain excessive weight during pregnancy. Many women fail to lose the weight they gain during pregnancy after childbirth.

What stages of pregnancy should I gain weight?

Women gain most of their additional pregnancy weight in the second and third trimesters of pregnancy. Most women gain about 3kg in the first trimester of pregnancy and an average of 0.5kg per week after that. Weight gain drops off again after 36 weeks.

Monitoring my weight gain in pregnancy

In order to reliably monitor pregnancy weight gain, a doctor will measure both a woman’s weight and her BMI before pregnancy. Pre-pregnancy weight will enable accurate measures of weight change, while pre-pregnancy BMI will indicate how much weight a woman should gain whilst pregnant. Women should expect to be weighed and have their height measured in a preconception check-up.


More information

Pregnancy For more information about pregnancy, including preconception advice, stages of pregnancy, investigations, complications, living with pregnancy and birth, see Pregnancy.
Nutrition For more information on nutrition, including information on types and composition of food, nutrition and people, conditions related to nutrition, and diets and recipes, as well as some useful videos and tools, see Nutrition.



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