Being very overweight, or obese, which is usually defined as having a body mass index (BMI) of 30 or over, is increasingly common. Around 15-20% of pregnant women are now in this category. Your BMI is a measurement of how overweight you are and is calculated using your weight and height.
Before you get pregnant, you can use the BMI healthy weight calculator to work out if you are overweight. However, once you're pregnant, this may not be accurate.
If you are overweight, the best way to protect your health and your baby's wellbeing is to lose weight before you become pregnant. By reaching a healthy weight, you increase your chances of conceiving naturally and reduce your risk of the problems associated with being overweight in pregnancy.
Contact your GP for advice on how to lose weight. Your doctor may be able to refer you to a specialist weight loss clinic. Find out about losing weight before you become pregnant.
If you get pregnant before losing weight, try not to worry – most women who are overweight have a straightforward pregnancy and birth, and have healthy babies. However, being overweight does increase the risk of complications for both you and your baby. Good antenatal care can help to minimise these risks.
If you are very overweight and pregnant, don't try to lose weight during your pregnancy, as this may not be safe. There is no evidence that losing weight while you're pregnant will reduce the risks.
The best way to protect your health and your baby's health is to go to all your antenatal appointments so that the midwife, doctor and any other health professionals can keep an eye on you both. They can manage the risks that you might face due to your weight, and act to prevent – or deal with – any problems.
It's also important to eat a healthy, balanced diet and get some physical activity every day. You should be offered a referral to a dietitian or other health professional for personalised advice on healthy eating and how to be physically active during your pregnancy. Being physically active in pregnancy will not harm your baby.
Read about how to have a healthy diet while pregnant.
Eating and exercise
Eating healthily (including knowing what foods to avoid) and doing activities such as walking and swimming is good for all pregnant women. If you weren't active before pregnancy, it's a good idea to consult your midwife or doctor before starting a new exercise regime when you're pregnant.
If you start an aerobic exercise programme (such as swimming, walking, running or aerobics classes), tell the instructor that you're pregnant and begin with no more than 15 minutes of continuous exercise, three times a week. Increase this gradually to daily 30-minute sessions.
Remember that exercise doesn't have to be strenuous to be beneficial. As a general rule, you should be able to hold a conversation as you exercise when pregnant. If you become breathless as you talk, you're probably exercising too strenuously.
Find out more about exercising while pregnant.
Your care in pregnancy
If you become pregnant before losing weight, you'll be tested for gestational diabetes. You may also be referred to an anaesthetist to discuss issues such as having an epidural during labour. You're more likely to need this type of pain relief, because very overweight women are more likely to have an instrumental delivery (ventouse or forceps or caesarean), and it can be difficult for the epidural to be given.
If you're overweight, discuss your birth options with your midwife or doctor, because there are restrictions on which women can safely deliver at home or in a birthing pool. Because overweight women are more likely to need forceps, ventouse or caesarean to give birth, it's usually safer to opt for a hospital birth, where there's faster access to medical care and pain relief options, if needed.
Find out more about your options on where to give birth.
The National Institute for Health and Care Excellence (NICE) has produced guidelines on weight management before, during and after pregnancy. It is not aimed at women who have a BMI over 30, but it has useful information on achieving, and maintaining, a healthy weight.
Risks of being overweight in pregnancy
Being overweight increases the risk of complications for pregnant women and their babies. The higher a woman's BMI, the higher the risks. The increasing risks are in relation to:
- miscarriage – the overall risk of miscarriage under 12 weeks is one in five (20%); if you have a BMI over 30, the risk is one in four (25%)
- gestational diabetes – if your BMI is 30 or above, you are three times more likely to develop gestational diabetes than women whose BMI is below 30
- high blood pressure and pre-eclampsia – if you have a BMI of 35 or above at the beginning of your pregnancy, your risk of pre-eclampsia is twice that of women who have a BMI under 25
- blood clots – all pregnant women have a higher risk of blood clots compared to women who are not pregnant, and if your BMI is 30 or more the risk is additionally increased
- the baby's shoulder becoming "stuck" during labour (sometimes called shoulder dystocia)
- heavier bleeding than normal after the birth
- having a baby weighing more than 4kg (8lb 14oz) – the overall risk of this for women with a BMI between 20 and 30 is 7 in 100 (7%); if your BMI is over 30, your risk is doubled to 14 in 100 (14%)
You are also more likely to need an induction and instrumental (ventouse or forceps) delivery, and an emergency caesarean section.
Problems for your baby can include being born early (before 37 weeks), and an increased risk of stillbirth (from an overall risk of 1 in 200 in the UK to 1 in 100 if you have a BMI of 30 or more). There is also a higher risk of foetal abnormality, such as neural tube defects like spina bifida. Overall, around 1 in 1,000 babies are born with neural tube defects in the UK. If your BMI is over 40, the risk is three times the risk of a woman with a BMI below 30.
These problems can also happen to any pregnant woman, whether she is overweight or not.
Bear in mind that although these risks are increased if your BMI is 30 or over, most women who are overweight will have a healthy baby.
You can find out more in a leaflet from the Royal College of Obstetricians and Gynaecologists, called Why your weight matters during pregnancy and after birth.