Published: November 2018
Updated: August 2022
This information is for you if you are overweight and are planning to become pregnant, expecting a baby or have recently given birth.
It may also be helpful if you are a partner, relative or friend of someone who is in this situation.
Most women who are overweight have a straightforward pregnancy and birth and have healthy babies. However, being overweight or obese does increase the risk of complications to both you and your baby. You and your healthcare professionals can work together to reduce some of these risks.
A glossary of medical terms is available on the RCOG website at A-Z of medical terms.
- BMI (body mass index) calculation is a simple way to find out whether you are a healthy weight for your height. A BMI of 18.5–24.9 is considered healthy.
- A BMI of 25 or above is associated with risks for you and your baby.
- The higher your BMI, the greater the risks are.
- Some of the risks with raised BMI include increased risk of thrombosis, gestational diabetes, high blood pressure, pre-eclampsia, induction of labour, caesarean birth, anaesthetic complications and wound infections.
- A raised BMI also increases your risk of having a miscarriage, giving birth early, having a big baby or having a stillbirth.
- Healthy eating and exercise can benefit you and your baby.
- If your BMI is 30 or above, you are advised to take a higher dose of folic acid (5 mg per day).
BMI is your body mass index, which is a measure of your weight in relation to your height. A healthy BMI is in the range 18.5 to 24.9. A person with a BMI in the range 25 to 29.9 is considered overweight. A person with a BMI of 30 or above is considered to be obese.
Your BMI will be calculated at your first antenatal booking appointment.
You may be weighed again later in your pregnancy.
You can also calculate your BMI by using the calculator on the NHS website:
Most women with a high BMI have a straightforward pregnancy and have healthy babies. However, being overweight or obese does increase the risk of complications for you and your baby. The higher your BMI, the greater the risks.
If your BMI at your antenatal booking visit is 30 or above, you may be offered consultant-led antenatal care. Your healthcare professional will discuss with you any additional risks for you and your baby as well as how these can be reduced.
Thrombosis is a blood clot in your legs (venous thrombosis) or in your lungs (pulmonary embolism), which can be life-threatening. Pregnancy itself increases your risk of developing thrombosis. If you are overweight, the risk of developing thrombosis is further increased.
Your risk for thrombosis will be assessed at your first antenatal appointment and will be monitored during your pregnancy. You may be offered injections of a medication called low-molecular-weight heparin to reduce your risk of thrombosis. This is safe to take during pregnancy. For more information, see the RCOG patient information Reducing the risk of venous thrombosis in pregnancy and after birth.
Diabetes that is first diagnosed in pregnancy is known as gestational diabetes. If your BMI is 30 or above, you are three times more likely to develop gestational diabetes compared with women with a BMI under 25.
You will be offered a test for gestational diabetes between 24 and 28 weeks. If the test shows that you have gestational diabetes, you will be referred to a specialist for further testing and treatment as required.
For further information see the RCOG patient information Gestational diabetes.
High blood pressure and pre-eclampsia
Being overweight increases your risk of developing high blood pressure and pre-eclampsia. If you have a BMI of 30 or above, your risk of pre-eclampsia is 2–4 times higher compared with those with a BMI under 25.
Your blood pressure and urine will be monitored at each of your appointments. Your risk of pre-eclampsia may be further increased if:
- you are over 40 years old
- you have had pre-eclampsia in a previous pregnancy
- your blood pressure was already high before pregnancy.
If you have these or other risk factors, your healthcare professional may recommend a low dose of aspirin to reduce the risk of you developing pre-eclampsia.
For further information, see the RCOG patient information Pre-eclampsia.
Mental health problems
All pregnant women are asked some questions about their mental health at their first antenatal (booking) appointment. Being overweight slightly increases your risk of developing mental health problems in pregnancy and after birth. Your healthcare professional will ask you a few questions to help identify whether you are at risk.
Further information on mental health problems during pregnancy and after birth is available on the Best Beginnings website at: www.bestbeginnings.org.uk/helping-parents-with-mental-health-issues.
- The overall likelihood of a miscarriage in early pregnancy is 1 in 5 (20%), but if you have a BMI of 30 or above, your risk increases to 1 in 4 (25%).
- If you are overweight before pregnancy or in early pregnancy, this can affect the way your baby develops in the uterus (womb). Overall, around 1 in 1000 babies in the UK are born with neural tube defects (problems with the development of the baby’s skull and spine), but if your BMI is 30 or above, this risk is nearly doubled (2 in 1000).
- If you are overweight, you are more likely to have a baby weighing more than 4 kg, which increases the risk of complications for you and your baby during birth. If your BMI is 30 or above, your risk is doubled from 7 in 100 to 14 in 100 compared with women with a BMI of between 20 and 30.
- The overall likelihood of stillbirth in the UK is 1 in every 200 births. If you have a BMI of 30 or above, this risk increases to 1 in every 100 births.
- If you have a high BMI during pregnancy, you may need additional ultrasound scans to check your baby’s development, growth and position. Your baby’s growth is normally monitored during pregnancy using a tape measure to record the size of the uterus. If your BMI is more than 35 then it may be difficult to be accurate with a tape measure so your healthcare professional may request additional ultrasound scans.
- All women in the UK are offered an ultrasound scan at around 20 weeks to look for structural problems that your baby may have. This scan is less accurate at picking up problems if your BMI is raised.
A healthy diet will benefit both you and your baby during pregnancy and after birth. You may be referred to a dietician for specialist advice about healthy eating. The website www.nhs.uk/Livewell/healthy-eating/Pages/Healthyeating.aspx can provide more information about a healthy diet.
Trying to lose weight by dieting during pregnancy is not recommended. However, by making healthy changes to your diet, you may not gain any weight during pregnancy and you may even lose a small amount. This is not harmful.
You will be offered information and advice about being physically active during pregnancy. There is further RCOG information about physical activity for pregnant women.
Physical activity will benefit both you and your baby. If you have not previously exercised routinely, you should begin with about 15 minutes of continuous exercise, three times per week, increasing gradually to 30 minute sessions every day. Some examples of healthy exercise include swimming, walking and pregnancy yoga.
An increased dose of folic acid
Folic acid helps to reduce the risk of your baby having a neural tube defect. If your BMI is 30 or above, a daily dose of 5 mg of folic acid is recommended. This is higher than the usual pregnancy dose and is only available on prescription. Ideally, you should start taking this a month before you conceive and continue to take it until you reach your 13th week of pregnancy. However, if you have not started taking it early, there is still a benefit from taking it when you find out that you are pregnant.
There is an increased risk of complications during labour and birth, particularly if your BMI is 40 or more. These complications include:
- your baby being born before 37 weeks of pregnancy (preterm birth)
- a longer labour
- your baby’s shoulder becoming ‘stuck’ during birth (shoulder dystocia); for further information, see the RCOG patient information Shoulder dystocia.
- an emergency caesarean birth
- more complications during and after a caesarean birth, such as heavy bleeding, anaesthetic complications and wound infection.
Planning for labour and birth
While you are pregnant you should have a discussion with your healthcare professional about where you will choose to give birth. Depending on your individual circumstances, you may be advised to give birth in a consultant-led unit with easy access to medical support.
What happens in early labour?
You may be offered a cannula (a fine plastic tube that is inserted into a vein to allow drugs and/or fluid to be given directly into your bloodstream) early in labour. If you are overweight, it may be more difficult for your healthcare professional to do this, which may lead to a delay if it is not done until it is needed in an emergency situation.
All types of pain relief are available to you. However, having an epidural can be more difficult if you are overweight. You may be offered a discussion with an anaesthetist to talk about your choices for pain relief during labour.
Delivering the placenta (afterbirth)
To reduce your risk of postpartum haemorrhage (heavy bleeding after childbirth), your healthcare professional will recommend having an injection to help with the delivery of the placenta (afterbirth). For further information, see the RCOG patient information Heavy bleeding after birth (postpartum haemorrhage).
After giving birth, some of your risks continue. By working together with your healthcare professionals, you can minimise the risks in a number of ways, as discussed below.
Monitoring blood pressure
If you developed high blood pressure or pre-eclampsia during pregnancy, you are at increased risk of high blood pressure for a few weeks after the birth of your baby and this will therefore be monitored.
Prevention of thrombosis
You are at increased risk of thrombosis for a few weeks after the birth of your baby. Your risk will be reassessed after your baby is born. To reduce the risk of a blood clot developing after your baby is born:
- try to be active as soon as you feel comfortable – avoid sitting still for long periods.
- wear special compression stockings, if you have been advised you need them
- if you have a BMI of 40 or above, you may be offered blood-thinning injections (low-molecular-weight heparin treatment) for at least 10 days after the birth of your baby; it may be necessary to continue taking this for 6 weeks.
Information and support about breastfeeding
How you choose to feed your baby is a very personal decision. There are many benefits of breastfeeding for you and your baby. It is possible to breastfeed whatever your weight. Extra help is available if you need it from your healthcare professional and local breastfeeding support organisations (for example, the NCT www.nct.org.uk/baby-toddler/feeding/early-days/new-baby-feeding-support).
Healthy eating and exercise
Continue to follow the advice on healthy eating and exercise. If you want to lose weight once you have had your baby, you can discuss this with your healthcare professional.
If you have a BMI of 30 or above, whether you are planning your first pregnancy or are between pregnancies, it is advisable to lose weight. By losing weight you:
- increase your ability to become pregnant and have a healthy pregnancy
- reduce the additional risks to you and your baby during pregnancy
- reduce your risk of developing diabetes in further pregnancies and in later life
- reduce the risk of your baby being overweight or developing diabetes in later life.
If you have fertility problems, it is also advisable to lose weight. Having a BMI of 30 or above may mean that you would not be eligible for fertility treatments such as IVF under the National Health Service.
Your healthcare professional can offer you advice and support to lose weight. Crash dieting is not good for your health. Remember that even a small weight loss can give you significant benefits.
You may be offered a referral to a dietician or an appropriately trained healthcare professional. If you are not yet ready to lose weight, you should be given contact details for support for when you are ready.
RCOG patient information
- Reducing the risk of venous thrombosis in pregnancy and after birth
- Gestational diabetes
- Physical activity and pregnancy
Guidance from the Physical Activity and Pregnancy Study, commissioned by the UK Chief Medical Officers
- Shoulder dystocia
- Understanding how risk is discussed in healthcare
- NHS Eat well:
- Tommy’s information on weight management during pregnancy:
- NHS BMI calculator:
- Weight gain in pregnancy:
A full list of useful organisations (including the above) is available at Other sources of help.
If you are asked to make a choice, you may have lots of questions that you want to ask. You may also want to talk over your options with your family or friends. It can help to write a list of the questions you want answered and take it to your appointment.
Ask 3 Questions
To begin with, try to make sure you get the answers to 3 key questions, if you are asked to make a choice about your healthcare:
- What are my options?
- What are the pros and cons of each option for me?
- How do I get support to help me make a decision that is right for me?
*Ask 3 Questions is based on Shepherd et al. Three questions that patients can ask to improve the quality of information physicians give about treatment options: A cross-over trial. Patient Education and Counselling, 2011;84:379-85
Sources and acknowledgements
This information has been developed by the RCOG Patient Information Committee. It is based on the RCOG Green-top Guideline No. 72, Care of Women with Obesity in Pregnancy (published in November 2018), and the NICE guideline Weight Management Before, During and After Pregnancy (published in July 2010).
The guidelines contain a full list of the sources of evidence we have used.
This information has been reviewed before publication by women attending clinics in Manchester, Newcastle, London and Wrexham, by the RCOG Women’s Network and by the RCOG Women’s Voices Involvement Panel.