What is Body Mass Index (BMI)
Your ideal weight range is measured by the Body Mass Index (BMI), which is calculated by dividing your weight in kilograms by your height in metres and ideally women in early pregnancy should have a BMI of 20–25. The BMI is usually calculated at your first booking appointment as it forms part of your patient records for pregnancy. Women with a BMI of more than 30 at the start of pregnancy are overweight to a degree that can cause problems during pregnancy and birth when extra strain is placed on joints, muscles and many other organs, including the heart and lungs. This leaflet gives you information about the possible problems and the specialised care that you will be offered during your pregnancy and labour.
What problems could arise during my pregnancy?
Over the past few decades, there is a lot of evidence that shows that a mother’s BMI in the first trimester of pregnancy is associated with an increased risk of many complications in pregnancy. In general, the higher the mother’s BMI, the greater the risk of complications. It is worth noting that most women with a BMI greater than 30 will have a healthy baby.Some of these complications are listed below:
Complications for the mother:
- Increased blood pressure (essential hypertension) or Pre-eclampsia
- Tiredness and shortness of breath
- Miscarriage – the overall risk of miscarriage under 12 weeks is 1 in 5 (20%), but if you have a BMI over 30, your risk increases to 1 in 4 (25%).
- Preterm labour
- Diabetes during pregnancy (gestational diabetes)
- Lack of vitamin D
- Venous thromboembolism (blood clots in the legs and lungs)
- Difficulty monitoring the baby during childbirth. If it is difficult for the midwife to monitor your baby’s heart or contractions it may be necessary to use an electronic monitor with a small clip attached to the skin on your baby’s head
- Difficulty in both normal delivery and caesarean section.
- Bleeding after childbirth
- Complications with general anaesthesia
- It may be difficult to obtain a good quality ultrasound scan to monitor your baby’s growth and development.
- Back and joint pain.
Complications for the baby:
- Congenital abnormalities – your baby can be at risk of having problems with the development of the brain and spine such as spina bifida.
- Stillbirth and neonatal death.
- Macrosomia – a newborn much larger than average. Your baby is more likely to weigh more than 4 kg. If your BMI is above 30, your risk doubles from 7% to 14% compared to women with a BMI between 20 and 30.
- Shoulder dystocia (difficulty with the birth of the baby’s shoulders).
- Admission to the neonatal unit.
- If you are overweight, your baby will have an increased risk of obesity and diabetes later in life.
What can I do to avoid or reduce these problems?
Healthy diet
Monitor your diet to avoid gaining too much weight; eat a healthy diet with plenty of fruit and vegetables avoiding sugary foods and foods that contain a lot of fat. If you have a high BMI a weight gain of no more than 6kg during pregnancy is recommended. A gain of much more than this will tend to stay with you afterwards.
- Base your meals on starchy foods such as potatoes, bread, rice and pasta, choosing wholegrain where possible.
- Watch the portion size of your meals and snacks and how often you eat. Do not ‘eat for two’.
- Eat a low-fat diet. Avoid increasing your fat and/or calorie intake. Eat as little as possible of the following: fried food, drinks and confectionary high in added sugars, and other foods high in fat and sugar.
- Eat fibre-rich foods such as oats, beans, lentils, grains, seeds, fruit and vegetables as well as wholegrain bread, brown rice and pasta.
- Eat at least five portions of a variety of fruit and vegetables each day, in place of foods higher in fat and calories.
- Always eat breakfast. In general, you do not need extra calories for the first two-thirds of pregnancy and it is only in the last 12 weeks that women need an extra 200 kilocalories a day
Trying to lose weight by dieting during pregnancy is not recommended, however, by making healthy changes to your diet you may not gain any weight during pregnancy and you may even lose a small amount which is is not harmful.
Physical activity
Keep as active as you can; avoid spending long periods sitting or lying, use stairs instead of lifts, walk instead of using the car for every journey. Moderate-intensity physical exercise such as swimming or brisk walking for 15–30 minutes daily is beneficial for you and your baby. If you are new to exercise, then start gradually with 15 minutes and build your stamina up. However, if you already participate in regular exercise then continue. In later pregnancy you may find that “non-weight bearing” activities such as swimming are easier to keep up. If you experience joint or back pain you can see the Women’s Health physiotherapy team to receive advice about posture, sleeping positions, lifting and carrying.
Vitamin D
Take a daily supplement of vitamin D throughout pregnancy.
Folic acid
It is also helpful to take a daily supplement of folic acid for the first 3 months of pregnancy. Ideally the folic acid should be started when you are trying for a baby. You will be offered a glucose tolerance test to detect gestational diabetes.
Anaesthetic review
If your BMI is above 40 you may be offered a review by an anaesthetist before the birth of your baby in order to discuss your thoughts on pain relief for your labour and delivery of your baby. It may also be to discuss anaesthetic choices should you require an anaesthetic at the time of the birth of your baby. It is easier to do this in relaxed surroundings, rather than trying to give explanation when you are coping with labour. You have all the same choices for pain relief in labour as any other mother but some options such as epidurals or having intravenous drips can take longer if you have a high BMI.
It could be more difficult and take longer to get an epidural in and working if you suddenly decide you would like one, so the anaesthetist may offer advice on planning for an epidural earlier in labour. They will examine your back at this visit and will do routine checks so that they are prepared should you require an anaesthetic at the time of the birth of your baby. If you need a caesarean section, you will be advised to have a spinal or epidural anaesthetic as this will be safer for you than a general anaesthetic.
How might a raised BMI affect my labour?
Pain management options such as TENs, aromatherapy, relaxation, gas and air (entonox) are unaffected by BMI, but a larger dose of Pethidine or Diamorphine might be needed to give you adequate pain relief. Epidurals can be more difficult to place and unfortunately are less likely to be completely effective.
You are more likely to have a bigger than average baby and hence may need a Caesarean section or other assistance with your baby’s birth such as forceps or ventouse (suction) delivery.
If you have had a caesarean section for a previous birth and have a BMI above 35, the chance of a normal delivery in your next pregnancy is reduced. The option of a planned (elective) caesarean section will be discussed with you. Heavy bleeding (haemorrhage) during or shortly after the birth, is more common if your BMI is raised.
After your baby’s birth
You should try to get up and about again as soon as possible to reduce your risk of blood clotting problems, wound and chest infections.
- You will be advised to wear support stockings which reduce the chances of a thrombosis (blood clot) and you will be prescribed anti-clotting injections, if you are thought to be at a higher chance of clotting problems.
- Monitor your diet making sure you eat a balanced diet but do not over eat. One of the best things you can do for your baby is to promote a healthy lifestyle thus preventing the problem of becoming overweight later in life.
- Breast feeding is the ideal start to this, with the added advantage that most women find that they naturally lose weight whilst they are breast feeding. Skin to skin contact with your baby is important to promote breastfeeding. Whilst you are breastfeeding do not start on any strict weight-reducing diets. You should continue to take vitamin D supplements while you are breast feeding.
Your future health
Unfortunately, many women find it difficult to lose the weight gained during pregnancy but do try to return to your pre-pregnancy BMI and, if possible, reduce it further particularly if you are planning future pregnancies. Not only will this mean that you are fitter and so better able to cope with the demands of a young family, but it will help to reduce the likelihood of problems in future pregnancies. A woman with a raised BMI is more likely to have difficulty conceiving and is at greater risk of miscarriage.
Dr Efterpi Tingi
Consultant Obstetrician and Gynaecologist
