Advice after your nerve block for surgery
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BMI is a way to check if your weight is healthy for your height.
BMI Ranges
- Less than 18.5 = underweight
- 18.5 – 24.9 = healthy weight
- 25 – 29.9 = overweight
- 30 – 34.9 = obese
- 35 or more = morbidly obese
Your BMI is checked at your first booking visit. This helps make sure you get the right care during pregnancy.
Aim to keep your BMI between 20 and 25.
If your BMI is over 24.9, losing weight can:
- lower risks during pregnancy.
- improve chances of fertility treatment working (if needed).
If your BMI is over 30:
- take 5mg folic acid (prescribed by your GP) starting at least 1 month before pregnancy and during the first 3 months.
- take 1000 IU Vitamin D every day during pregnancy and while breastfeeding.
- Your midwife will give you advice on healthy eating and staying active to manage your weight.
- Do not try to lose weight unless your midwife tells you to.
You will have:
- ultrasound scans at 11–13 weeks and 20–22 weeks. These scans may not be as clear as for women with a normal BMI.
- a glucose tolerance test (blood test) is offered at 28 weeks to check for diabetes.
- your midwife or doctor will check your risk of blood clots (thrombosis).
- You will be advised to have your baby in hospital with consultant-led care.
- You will have extra ultrasound scans to check your baby’s growth and position.
- After each scan, you will see a consultant.
- You may see a dietitian for advice.
- You may meet an anaesthetist to check risks if you need an epidural.
- The hospital will make sure the right equipment is ready for your birth.
The higher your BMI, the higher the risk of problems.
Antenatal Risks:
- Harder to scan and check baby’s growth and position.
Pregnancy Risks:
- Gestational Diabetes
- High blood pressure
- Large or small babies
- Higher risk of stillbirth
- Blood clots
Labour Risks:
- More pain relief needed
- Harder to give epidural
- Higher chance of induction or Caesarean
- Longer surgery time
- Shoulder dystocia (baby’s shoulders stuck)
- More chance of tears and instrumental delivery
Postnatal Risks:
- Infection
- Blood clots
- Heavy bleeding
- Trouble breastfeeding
- Longer hospital stay
- Pethidine (a pain medicine) may not work as well as for women with a normal BMI.
- If you choose an epidural, it may be harder for the doctor to put it in and make sure it works properly.
- It may be harder to check your baby’s heartbeat. Your midwife might suggest using a fetal scalp clip on the baby’s head to monitor the heart rate.
- Your midwife will encourage you to move around during labour. If you stay still, you can get sore skin or pressure marks. If you can’t walk, change positions often.
- If you stay still for too long, you have a higher risk of blood clots. If you need a Caesarean section, you will wear special stockings and have injections to thin your blood.
If Your BMI is Over 40
- You cannot use the birthing pool.
- Your midwife, health visitor, or GP can give advice on healthy eating, exercise, and contraception.
- Breastfeeding for 12 months or more can help with weight loss.
- If you are very overweight, your care will be planned based on your mobility and the space available in the bed.
- Try to lose weight before your next pregnancy. This will lower your risks and help your long-term health.
Contact us
If you have any queries relating to this information, please contact the Maternity service.
About this information
Service:
Maternity
Reference:
M/035
Approval date:
1 March 2026
Review date:
1 March 2029
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Important note
This page provides general information only. It is developed by clinical staff and is reviewed regularly every 3 years for accuracy. For personal advice about your health, or if you have any concerns, please speak to your doctor.