This blog is an excerpt from my Positive Induction Course, specifically the module on big babies. If you’re navigating decisions around induction for a suspected big baby, I hope this helps you feel informed and confident. Let’s dive into the evidence, challenges, and resources on this topic.

 

What Is a “Big Baby”?

The term macrosomia is used to describe a baby weighing more than 4kg (8.8 pounds) at birth. You might also hear the phrase “large for gestational age” (LGA), which means a baby is estimated to be above the 90th percentile for their growth at a particular stage of pregnancy.

The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) states this in their  “Diagnosis and management of suspected fetal macrosomia” guidelines:

For the purposes of this guideline, the definitions used are: • Suspected Fetal Macrosomia – Ultrasound Estimated Fetal Weight (EFW) and/ or Abdominal Circumference (AC) >/= 95th centile for gestation

But here’s the thing: estimating a baby’s size before birth is notoriously unreliable. Ultrasound predictions have a margin of error of up to 15%, so a baby estimated at 4kg could actually weigh anywhere between 3.4kg and 4.6kg. That’s a huge range! Despite this, these guesses often lead to unnecessary interventions, which can cause more harm than good.

 

The Real Risks of a Big Baby

Let’s look at the risks often associated with larger babies—and what the evidence really says.

1. Shoulder Dystocia

This is where the baby’s shoulder gets temporarily stuck during birth. While this can sound scary, the majority of cases are resolved quickly and without complications.

• 94% of babies over 4kg are born without having shoulder dystocia.
• Shoulder dystocia can also occur with smaller babies, and when it’s well-managed, it rarely causes long-term issues.

There’s also an ongoing debate about the value of third-trimester ultrasounds to detect macrosomia and prevent shoulder dystocia. A 2019 study by Wastlund et al. and a 2020 study by Moraitis et al. concluded that routine ultrasounds in late pregnancy didn’t significantly predict or reduce shoulder dystocia risks.

 

2. Increased Risk of maternal complications

Women with suspected big babies are more likely to be offered interventions like forceps, vacuum, or caesarean sections. However, it’s these interventions—not the baby’s size—that often lead to complications like tearing or postpartum haemorrhage.

3. Increased risk of blood sugar issues for the baby

Studies often group together healthy big babies and those born to mothers with uncontrolled gestational diabetes. It’s important to remember that healthy pregnancies with larger babies do not automatically carry the same risks.

 

 

Why Are We So Obsessed With Baby Size?

Dr. Rachel Reed and Dr. Sara Wickham have both written extensively on this topic. They point out that much of the fear surrounding big babies is based on outdated research. For instance:

• Historical definitions of “average” size were created when smoking in pregnancy was common, leading to smaller babies overall.
• Sara Wickham also highlights that our societal discomfort with larger bodies may influence this fear, perpetuating bias rather than evidence-based care.

 

Even the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) acknowledges that ultrasound predictions are limited in accuracy and don’t necessarily improve outcomes.

Interestingly, the research also shows that simply suspecting a big baby increases the risk of complications—even if the baby isn’t big. When care providers treat a pregnancy or labour as “high risk” due to suspected macrosomia, they may be quicker to intervene, which can lead to a cascade of issues like longer labours, higher rates of C-sections, and more assisted births.

As Dr. Henci Goer puts it:

“The inability to birth larger babies largely originates in doctors’ heads, not in women’s bodies.”

 

 

Why Birth Position and Movement Matter

I do wonder if the fear of big babies became more intense when women started to give birth on their backs and had their movement restricted in labour and birth.

One of the best ways to optimise the birth of any baby is to move freely during labour. Lying on your back reduces the space in your pelvis, which can make it harder for any baby to be born, let alone a bigger one. Positions like hands-and-knees, squatting, or side-lying can make all the difference.

Epidural may also have complicated things for a larger baby by further restricting movement.

If you’re planning an epidural, your birth partner or care provider can help you stay in positions that maximise pelvic space. Also gentle, physiologically paced pushing (rather than being directed to push) also gives the baby time to move and rotate, which helps during any birth, not just with larger babies.

 

 

Does Induction for a Big Baby Make a Difference?

One of the most common recommendations for suspected big babies is induction of labour. The idea is that delivering a baby early might prevent complications such as shoulder dystocia or birth injuries. But does the evidence actually support this approach?

The Cochrane Review on induction for suspected macrosomia and studies like the Big Baby Trial provide key insights into this question. The findings consistently show that induction doesn’t significantly improve outcomes for mothers or babies when it comes to suspected big babies.

Here’s what the research says:

1. Shoulder Dystocia

While induction may slightly reduce the incidence of shoulder dystocia, the absolute difference is minimal. Most big babies—whether induced or not—are born without complications. Importantly, induction introduces its own risks, such as longer labours and increased intervention rates.

2. Birth Injuries

Research shows that injuries like brachial plexus damage or clavicle fractures are rare, even in cases of shoulder dystocia. These risks don’t significantly decrease with induction. Instead, they are more closely related to the management of the birth itself, such as the use of forceps or excessive pulling.

3. Neonatal Outcomes

Studies like the Big Baby Trial found no significant difference in neonatal outcomes (e.g., Apgar scores or NICU admissions) between babies delivered after induction for suspected macrosomia and those who were not induced. 

 

Interpreting the Data

When studies Big Baby Trial conclude that induction makes no significant difference to outcomes, this can be interpreted in two ways:

1. A Justification for Intervention

Some care providers argue that if induction doesn’t worsen outcomes, it’s a reasonable option to offer. They may feel that taking action—even without clear evidence of benefit—is the right course of action.

2. A Reason to Avoid Intervention

While others take the view that if induction doesn’t improve outcomes, it’s better to avoid unnecessary interference. This perspective acknowledges the benefits of spontaneous, physiological labour and birth.

This difference in interpretation highlights a key question in maternity care: should we intervene “just in case,” or should we trust the natural process unless there’s a clear, evidence-based reason to step in?

Because induction is not without its own risks and challenges.

Such as:

• Longer and More Intense Labours: Synthetic oxytocin (Syntocinon/Pitocin) used in inductions can create stronger, more painful contractions, increasing the likelihood of epidurals.
• Increased Interventions: Induction often leads to more assisted births or emergency caesareans, especially in first-time mothers.
• Disrupted Physiology: Induction bypasses the natural hormonal processes that regulate labour, which can affect bonding, breastfeeding, and postpartum recovery.
• Prematurity: induction increases the risk of delivering a baby who isn’t yet ready for life outside the womb. They may have respiratory issues, feeding challenges, difficulty maintaining their body temperature and disrupted brain development (www.everyweekcounts).

 

My Personal Perspective on Big Babies

I admit, I have a soft spot for big babies—I’ve had three of my own. My first was 3.5 kg, my second 4.2 kg, my third 4.9 kg, and my fourth 4kg. My third baby’s shoulders did get a bit stuck during birth, but the midwives managed it beautifully, and she had no lasting issues. With my fourth, I agreed to an induction because I was worried about the possibility of shoulder dystocia happening again. At the time, I felt it was the right decision for me.

Looking back now, I might have made a different choice, knowing what I now know about induction and its risks. But every birth journey teaches us something, and my experiences with induction ultimately led me to develop tools and strategies for navigating it with confidence—tools I now share in my courses.

Big babies are not inherently a problem. Some babies are just bigger than others, and that’s completely normal. They’re simply beautiful, thriving little humans.

 

 

 

 

Celebrating Big, Beautiful Babies

In well-nourished, healthy pregnancies, many babies are simply big because they are thriving. In fact, 10% of babies born in Australia weigh over 4 kg—clearly, big babies aren’t as rare as we might think.

When supported to move, listen to their instincts, and birth in a physiological way, women’s bodies are incredibly capable—regardless of their baby’s size.

 

 

 

 

 

Key Takeaways

•Baby weight estimates are unreliable.

•Most big babies are born without complications, including shoulder dystocia.

•The risks of interventions often outweigh the benefits when the only concern is a suspected big baby.

•Focus on creating space and working with your body during labour to make the most of your pelvic dimensions.

 

Why This Matters

This blog represents one part of my Positive Induction Course, designed to help you make informed, evidence-based decisions about your care. Remember: guidelines provide recommendations for care providers—not mandates for families. You have the right to accept or decline any intervention.

So, if you’re carrying a gorgeous big baby, take heart. Your body has grown this baby, and it knows how to birth them. With the right support and trust in the process, you can look forward to meeting your beautiful baby—no matter their size.

For more on this topic, check out resources by Rachel Reed and Sara Wickham.