Why does my weight in pregnancy make a difference?
Most women and birthing people who are overweight have a straightforward pregnancy and birth and have healthy babies. But being overweight or obese can increase the risk of complications to both you and your baby.
Your midwife will want to be aware of this so they can offer you the right care and you can work together to reduce some of those risks.
At your first antenatal visit (the booking appointment) your midwife will measure your body mass index (BMI). This is a measure that uses your height and weight to work out if your weight is healthy and will be based on your weight before pregnancy.
If you have a high BMI you will get extra advice and care during your pregnancy.
BMI is not a perfect way to measure your weight because it cannot tell the difference between excess fat, muscle or bone. But it is still the best way of assessing your weight medically.
BMI weight ranges
The BMI weight healthy range is different for different ethnicities.
People with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background have a higher risk of developing some long-term conditions, such as type 2 diabetes, with a lower BMI.
If you are in these groups a BMI:
- below 18.5 is underweight
- between 18.5 and 23 is healthy
- over 23 means increased risk (overweight)
- over 27.5 means high risk (obese).
For people of White heritage, a BMI:
- below 18.5 is underweight
- between 18.5 and 24.9 is healthy
- between 25 and 29.9 is overweight
- of 30 or over is obese.
Why does the BMI calculation change for different ethnic groups?
The BMI definition of obesity (a BMI of 30+) was originally developed using data mostly from White populations. Since then, research has found that people from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, have a higher risk of developing some long-term conditions, such as type 2 diabetes, when they have a lower BMI.
As a result, the NHS has developed guidelines to make sure that people from these ethnic backgrounds get help to prevent developing type 2 diabetes earlier than people from White backgrounds.
There is not enough evidence yet to say whether people from different ethnic backgrounds should have different pregnancy care based on their weight.
This means that how your BMI is calculated, as well as the advice and care you will have about your weight in pregnancy is the same for all women and birthing people, whatever your ethnic background.
What are the risks of a high BMI when I’m pregnant?
If you have a high BMI (over 25) before pregnancy or in early pregnancy, this can affect your health and how your baby develops. The higher your BMI the higher the risks.
This can be tough to read but try not to worry. Your healthcare team will monitor your pregnancy carefully as it progresses. Remember that most women and birthing people who are overweight have a straightforward pregnancy and birth and have healthy babies.
These risks include the following.
If you have a BMI of 30 or above, the risk of an early miscarriage slightly increases.
The overall likelihood of a miscarriage in early pregnancy is 1 in 5 (20%). If you have a BMI of 30 or above, your risk increases to 1 in 4 (25%).
High blood pressure and pre-eclampsia
If you have a BMI of 30 or above, your risk of pre-eclampsia is 2–4 times higher compared with those with a BMI under 25.
Your blood pressure and urine will be monitored at every antenatal care appointment. Your healthcare professional may recommend a low dose of aspirin to reduce the risk of you developing pre-eclampsia.
The overall likelihood of stillbirth in the UK is 1 in every 200 births. If you have a BMI of 30 or above, the risk of stillbirth is 1 in every 100 births.
Thrombosis (blood clots)
Pregnancy increases the risk of developing blood clots. If you are overweight, the risk increases.
Anyone can develop diabetes during pregnancy. But if your BMI is 30 or above, you are 3 times more likely to develop gestational diabetes compared with women with a BMI under 25.
You will be offered tests for gestational diabetes during your pregnancy.
Baby with a high birth weight
If you are overweight, you are more likely to have a baby weighing more than 4 kg, which increases the risk of complications for you and your baby during birth.
Higher risk of neural tube defects
If you are overweight before pregnancy or in early pregnancy, this can affect the way your baby develops in the uterus (womb). Overall, around 1 in 1000 babies in the UK are born with neural tube defects (problems with the development of the baby’s skull and spine). A higher dose of folic acid helps to reduce the risks of your baby having a neural tube defect (see below).
These risks may be difficult to read. But there are things you can do to have a healthier pregnancy. You will also get extra professional care during your pregnancy.
“As an overweight person you can be made to feel like the worst mum in the world because you are overweight. But all that any woman wants is a healthy pregnancy and baby.
Try not take it to heart or feel targeted when healthcare professionals talk about obesity, because they are just following what the guidelines say. Remember that managing your weight and making healthier food choices is useful advice for everyone in pregnancy, regardless of their size. You are making informed choices that are the best for you and your baby, just like everyone else.”
Tammy, mother of 6
If I’m pregnant and my BMI is above 30, is it too late to reduce these risks?
There are plenty of things you can do to make sure you have a healthier pregnancy. While it’s unlikely you can reduce all the risks, the following will make a difference:
- go to all your antenatal appointments and scans, and make sure you have any recommended blood pressure or gestational diabetes tests
- eat well and stay active
- take all the recommended supplements (see below)
- follow any specialist advice from a dietitian or anyone else involved in your care.
Should I try and lose weight while I’m pregnant?
Even if your BMI is above 30, dieting while you’re pregnant is not advised as you might cut out nutrients that your baby needs. Focus on eating healthily.
If you eat well you may not gain any weight during pregnancy and you may even lose a little bit. This is not harmful.
What extra healthcare and tests will I get during my pregnancy?
If you have a BMI of 30 or more, you should be referred to a dietitian who will help you with healthy eating and exercise.
You will also have:
- extra ultrasound scans to check the baby’s development
- a gestational diabetes test between 24-28 weeks
- a risk assessment for thrombosis (blood clots in your legs or lungs) at your first antenatal appointment. This will continue to be monitored throughout your pregnancy.
Depending on the results of your risk assessment, you may also need to have injections of low molecular weight heparin, to reduce your risk of blood clots.
Pregnancy supplements if you’re overweight
Folic acid helps to reduce the risks of your baby having a neural tube defect. If your BMI is 30 or above, you should take a daily 5mg dose of folic acid. This is a higher dose than the usual pregnancy dose, so you’ll need a prescription from your doctor. Ideally, this should be taken a month before you get pregnant and until you reach your 13th week of pregnancy. If you didn’t take it before you got pregnant, do not worry, just start taking it now until you are 13 weeks.
This is a higher dose than the usual pregnancy dose, so you’ll need a prescription from your doctor. Prescriptions are free in Scotland, Wales and Northern Ireland. You will get free prescriptions (medicine) and NHS dental care during pregnancy and for a year afterwards if you live in England.
Your midwife, GP, practice nurse or health visitor will need to apply for your maternity exemption certificate (MatEx). They can either apply online or ask you to fill in form FW8.
Vitamin D supplements
All pregnant women are advised to take a daily dose of 10 micrograms of vitamin D supplement. If your BMI is over 30 it’s more likely that you are lacking vitamin D. So, it’s extra important to remember your vitamin D supplements.
Help to buy healthy foods and vitamins
You don’t need to buy the more expensive branded vitamins, pharmacy or supermarket own brand vitamin D is just as effective.
- avoid eating for 2
- base your meals on wholegrain starchy foods such as potatoes, brown bread, brown pasta or rice
- 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 5 portions of a variety of fruit and vegetables each day, instead of foods higher in fat and calories
- eat a low-fat diet
- eat as little as possible of the following: fried food, drinks and sweets/biscuits high in added sugars, and other foods high in fat and sugar
- always have breakfast
- watch the portion size of your meals and snacks and how often you eat.
Read more about healthy eating during pregnancy.
If you’re new to exercise start gradually with no more than 15 minutes of continuous exercise, 3 times a week. From here, aim to build up to around 30 minutes 5 times a week. If you’re already active, keep it up during your pregnancy.
Find out about exercise in pregnancy.
You can also try making your everyday life more active by:
- making activities such as walking, cycling, swimming, low-impact aerobics and gardening part of your daily life
- taking the stairs instead of the lift or go for a walk at lunchtime
- avoiding sitting for long periods, watching television or at a computer, for example.
Being overweight and giving birth
Most people who are overweight have a safe and uncomplicated labour and birth. However, there is a higher risk of complications during labour or birth (particularly if your BMI is over 40). These include:
- a longer labour
- premature birth (baby born before 37 weeks)
- needing an emergency c-section
- shoulder dystocia (when the baby’s head has been born but one of the shoulders becomes stuck behind the mother’s pubic bone during a vaginal birth)
- more complications during and after a caesarean section, such as heavy bleeding and wound infection
- heavy bleeding after birth (postpartum haemorrhage) after a vaginal birth.
Because of these risks you may be advised to give birth in a hospital because you will have quicker access to medical support.
Your doctor (obstetrician) or midwife will talk to you about the best and safest birth plan for you during your pregnancy. Ultimately, where and how you give birth is your decision.
To reduce your risk of postpartum haemorrhage, your healthcare professional will recommend having an injection to help with the delivery of the placenta (afterbirth).
You may be offered an appointment with an anaesthetist (a doctor who specialises in pain relief) to talk about the best pain relief during labour.
You may decide to have a planned c-section if your healthcare team think it is the safest option for you and your baby. Find out more about c-section advice for overweight women and birthing people.
Looking after your emotional health
Pregnancy can be a very emotional time for everyone. Being overweight slightly increases your risk of developing mental health problems in pregnancy and after birth.
If you are struggling, don’t hide your feelings or suffer in silence. You are not alone. Tell you partner, family or friends how you feel, as well as your GP and midwife. They will help you get the support you need.
Find out more about your mental health before, during and after pregnancy.