Obesity, which is usually defined as having a body mass index (BMI) of more than 30, is increasingly common. Around 15-20% of pregnant women are now obese. Your BMI is a measurement of obesity calculated using your weight and height.
Before you get pregnant you can use the BMI healthy weight calculator to work out your BMI. But once you're pregnant this may not be accurate.
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 obesity 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 more about losing weight before you become pregnant.
If you get pregnant before losing weight, try not to worry – good antenatal care can help minimise any risks to you and your baby.
During pregnancy
If you are obese and you are pregnant, you should not try to lose weight during your pregnancy as this may not be safe. Although there are risks associated with being obese during pregnancy, there is no evidence that losing weight while you're pregnant will reduce these 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 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.
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, always 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 exercise in pregnancy.
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 obese 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 obese, 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 obese 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 (PDF, 68kb). 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 obesity
Obesity can cause problems both with becoming pregnant and during pregnancy. You may have difficulty conceiving and if you're having fertility treatment it may not be as effective. In pregnancy, a BMI over 30 increases the risk of a range of health problems for you and your baby:
You are also more likely to need:
Most women who are obese in pregnancy have a successful pregnancy, but problems for your baby can include:
- stillbirth
- birth defects (congenital abnormality)
- a higher chance of health problems later in life, including obesity and diabetes
