It’s a comment I hear all the time – a mum-to-be saying ‘I’ve been told I’m having a big baby’.

Everyone has a story – perhaps it is your own. Or a friend, neighbour or sister. Of a baby that is ‘too big’. One that ‘you won’t be able to birth naturally’. Or ‘let’s get baby out now before it gets any bigger’.

It seems like everyone is having an ‘above average’ baby!

This was something I heard with two of my babies – the first one born at 3kg (6 pd 10 ounces) and 2.9 kg (6 pd 6 ounces). Not big babies! My largest baby was my third at 3.4kg and not a mention of having a big baby with her.

But what does this mean and, more importantly, why does it matter if we are having a big baby?

This was my ‘suspected big baby’ – all 3.015kg  (6 pd 10 ounces) of her

What is a big baby?

Firstly, what do we mean when someone says ‘I’m having a big baby’?

The medical term for ‘big baby’ is macrosomia (literally ‘big body) is defined as bigger than 4kg or 4.5kg at birth (depending on the research you read).

How do you know if you are having a big baby?

It’s important to point out that we can’t accurately predict the weight of your baby at birth  (Chauhan et al 2005)

There are a number of ways that your caregiver can try and estimate the weight of your baby, including measuring fundal height (the size of your ‘bump’) and palpating. However these are accurate only 40 – 53% of the time.

Ultrasounds – which are commonly relied upon for assessing baby’s weight, are accurate between 15% and 79% of the time when predicting babies at 4kg – with most research showing less than 50% accuracy.

The accuracy decreases (between 22% and 37%) even further when predicting babies will be 4.5kg and over. This means that for every 10 babies predicted (using ultrasound) to be over 4.5kg, on 2 – 4 will be 4.5kg and over, with 6 – 8 weighing less.

Due to the inaccuracies, among uncomplicated pregnancies suspicion of macrosomia is not an indication for induction or for primary cesarean delivery.

So what does all that mean?

A suspected big baby is just that – suspected. And the suspicion of a big baby doesn’t make it so.

The only way to accurately measure the weight of your baby is to place them on the scales after their birth.

The impact of a suspected big baby.

The mere suspicion of a big baby can change both the way mum and her caregiver approach her birth.

How a suspected big baby impacts mum

Imagine you are at your obstetrician appointment and they make a comment about how big your baby is. Perhaps it is an off the cuff remark or maybe it is an in depth conversation about how ‘your baby won’t fit’.

Whether you had been feeling confident and positive about your birth until that point, or if you had been filled with fear, hearing those words ‘wow, that’s a big baby’ is likely to have an impact.

It can be frightening to hear your caregiver speak of a baby that is ‘too big’ and hear their concerns over your ‘ability to birth your baby naturally’.

The more you hear these messages, the more you believe them – and that’s when the fear and self-doubt sets in. If you are constantly being told that you will never be able to birth your baby vaginally, that’s what you will start to believe.

This fear and self-doubt can start to play out during your birth.

Fear and birth

When you are scared or fearful your body goes into ‘fight or flight’ mode, releasing stressor hormones (adrenaline). These stressor hormones can slow or stop labour altogether.

While we need some adrenaline at certain times during our labour, too much throughout labour can cause;

  • the sympathetic nervous system to direct oxygen and blood flow away from uterus and towards defence system
  • contractions to slow, become erratic or stop
  • oxygen to baby to be limited and cause baby to become distressed
  • a cascade of interventions in response to this

One of the biggest ways to help control your adrenaline during labour is to feel calm and confident and have confidence in your body’s ability to birth your baby.

How a suspected big baby impacts the care you receive


Often the mere suspicion of a big baby can change the way your caregiver provides your care.

Research has shown that the caregiver’s suspicion of a big baby can be more harmful that actually having a big baby.

In one study (Sadeh-Mestechkin et al 2008). women who were perceived as having a big baby (and went on to have one) had more than three times the caesarean rate, induction rate, and more than four times the complication rate (including perineal tearing) than those who actually had a big baby without the suspicion of it first.

According to the authors of that study

‘Our ability to predict macrosomia is poor. Our management policy of suspected macrosomic pregnancies raises induction of labor and cesarean delivery rates without improving maternal or fetal outcome.’

In other words – the intervention rates increase with a suspected big baby without improving outcomes for mum and baby.

Likewise, women who are told they have a big baby are more likely to choose an elective caesarean. (Peleg et al 2015)

Another study showed that when caregivers suspect a big baby, they are more likely to suggest induction of labour or caesarean section for stalled labour. (Evidence Based Birth)

Why the concern over big babies?

Let’s say you actually are having a big baby – what are the complications? Why does it matter?

The main reason cited for early induction of labour or caesarean section is shoulder dystocia. Shoulder dystocia is when baby’s head is born but one of their shoulders get stuck behind mum’s pubic bone, causing a delay in birthing their body.

Shoulder dystocia occurs in 0.7% of births (1 in 150 births).

According to the Royal College of Obstetricians and Gynaecologists,

‘Shoulder dystocia is more likely with large babies but nevertheless there is no difficulty delivering the
shoulders in the majority of babies over 4.5kg (10 lb). Half of all instances of shoulder dystocia occur in
babies weighing less than 4kg (about 9lb).
Ultrasound scans are not good at telling whether you are likely to have a large baby and therefore they are
not recommended for predicting shoulder dystocia, if you have no other risk factors.

There are no absolute ways to predict whether your baby will have a shoulder dystocia. It is more likely to occur if

  • your labour is induced
  • you have a BMI of 30 or more
  • you have had shoulder dystocia previously
  • you have diabetes
  • you have a long labour
  • you have an assisted (forceps or vacuum) birth

Note there is nothing in this list that says ‘suspected big baby’.

According to one study there is an small increased risk of postpartum haemorrage associated with a big baby. That same study cites ‘no statistical difference’ regarding severe perineal tearing associated with big babies. (Weissmann-Brenner et al 2012) In other words, there is no evidence that a big baby is associated with tearing – even though it is an often cited reason to avoid giving birth vaginally.

You’ve been told you’re having a big baby – now what?

Firstly, don’t panic! Remember, that measuring and predicting your baby’s weight is not an exact science! The only way to accurately determine baby’s weight is to put them on a scale.

Secondly, according to Dr Rachel Reed

Healthy well nourished women grow healthy well nourished babies

Thirdly, having a big baby does not automatically mean complications (as we’ve seen in the studies)

Finally – you can birth your baby! It is important to not let that self-doubt and fear creep in.

One of the ways we can do this is through the use of affirmations relating to your ability to birth your baby. Affirmations are positive self-talk that work by challenging and overcoming limiting beliefs and self-doubts.

During Hypnobirthing Australia classes we discuss  how affirmations work and learn other techniques to help you create a positive mindset and remain calm and relaxed during labour.

The affirmations below are a great place to start!

So remember – a big baby does necessarily mean you will have a big baby. Nor does it mean that interventions are required – international guidelines don’t recommend induction of labour for a suspected big baby.

And even if you do have a big baby – so what? You are perfectly designed to birth your baby.



Chauhan, S. P., W. A. Grobman, et al. (2005). “Suspicion and treatment of the macrosomic fetus: a review.” Am J Obstet Gynecol 193(2): 332-346

Sadeh-Mestechkin, D., A. Walfisch, et al. (2008). “Suspected macrosomia? Better not tell.” Arch Gynecol Obstet 278(3): 225-230

Peleg, D., Warsof, S., et al. (2015). “Counseling for fetal macrosomia: an estimated fetal weight of 4,000 g is excessively low.” Am J Perinatol 32: 71-74.

Shoulder Dystocia Published 2012 – Royal College of Obstetricians and Gynaecologists

Big Babies: the risk of care provider fear

Weissmann-Brenner, A., M. J. Simchen, et al. (2012). “Maternal and neonatal outcomes of macrosomic pregnancies.” Med Sci Monit 18(9): PH77-81.

Kate Vivian is a self-professed pregnancy and birth geek who is finally learning to embrace the chaos of having 3 kids. It was the birth and ‘bringing baby home’ experience of her first baby, and the overwhelming guilt that went with it, that led her to start Bright Mums – and create a world where Mums matter.

 A Certified Hypnobirthing Australia Practitioner, childbirth educator and postpartum doula, Kate works with Mums-to-be not only supporting them through pregnancy, and birth but also teaching them to honour themselves at a time when the world is telling them their baby is the most important thing.

With almost 2 decades in adult education, Kate has the ability to create a safe space, a non-judgey space. A place where Mums can relax and feel supported regardless of what their journey looks like. 

A keen traveller in a former (pre-kids) life, Kate dreams of the day her kids are big enough to take skiing and they can completely show her up while she is busy falling down mountains.

You can find out more about Kate or how Hypnobirthing Australia classes by clicking below.