Am I having a big baby?

How will I know if I’m having a big baby?

It’s hard to tell if your baby is big until they are weighed when they are born. Many women worry that they are having a big baby if they have a big bump. Equally, some women worry that their bump is too small and their baby isn’t growing well.

In the same way that every woman’s body is different, every baby bump is different. The size of your pregnancy bump does not necessarily mean your baby is too large or too small or that your baby is not healthy and well. Baby bumps come in all different shapes and sizes. 
Remember that your midwife is there to listen to any concerns you have about pregnancy.

There are no silly questions. So, if you have any concerns about how your baby is growing, tell your midwife how you feel. 

Your midwife may suspect your baby is big when they start measuring your baby bump. An ultrasound may also show a big baby. 

Doctors and midwives define big babies in two ways. You may hear them talking about either of the following.

Large for gestational age

Your baby’s weight and height will be measured from about 2 weeks after they are born and monthly until they are about 6 months. Their growth will be recorded on a chart in their personal child health record (known as the red book) which you are given after your baby is born. 

The lines on these charts are called centile lines. Weights and heights that are anywhere within the centile lines are considered normal. 

Babies that are ‘large for gestational age’ means babies that are born over the 90th percentile. This means that the baby weighs more than 90% of babies born at the same gestational age in the population. 

Macrosomic

Macrosomia is a term that describes a baby that is born with a birthweight above 4000g (4kg). This applies to babies born at any gestational age.

Giving birth to a big baby can be a common worry for pregnant women. But most big babies are born healthy and your birth plan (how you want to give birth) may not necessarily be affected.

How will my baby bump be measured?

Your midwife will ask you to lie down and will measure from the top of your bump to the top of your pubic bone using a tape measure. These measurements should be taken at each antenatal visit from around 24 weeks. 

Why am I having a big baby?

There are many reasons why you may be more likely to have a bigger baby. This includes if you:

• have a body mass index of over 30 during pregnancy
• go more than 2 weeks past your due date (you will likely be offered an induction to avoid this)
• have type 1 or 2 diabetes or develop gestational diabetes
• were a bigger baby yourself
• are an older mum (more than 35 years old). 

There is limited research about how much the father’s size at birth influences the size of your baby. 

If any of these apply to you, try not to worry. This does not mean you will definitely have a big baby. 

Can I reduce the risk of having a big baby?

The best thing you can do is eat healthily and stay active during pregnancy. This will help you manage your weight gain and reduce the risk of developing gestational diabetes.

If you have type 1 or 2 diabetes in pregnancy, you will get extra care to make sure your condition is well managed throughout your pregnancy. This can help reduce the risk of your baby growing larger and faster than usual (known as macrosomia). Find out more about managing type 1 or type 2 diabetes during pregnancy. 

Will having a big baby affect my birth?

If your doctor or midwife think that you’re having a big baby, this does not necessarily mean you cannot give birth vaginally, if this is what you want. 

Your doctor or midwife may not be certain that your baby is large for their gestational age until they are born, so this will need to be taken into account when you decide how to give birth.

Your doctor or midwife will talk to you about the advantages and disadvantages of giving birth vaginally and by caesarean section. These may include:

• a higher chance of medical problems for you such as infection if you need an emergency caesarean section
• a higher chance of shoulder dystocia with vaginal birth
• a higher chance of instrumental birth and perineal tear with vaginal birth. 

It’s important to remember that either way of giving birth carries some risk, whether you are having a big baby or not. The important thing is that you make an informed decision about your care that you are most comfortable with. Talk to your doctor or midwife about your options for where and how you would like to give birth. It is a good idea to write a birth plan.

If you have type 1, type 2 or gestational diabetes and suspected macrosomia 

If you have type 1 or type 2 diabetes or have developed gestational diabetes, you will usually be offered an early induction of labour or planned caesarean section. This will reduce the risk of shoulder dystocia. 

However, how you deliver your baby is ultimately your choice and some women with diabetes have a natural vaginal birth. Talk to your healthcare team for more information about giving birth with type 1 or 2 diabetes or with gestational diabetes.

Will my baby’s health be affected?

Most big babies are born healthy. Since many large babies are born to mothers with diabetes, some babies will need help regulating their blood sugar after they're born. They may also need help with their breathing. 

Jaundice is common in newborn babies and especially in babies of mothers with diabetes. This is a usually harmless condition in newborn babies that causes yellowing of the skin and the whites of the eyes. Jaundice is caused by the build-up of bilirubin in the blood. Your baby may need to be monitored in the neonatal unit. 

Visit NHS Choices to find out more about newborn jaundice.

Find out more about your baby’s health if you have type 1 or type 2 diabetes.

Regardless of their size at birth, a baby's weight is always monitored closely after they are born to make sure they are healthy and growing properly. But their weight isn't the only thing that's important. How your baby is feeding and the number of wet nappies and poos they do every day can also indicate that your baby is doing well. Find out more about after your baby is born.

Talk to your doctor or midwife if you have any questions about your baby’s growth during pregnancy. You can also call speak to our midwives on our pregnancy line on 0800 014 7800 (Monday to Friday, 9am to 5pm), or email us at [email protected].