Being overweight or obese when you're pregnant puts you at higher risk of pregnancy problems, which can affect both you and your baby.
What exactly is ‘overweight’/'obesity' during pregnancy?
Your weight is calculated using your Body Mass Index (BMI) , which is a calculation that works out whether you are a healthy weight for your height. For pregnant women your BMI calculation will be based on your weight before pregnancy. This is a way for the health team to know whether you are a healthy weight for your height.
People involved in your health care will describe your BMI as follows:
- 18.5 or less = underweight
- Between 18.5 and 24.9 = healthy weight
- Between 25 and 29.9 = overweight
- Over 30 = obese
At your first antenatal visit, called the 'booking-in visit', your midwife may measure your height and weigh you to work out your BMI.
Try not to be offended if anyone involved with your health care uses the words 'overweight' or 'obese' to describe your weight. A lot of women don't like these terms but nobody is judging you. The medical experts looking after you during pregnancy need to use these categories so they can make sure you have the best advice and support to help you have a healthy pregnancy. Someone who is categorised as obese, for example, will get extra advice and care.
The higher your BMI (over 25) the higher the risk that it will complicate your pregnancy. The risks are slightly raised for a woman with a BMI of 25, for example, but much higher for a woman with a BMI over 40.
If your BMI is 30 or above the risks include:
- high blood pressure and pre-eclampsia.
- pregnancy (gestational) diabetes.
- Deep Vein Thrombosis – developing a blood clot in your legs or lungs.
- stillbirth, but this risk is still low at one in 100.
- early miscarriage, the risk rises from one in five to one in four.
- macrosomia (having a baby who is too big)
- longer labour, labour being induced, emergency caesarean delivery or having problems after the birth, such as infection or heavy bleeding
If you are overweight your baby is also more likely to be overweight and develop diabetes in later life.
Because of these extra risks, you will have extra care in pregnancy. Your doctor or midwife might have asked you to have some extra tests during pregnancy to check for some of these increased risks. Examples of extra tests are having a blood test to check for gestational diabetes, having your blood pressure checked at every visit, asking you for urine samples, and having extra scans to check your baby’s growth. You might also be asked to have some injections to help prevent DVT, or to see an anaesthetist just in case you need to have an epidural or caesarean delivery.
You might be advised to have your baby in hospital rather than at home or in a midwife-led unit due to the increased risks during labour.
What is pregnancy diabetes (gestational diabetes)?
This is a kind of diabetes that women can develop during pregnancy. Diabetes is a condition where the amount of sugar in your blood becomes too high because your body can't process and use it properly.
Gestational diabetes increases the risk that your baby will be larger than normal (macrosomia), which can lead to problems during pregnancy, labour and delivery. There can also be health issues for your baby, including the risk of developing diabetes and being obese in later life.
If your BMI was over 30 before you became pregnant, you should be tested for diabetes between 24 and 28 weeks. This is recommended by NICE. If you are not offered this test please ask your healthcare team why you haven't been offered it. If your BMI is more than 40 the test might be earlier.
What is pre-eclampsia?
Pre-eclampsia is a condition that can only happen during pregnancy. It occurs when there is a problem with the placenta, the organ that links the baby's blood supply to yours. It is a set of symptoms, including high blood pressure, protein in your urine and fluid retention.
Most cases of pre-eclampsia are mild, but serious cases can become life threatening. Because of this, it's important to tell your midwife if you have:
- lots of headaches
- blurred vision, or vision that is altered in any way
- pain in the upper part of your stomach
- swelling of your hands, face or feet (oedema) that doesn't go away
Your midwife or doctor will check for signs of pre-eclampsia at all your antenatal appointments by testing your urine. If you are at extra risk of pre-eclampsia, for example, if you are over 40, have high blood pressure or if you have had pre-eclampsia before, you might need to have your antenatal appointments in a hospital and you might have to take a low dose of aspirin.
If I'm obese and pregnant is it too late to reduce these risks?
Although you are unlikely to reduce your risk of all of these problems, there are plenty of things you can do to make sure you have a healthier pregnancy. Make sure you are tested for gestational diabetes as recommended by NICE guidelines if you have a BMI of 30 or over, and have a look at the rest of this section and the healthy eating and physical activity pages for lots of ideas. You may also be referred to a dietician who can give you specialist advice about healthy eating and losing weight during pregnancy through eating more nutritious meals rather than through dieting. Dieting is not recommended in pregnancy as it may cut down on nutrients your baby needs.
- base your meals on starchy foods such as potatoes, bread, rice and pasta, choosing wholegrain where possible.
- watch the portion size of your meals and snacks and how often you eat.
- do not ‘eat for two’.
- eat a low-fat diet. Eat as little as possible of the following: fried food, drinks and sweets/biscuits high in added sugars, and other foods high in fat and sugar.
- eat fibre-rich foods such as oats, beans, lentils, grains, seeds, fruit and vegetables as well as wholegrain bread, brown rice and pasta.
- eat at least five portions of a variety of fruit and vegetables each day, instead of foods higher in fat and calories.
- always have breakfast.
You may also be given extra information about staying active in pregnancy because this will benefit you and your baby.
- make activities such as walking, cycling, swimming, low impact aerobics and gardening part of your daily life
- take the stairs instead of the lift or go for a walk at lunchtime.
- do not sit for long periods, watching television or at a computer, for example.
- exercise will not harm you or your unborn baby but, if you are new to exercise you should begin with 15 minutes of continuous exercise, three times per week, increasing gradually to 30 minute sessions every day. A good guide that you are not overdoing it is that you should still be able to have a conversation while exercising.
Take extra folic acid
If your BMI is 30 or above you should take a daily dose of 5mg of folic acid. This is more than normal and it needs to be prescribed by a doctor. If possible you should start taking this a month before you conceive until you reach your 13th week of pregnancy. But if you haven’t started taking it early, you should still take it when you realise you are pregnant until 13 weeks.
Vitamin D supplements
All pregnant women are advised to take a daily dose of 10 micrograms of vitamin D supplement. This is particularly important if your BMI is over 30 as you are at increased risk of vitamin D deficiency.
Benefits of managing your weight in pregnancy
- You'll have a more comfortable and enjoyable pregnancy.
- You're likely to be more mobile and less likely to suffer pelvic pain.
- You're less likely to suffer with skin problems.
- You have a slightly lower chance of developing pain in your pelvis.
- You'll have less weight to lose after you baby is born.
There’s no escaping it: Everyone puts on weight in pregnancy. It’s totally normal and the right thing for you and your baby. Managing your weight by eating well and keeping active is good for you and your baby.
Most types of exercise are fine even if you are overweight. Being active during your pregnancy is safe and healthy for you and your baby.
Your questions about how being an unhealthy weight effects your pregnancy.
It's important to look after yourself and start managing your weight as early as possible in your pregnancy to get the most benefit. Having some goals and planning what you're going to do will help.
Most women who get pregnant after weight-loss surgery have an uncomplicated pregnancy and birth. The risks to you and your baby are lower after surgery than if you kept a very high body mass index (BMI).
There is plenty of support available to help you manage your weight during your pregnancy and after your baby is born.
- RCOG (2011) Why your weight matters during pregnancy and after birth, Information for you, Royal College of Obstetricians and Gynaecologists
- 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.
- Heslelhurst N, Lang R, Rankin J et al. (2007) Obesity in pregnancy: a study f the impact of maternal obesity on NHS maternity services, British Journal of Obstetrics and Gynaecology, 2007 Mar;114 (3):334-42.
- NICE (2010) Dietary interventions and physical activity interventions for weight management before, during and after pregnancy, Public health guidance 27, 2010
- Oken E and Gillman M. (2003) Fetal origins of obesity Obesity Research, 2003, 11(4):496-506.
- Denison F, Norrie G, Graham B et al. Increased maternal BMI is associated with an increased risk of minor complications during pregnancy with consequent cost implications. British Journal of Obstetrics and Gynaecology, 2009 116(11):1467-72.
ℹLast reviewed on February 1st, 2015. Next review date February 1st, 2018.