Managing your weight and gestational diabetes

Women who are overweight are at higher risk of developing gestational diabetes, although many women who develop it are not overweight at all.

Woman's feet standing on scales

Myth buster

Eating for two’ is a myth: Your baby will grow well for the first two trimesters of pregnancy without you eating any extra calories at all. During the last trimester of your pregnancy you may need up to 200 extra calories per day – a small snack.

The standard way to assess whether someone is overweight, or underweight, is through the body mass index (BMI) using your pre-pregnant or booking-in appointment weight. This is a scale that measures the ratio between your weight and your height. To find out your BMI, go to the BMI tracker here. Your BMI has to be based on your pre-pregnancy or very early pregnancy weight.

If your BMI is 30 or over you will have extra care in pregnancy as you are at greater risk of some conditions, such as high blood pressure.

"I felt more in control being able to follow the diet. I was a bit stubborn about it, but it did help."Zoe, mum of one

Most pregnant women put on some weight in pregnancy, but there is no definitive guidance about how much you should put on as every women is different. The weight includes extra blood volume, the placenta and the growing baby and womb. Do not try to lose weight by ‘dieting’ as this may not be safe for your baby. Your healthcare team will be monitoring you and baby and regularly checking your weight and discussing progress with you.

If your team feels that your weight could be an issue, you may find that they approach this by talking about what to eat, rather than weighing you during your pregnancy. This is because managing your weight when you have gestational diabetes is not about dieting or trying to lose weight. It is about making small changes to your diet and exercise to ensure that you do not gain too much weight, and managing your blood glucose levels to keep yourself and your baby healthy.

What does all this mean for you?

For some women, changing their diet is the hardest thing about having gestational diabetes. Eating our favourite foods can be very comforting, and especially during pregnancy – a time when so much is changing – it can feel very unsettling to have to make yet another change.

It is easy to feel overwhelmed as you start looking at ingredients on packets and realise how much sugar is in the foods we take for granted. But after a while you will find foods that you enjoy even if they are not your old favourites.

"My husband had to change his diet as well as me. We didn’t keep any cakes or sweets in the house!" Maria, mum of one

Changing your diet also has an effect on your relationship with those around you. Talk to your friends, partner if you have one or family, and decide together how you will do this. Other family members may be happy to join the healthy diet to support you, and to become healthier themselves. Others find a compromise, such as eating separate meals and not keeping sugary foods in the house, to help you avoid temptation. There is no right way, so find what works for you.


  1. Dornhorst, A and Banerjee, A (2010). Diabetes in Pregnancy, in Holt RIG, Cockram CS, Flyvbjerg A et al (ed.) Textbook of diabetes, 4th edition. Oxford: Wiley-Blackwell
  3. NICE (2010) Weight management before, during and after pregnancy. National Institute for Health and Clinical Excellence. Public health guidance [pdf file, accessed September 2013]
  4. Heslehurst D, Brown A (2013) Managing obesity in pregnant women: an online guide for health professionals Available at accessed 4 August 2014)
  5. RCOG (2011) Why your weight matters during pregnancy and after birth
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Read more about gestational diabetes treatment

Last reviewed on March 1st, 2015. Next review date March 1st, 2018.

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