It’s normal to gradually gain weight during your pregnancy as your baby grows.

As your baby grows, it’s normal to gain weight during your pregnancy.

While most women gain between 11.5 kg and 16 kg, how much weight you gain is influenced by:

• your weight before you were pregnant - if you’re underweight you may need to gain a little more, and if you’re overweight you should gain a little less
• if you’re carrying twins
• if you have morning sickness.

It’s important to eat well when you’re pregnant to give your baby a healthy start. But you don’t have to ‘eat for two’, as some well-meaning people may have suggested.

Talk to your doctor about what’s the best weight gain for you.

Why am I gaining weight?

Not only is your baby growing, but your body is also developing extra body tissue - including larger breasts and uterus – the placenta, and extra blood and fluid.

Is there a ‘normal’ weight gain?

For most women, the weight gained during pregnancy is linked to their pre-pregnancy ‘body mass index’ or BMI. The formula for calculating BMI is:

Your pre-pregnancy weight (in kilograms) divided by the square of your height (in metres).

So if you weighed 68 kg and you’re 170 cm tall, your BMI calculation would be 68 / 1.7 x 1.7 = 23.5.

You can use the healthdirect BMI calculator to work out your pre-pregnancy BMI.

If you are in the healthy weight range before becoming pregnant (BMI 18.5-24.9), then ideally you should gain between 11.5 kg and 16 kg: 1-1.5 kg in the first three months then 1.5-2 kg each month until you give birth.

If you are above the healthy weight range, you should gain less. If you are below the healthy weight range, you should gain more.

Managing your weight gain

You can help put on the right amount of weight by:

• eating a healthy, nutritious diet that includes fresh fruit and vegetables, wholegrain breads and cereals, legumes, lean meat, fish and low-fat dairy products
• getting some regular moderate exercise
• avoiding fatty and sugary foods and drinks.

Make sure you know which foods are safe to eat during your pregnancy.

You’ll probably find you don’t need to consume too many extra kilojoules in the first three months. But, as your baby grows, an extra 1,400 to 1,900 kilojoules a day in the second and third trimesters is likely to provide a healthy weight gain. It’s best to add that extra kilojoules through healthy food.

You should check that your diet contains the nutrients that keep you healthy and that will give your baby a healthy start such as folic acid, iron, calcium, iodine and protein.

Keeping up your fluid intake is also important - it’s recommended you drink about two litres of water each day. Morning sickness can make you dehydrated, so talk to your doctor or health professional if you’re not retaining enough fluids.

Unless your doctor advises otherwise, you can start or continue with regular exercise when you’re pregnant as long as you adjust your activity to suit your stage of pregnancy. About 30 minutes each day of walking, swimming or pregnancy exercise classes will help - but don’t do more than 20 minutes of fast physical activity at a time, to avoid overheating.

Gaining less or more weight than is recommended can have health implications for you and your baby, such as too much weight gain increasing the risk of gestational diabetes. If you have concerns about how much weight you are gaining (or not) in your pregnancy, discuss this with your doctor or midwife.

Sources: Cochrane Library (Diet or exercise, or both, for preventing excessive weight gain in pregnancy) , , Eat for Health (Healthy eating when you’re pregnant or breastfeeding) , Jean Hailes for Women’s Health(Pregnancy and weight) , Mayo Clinic (Pregnancy weight gain: What’s healthy?) Nutrition Australia (Physical activity during pregnancy) , SA Health (Healthy weight during pregnancy)