Information for pregnant women with a body mass index (BMI) of 30 or more

Key messages

• Most women and birthing people with a raised BMI have a straightforward pregnancy and birth.
• Enjoy a normal healthy diet and keep your weight gain to a minimum.
• Keep active and take regular, moderate intensity exercise.
• Take a high-dose folic acid supplement of 5mg daily for the first 12 weeks of pregnancy to reduce the risk of neural tube defects.
• Take 10micrograms (400IU) of vitamin D throughout pregnancy and during breastfeeding.
• Women and birthing people with a raised BMI are at a higher risk of complications during pregnancy and labour, therefore discussions with your midwives and doctors regarding appropriate place of birth and antenatal care are essential.
• Following birth, mobilise as soon as possible, especially if you have a caesarean.
• Breastfeeding your baby can aid weight loss and is recommended to reduce the risk of obesity for your baby in later life.
• Reducing your BMI by 5kg/m² will reduce your chances of gestational diabetes in your next pregnancy by 80%.

What is body mass index (BMI)?

Body mass index (BMI) is calculated by your weight to height ratio and is a practical estimation, used by health professionals, of weight range. It is measured in kg/m².

At your booking visit with your midwife, we will offer to calculate your BMI by measuring your height and weight.

Research shows that there is an association between a raised BMI of 30 or more at the start of pregnancy and an increase in complications during pregnancy and labour, with a BMI of 40 or more having further chance of complications. Additional care recommendations are therefore made by the Royal College of Obstetricians and Gynaecologists (RCOG) and the National Institute for Health and Care Excellence (NICE). This information leaflet outlines these recommendations.

Pregnancy and birth complications associated with a raised BMI

Diabetes

The higher the BMI the greater the risk of developing diabetes in pregnancy. You will therefore be offered an oral glucose tolerance test (OGTT) to check for diabetes at 24 weeks of pregnancy.

Raised blood pressure

If you have a BMI of 35 or more, you have an increased risk of developing a serious pregnancy-related disease called pre-eclampsia. Your risk will be assessed by your community midwife. You will be offered regular blood pressure checks, and we may recommend medication to help reduce this risk.

Blood clots

Women and birthing people with a higher BMI have an increased risk of blood clots. Therefore, you will be assessed in early pregnancy and after birth, and you may be offered anticoagulant therapy (blood thinning injections) and support stockings to reduce the risks.

Less accurate ultrasound scans

Everybody is offered a scan in their pregnancy to check the baby’s major organs, size and physical characteristics. If there is a lot of excess body fat around your tummy, ultrasound scan pictures can be unclear. This can limit our ability to identify any problems, completely exclude abnormalities or see how well the baby is growing.

It may also be more difficult to feel your baby’s position and size during routine antenatal checks, so a scan may be required or offered at around 36 weeks to check whether your baby is head down before you go into labour.

Recommendations for care in pregnancy

BMI of 30 or more

• A glucose tolerance (OGGT) blood test at 24 weeks to check for diabetes.
• Re-measurement of your weight at 34 to 36 weeks to allow for appropriate assessment of needs and drug doses.

BMI of 35 or more

• Take a high dose folic acid supplement of 5mg (milligrams) daily for the first 12 weeks of pregnancy to reduce the risk of neural tube defects. This will need to be prescribed by your GP.
• Take 10 micrograms of vitamin D throughout pregnancy and during breastfeeding (this is advised to all pregnant women and birthing people).
• A referral to see a consultant obstetrician to discuss your antenatal care and your plans for birth.
• You may be offered, or you can request a referral to a dietitian.
• If you have additional risk factors for pre-eclampsia you may also be advised to take 150mg aspirin daily. This will be assessed by your midwife at your booking appointment.
• If you have a raised BMI it may be difficult to accurately feel the size or position of your baby, therefore you will be offered an additional scan at 32 and 36 weeks of pregnancy to check the growth and position of your baby.
• An up-to-date height, weight and BMI calculation will be offered in the third trimester of pregnancy.
• If your BMI is 40 or more at your booking appointment, you will also be offered an antenatal appointment to see an obstetric anaesthetist to undertake an assessment and discuss specific risks in relation to any analgesia and/or operative procedures which may be required.

Risks during labour and giving birth associated with a raised BMI

It is worth remembering that most women with a BMI of 30 or more have straightforward births. However, we know that women who have a high BMI have more chance of having:

• Monitoring difficulties: your baby’s heart rate can be more difficult to monitor (especially in labour). Therefore, it may be recommended that a clip is put on your baby’s head (attached by passing a small lead through the vagina and cervix) to accurately monitor your baby’s heart rate if continuous monitoring is required. This might mean that we would need to break your waters first.
• Restricted mobilisation: this may be restricted during your labour due to monitoring difficulties. This can lead to an increased risk of needing an assisted birth. If your BMI is over 40 you will also be assessed during pregnancy for the best way to help you move from bed to chair etc and to assess any extra risks to your skin of pressure sores.
• Difficulty carrying out procedures: taking blood or putting a drip in can be more difficult, so this will tend to be offered early in labour, particularly if your BMI is 40 or more.
• Difficulties with epidural/spinal analgesia: it can be more difficult and take longer to give epidurals and spinals if you have a higher BMI, and effective epidural analgesia may not be possible.
• Assisted delivery: increased chance of needing a ventouse (suction cup), forceps or caesarean birth.
• Bigger babies: may lead to difficulties delivering your baby’s shoulders. This is called a 'shoulder dystocia', and is an emergency situation.
• Increased risk of bleeding: the risk of bleeding is increased following birth, particularly if your baby is large. To reduce this risk, we will recommend ‘active management’ for the delivery of the placenta which is when we offer an injection of oxytocin as your baby is born.

Because of these increased risks, there are recommendations on place of birth:

Delivery Unit

This is the recommended place of birth for women and birthing people with a BMI of 35 or more who are having their first baby, and for all women and birthing people with a BMI of 40 or more.

Rosie Birth Centre

If this is your second or subsequent birth and your BMI is between 35 and 39.9, you may be suitable to use the Rosie Birth Centre following an antenatal discussion and individualised plan of care made with your community midwife. If this is your first birth, the Rosie Birth Centre would not be recommended.

Home birth

This is not recommended for women with a BMI of 35 or more, therefore if you choose to birth at home, you should have an individualised plan of care made with your community midwife, consultant obstetrician and/or consultant midwife.

Further information

You may find the following websites helpful:

• The National Institute for Health and Care Excellence (NICE) (opens in a new tab)
• Healthy Choices (opens in a new tab)
• Healthy Start (opens in a new tab)

References

Centre for Maternal and Child Enquiries (CMACE) and Royal College of Obstetricians and Gynaecologists (RCOG) Joint Guideline ‘Management of Women with Obesity in Pregnancy’, 2010.