Potential Big Babies: Understanding the Implications and Accuracy of Scans

Hearing that your baby might be "big" can stir up a mix of emotions — excitement, worry, confusion. It’s completely normal to feel unsure about what it all really means for your pregnancy and birth plan.

At Beyond the Bump, we’re passionate about providing warm, evidence-based guidance that leaves you feeling informed and empowered. Let’s walk through what you need to know about suspected big babies, scan accuracy, and how you can confidently navigate any discussions with your care team.

How Are Big Babies Suspected?

Often, the first indication that your baby might be "measuring big" comes from your fundal height measurement — that’s the measurement from your pubic bone to the top of your uterus, taken with a tape measure during routine midwife appointments.

It’s important to know that while fundal height can give a rough idea of baby’s growth, it's a very imprecise method. Factors like who is measuring (different midwives can measure slightly differently), the time of day, how much you’ve eaten, your position, your baby's position, and even bloating can all affect the number.

According to NICE guidelines, fundal height measurement is recommended as a basic screening tool, but if there are concerns (too big, too small, or growth slowing), you may be referred for a growth scan.

How Accurate Are Growth Scans?

The idea that growth scans can accurately predict your baby's weight isn't entirely true. According to NICE (National Institute for Health and Care Excellence) guidelines, late pregnancy scans can be off by up to 20% in either direction.This means a baby estimated to weigh 4kg could actually weigh anywhere between 3.2kg and 4.8kg!

It’s important to know that ultrasound estimates are just that — estimates. They’re useful for spotting trends (like slow growth or sudden increases) but less reliable for pinpointing an exact weight.

What the Research Says About "Big Babies"

The Royal College of Midwives (RCM) and NICE both emphasise that a suspected big baby alone is not a reason to offer early induction or caesarean section if there are no other concerns.Research shows that most larger babies are born safely vaginally — and many aren’t as large at birth as predicted!

It’s about your whole clinical picture, not just one scan result.

Questions to Ask Your Care Provider

When a bigger baby is suspected, it can sometimes lead to conversations about changing your birth plan. A useful tool we teach inside The Birth & Baby Academy is the BRAIN acronym — helping you make confident, informed decisions.

BRAIN stands for:

• Benefits – What are the benefits of any suggested intervention?

• Risks – What are the potential risks?

• Alternatives – Are there other options?

• Instinct – What is your gut telling you?

• Nothing – What happens if we wait and do nothing for now?

  
  

👉 Our free video, Taking Control of Your Birth, talks you through how to use BRAIN in real-life scenarios. It's a great starting point if you’re facing decisions about suspected big babies!

Building Your Confidence

Hearing that your baby might be "big" doesn’t mean something is wrong — and it certainly doesn’t mean you can’t have the birth you are hoping for.

Inside The Birth & Baby Academy, we have a full module on navigating birth choices, decision-making, and understanding scan results so you can approach your labour feeling calm, confident, and empowered.

✨ You deserve clear, compassionate information — and we’re here to support you every step of the way.

Final Thoughts

• Growth scans aren’t perfectly accurate — and your baby’s size doesn't define your birth.

• Bigger babies can and are born vaginally every day.

• You have choices, and asking questions can help you make the right ones for you.

• Trust yourself — you are already the expert on your baby.

If you're looking for more tools to feel confident in your pregnancy and birth journey, check out The Birth & Baby Academy or download our free video Taking Control of Your Birth today.