Questions about weight in pregnancy

Your questions about how being an unhealthy weight effects your pregnancy.

Weighing scales drawn in chalk on a black board.

Why is my weight important to my pregnancy?

If your weight is outside the ‘healthy weight’ range of the BMI scale you and your baby have an increased risk of pregnancy problems.

Having a BMI over 30 can put you at increased risk of pregnancy complications, such as gestational diabetes and pre-eclampsia, as well as creating possible health problems for your baby, including extra risk of stillbirth.

If you are underweight, this can bring a small extra risk of pregnancy complications such as miscarriagepremature birth or having an underweight baby.  

If your BMI indicates that you may be overweight or underweight, the midwifery team and your doctor will support you and give you extra care in pregnancy to check for some of these increased risks and to help you have as healthy a pregnancy as possible.

How much extra should I eat in pregnancy?

Your baby will grow and develop normally without you needing any extra food until the last three months of your pregnancy. Even then, most women only need around 200 extra calories a day, which is around half a sandwich. The most important thing is to make sure you eat a healthy, balanced diet, which will help make sure you and your baby have all the nutrients you need.

Don't let well-meaning family and friends persuade you to 'eat for two', particularly if it means more sweet foods instead of healthy food. Ask them to support you in staying healthy. Don’t have extra helpings when you’re already full and explain that you're trying to keep foods that are high in sugar or fat, such as sweets, crisps and biscuits, as occasional treats.

If your BMI shows that you are underweight or overweight then you may be at extra risk of pregnancy complications. Your healthcare team will support and advise you.

What exactly is a 'portion'?

It's not just what you eat that's important, it's how much you have of it. A fruit portion would be one apple or two plums. A vegetable portion would be a small side salad. Three heaped tablespoonfuls of cooked vegetables also count as a portion (potatoes don't count as one of your five a day as they are a starchy food). You should only take one of your fruit portions from fruit juice as it doesn’t contain all of the goodness of whole fruit and it is high in natural sugar. Choose pure juice rather than a ‘juice drink’ as these are diluted and sweetened juice. Find out more about portion size.

Is it safe to diet during pregnancy?

Pregnancy is definitely not the time for a weight-loss diet. It is a time to eat well for both you and your baby. If you try to lose weight, you and your baby may miss out on nutrients that you need to stay healthy and strong.

If you are concerned about weight, remember that if your diet is healthy much of what you put on you put on will be lost with the birth of your baby and the placenta.

Instead of worrying about putting on weight, focus on being as healthy as you possibly can and aim to have a balance of different foods from the Eatwell plate. This will help keep you healthy and prevent too much weight gain.

If you have checked your BMI and you are classed as obese, talk to your doctor or midwife. You could ask for a referral to a dietitian or ask what weight-management programmes are available for pregnant women in your area.

It's also important to stay active during your pregnancy, as this will boost your health and your unborn baby's, as well as helping with managing your weight.

Read more about fruit and vegetable portions on the NHS 5 A Day website 

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  1. Villamore E and Cnattingius S. (2006) Interpregnancy weight change and risk of adverse pregnancy outcomes: a population-based study The Lancet, 2006, 1164. 368(9542):1164-70
  2. Han Z, Mulla, S et al (2010) Maternal underweight and the risk of preterm birth and low birth weight: a systematic review and meta-analyses, International journal of Epidemiology
  3. NICE (2010)  Dietary interventions and physical activity interventions for weight management before, during and after pregnancy, Public health guidance 27, 2010
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Last reviewed on February 1st, 2015. Next review date February 1st, 2018.

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