Weight gain during pregnancy

By Annemarie Aburrow RD

Coming to terms with weight gain in pregnancy and the lack of control this may bring can be a worrying time for some mums-to-be. For others, pregnancy can be seen as an excuse to eat what they want to, or 'eat for two'. However, gaining the right amount of weight is very important for the health of both you and your baby. This guide will help you determine how much weight you should be gaining, and debunk some of the myths you may have heard.

How much weight should I gain?

Most women put on between 8kg and 14kg. The majority of this is put on after week 20, and weight gain slows down around week 35. Although there are no official evidence-based UK guidelines for appropriate weight gain, American guidelines are generally accepted. In fact, the UK National Institute for Health and Clinical Excellence (NICE) recognise and quote these ranges in their guidelines for weight management before, during and after pregnancy (2010).

To identify how much weight you should be gaining during your pregnancy, you need to work out your pre-pregnancy body mass index (BMI). This will tell you whether you were a healthy weight or not at the start of your pregnancy. To work out your pre-pregnancy BMI, simply divide the square of your height (in metres) by your pre-pregnancy weight (in kilograms). The NHS Choices website features a BMI calculator. Once you've worked yours out, use the guide below to see how much weight you should gain:

  • Healthy pre-pregnancy weight (BMI between 18.5 and 24.9)
    You should aim to put on 11.5-16 kg (25-35 lb).

  • Overweight pre-pregnancy (BMI of 25 – 29.9)
    You should aim to gain 7-11.5 kg – around 1 ½ stone would be great. Your body will use some of the excess fat stores you already have to ensure you have a healthy pregnancy.

  • Obese pre-pregnancy (BMI of 30 or more)
    You should only put on 5-9kg – around a stone would be perfect. You don't need to gain more than this, because your body will use the excess fat stores you already have to ensure the healthy development of your baby.

  • Underweight pre-pregnancy (BMI less than 18.5)
    There are no accepted figures for women who were underweight at the start of their pregnancy. Aim to put on at least 11.5kg, but don't be alarmed if you put on up to 3 stone during your pregnancy. If you don't put on enough weight, you could be at risk of having a low birth-weight baby. Speak to your midwife if you are concerned.

  • The low-down on where the extra weight goes

    Baby 3-3.5kg
    Placenta 0.5-1kg
    Amniotic fluid 1kg
    Enlarged uterus 1kg
    Increased breast tissue 1kg
    Increased blood volume 1.5kg
    Mum's fat stores 3.5kg

    Pregnancy fat stores

    Gaining weight and increasing your fat stores is a normal part of a healthy pregnancy. Extra fat is laid down to help you get through the marathon of giving birth, and for breastfeeding.

    Once you've had your baby, you will lose the weight from the baby, placenta and amniotic fluid straight away. Over the first few days and weeks, your uterus quickly contracts down and you lose the additional blood supply. Fat stores will take longer to disappear. If you're breastfeeding, these fat stores will gradually reduce with time. If you're not breastfeeding, you may need to work a little harder to lose your pregnancy weight once you're ready to think about getting back into shape.

    If you've put on more weight than is recommended, the chances are that this excess weight will be excess fat, and you may find it harder to lose this weight. Remember that it's best to wait until your 6 week check before embarking on a weight loss regime.

    Should I be eating for two?

    'Eating for two' during pregnancy a myth. During pregnancy your body becomes super efficient at absorbing nutrients from your diet, meaning your baby can get the nutrients it needs without you eating more calories in the first 28 weeks.

    During the last trimester, need an extra 200 kcal a day, which is much less than people think – 200kcal is the amount of calories in 2 slices of bread or 3 custard cream biscuits. Putting on too much weight during pregnancy will make it harder to lose it later on, so it's best to be guided by your hunger. Try to ensure your snacks are healthy, e.g. fruit, veggie sticks, crackers with low fat cheese/hummus, sandwiches, cereal or yoghurts.

    What is the problem with gaining too much weight?

    Evidence suggests that women who gain weight within the recommended ranges are more likely to have better outcomes – for both mum and baby. Gaining too much weight can affect your health, especially if you were overweight or obese at the start of your pregnancy. In particular, it can increase your risks of developing gestational diabetes and pre-eclampsia. It can also increase your risk of needed assisted delivery, e.g. forceps or caesarian section. Research shows that women who gain more than 16kg are likely to be 4-9kg heavier a year after they give birth than they were before the pregnancy.

    If you were overweight or obese at the start of your pregnancy, and put on too much weight, you may find it much more difficult to lose the weight afterwards. Babies born to overweight or obese mothers have a much higher risk of being obese in childhood and adulthood. It's therefore important to try and control your weight gain to give your baby the best start in life.

    Pregnancy is not the time to go on a diet, but it's also important not to 'eat for two'! Instead, be guided by your hunger, eat healthy snacks, eat low fat dairy produce, and drink plenty of sugar-free fluids. Doing 30 minutes of moderate-intensity physical activity each day during your pregnancy will not harm your baby and will help keep your weight in check. If you're not used to exercise, begin with up to three x 15 minute sessions, and gradually build up to daily 30 minute sessions.

    What if I'm not gaining enough weight?

    Gaining too little weight may increase your risk of having your baby too early or having a baby with a low birth-weight (less than 5.5lb). However, it's important to remember than all women are different, and some naturally slim women do not put on much weight and still give birth to healthy babies.

    In need of support?

    If you're concerned about weight gain, your midwife, doctor or dietitian will be able to help you plan your diet more effectively. If you are overweight / obese or underweight, your midwife will probably discuss diet with you at your booking appointment. Use this appointment as a chance to get the information you need to help you to have the best chance of a healthy pregnancy and birth experience. If you're reading this guide and are not yet pregnant, work towards achieving a healthy pre-pregnancy weight will increase your chances of having a healthy pregnancy.



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    The information provided on this site is not meant to substitute for the advice of a qualified medical professional. Dietinpregnancy.co.uk neither assumes any legal liability nor makes any warranty or guarantee, either expressed or implied, regarding the completeness, accuracy, usefulness, or currency of this information. It is the responsibility of the reader to check for updates to the information contained on this site.