Pregnancy information

Overweight and pregnancy

Being overweight when you're pregnant increases the chance of some complications such as gestational diabetes. Make sure you go to all your antenatal appointments so your pregnancy team can monitor the health of you and your baby.

Your weight before you get pregnant

Before you get pregnant, you can use the BMI (body mass index) healthy weight calculator to work out if you are overweight. Your BMI is a measurement based on your weight to height. However, once you're pregnant, this measurement may not be accurate.

A BMI of 25 to 29.9 means you're overweight, A BMI of 30 or above means you're very overweight, or obese.

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 the chance of problems associated with being overweight in pregnancy.

See a GP for advice on how to lose weight. Your doctor may be able to refer you to a specialist weight-loss clinic.

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 chance of complications for both you and your baby.

Your weight during pregnancy 

If you are very overweight (usually defined as having a BMI of 30 or above) and pregnant, do not 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 chance of complications.

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 problems that you might face due to your weight and take steps to prevent or deal with them.

It's also important to eat a healthy, balanced diet and do 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.

Eating and Exercise

Eating healthily (including knowing what foods to avoid in pregnancy) and doing activities such as walking or swimming is good for all pregnant women.

If you were not active before pregnancy, it's a good idea to consult your midwife or doctor before starting a new exercise plan when you're pregnant.

If you start an aerobic exercise programme (such as swimming, running or aerobics classes), tell the instructor that you're pregnant. Begin with no more than 15 minutes of continuous exercise, 3 times a week. Increase this gradually to daily 30-minute sessions.

Remember that exercise does not 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.

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 pain relief in labour. You're more likely to need an epidural, because very overweight women are more likely to have an instrumental delivery (ventouse or forceps or a caesarean section), and it can be difficult for an epidural to be given.

If you're overweight, discuss your birth options with a midwife or doctor. Ask if there are any particular safety concerns for you around giving birth at home or in a birthing pool.

You may be advised to give birth in a hospital where there's easy access to medical care if you need it.

Find out more about your options on where to give birth.

The National Institute for Health and Clinical 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.

Possible problems if you're overweight in pregnancy

Being overweight increases the chance of complications for pregnant women and their babies. The higher a woman's BMI, the higher the chance of complications. The increasing chances are in relation to: 

  • miscarriage - the overall chance of miscarriage under 12 weeks is 1 in 5 (20%); if you have a BMI over 30, the chance is 1 in 4 (25%)
  • gestational diabetes - if your BMI is 30 or above, you are 3 times more likely to develop gestational diabetes than women who have a BMI below 25
  • high blood pressure and pre-eclampsia - if you have a BMI of 30 or above at the beginning of your pregnancy, your chance of pre-eclampsia is 2 to 4 times higher than that of women who have a BMI below 25
  • blood clots - all pregnant women have a higher chance of blood clots compared to women who are not pregnant, and if your BMI is 25 or above, the chance is increased further
  • the baby's shoulder becoming "stuck" during labour (sometimes called shoulder dystocia)
  • heavier bleeding than normal after the birth (post-partum haemorrhage)  
  • having a baby weighing more than 4kg (8lb 14oz) – the overall chance of this for women with a BMI of 20 to 30 is 7 in 100 (7%); if your BMI is above 30, your chance is doubled to 14 in 100 (14%)

You are also more likely to need an instrumental (ventouse or forceps) delivery, and an emergency caesarean section.

Possible problems for your baby if you're overweight in pregnancy

Problems for your baby can include being born early (before 37 weeks), and an increased chance of stillbirth (from an overall chance of 1 in 200 in the UK to 1 in 100 if you have a BMI of 30 or above).

There is also a higher chance of your baby having a health condition, such as a neural tube defect like spina bifida. Overall, around 1 in 1,000 babies are born with a neural tube defect in the UK. If your BMI is over 30, the chance is nearly doubled at 2 in 1,000.

These problems can also happen to any pregnant woman, whether she is overweight or not.

Bear in mind that although the chance of these problems is increased if your BMI is 30 or above, 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.

Last Updated: 16/04/2021 14:47:31
The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website