The Big Baby Trial: What It Really Means for Your Birth Choices
If you've been told your baby is "measuring big," you're not alone. It's one of the most common reasons given for recommending early induction in pregnancy. But thanks to a brand-new piece of research—nicknamed The Big Baby Trial (officially the INDUCE Trial, 2024)—we now have solid evidence that challenges the way this is being handled in maternity care.
Let’s unpack what this study found, why it matters (yes, even here in Australia), and what you should know before making any decisions about induction.
What Was the Big Baby Trial?
The INDUCE Trial (2024) was a large randomised controlled trial conducted in Sweden. It included over 3,200 first-time mums who were all told their babies were measuring "large for gestational age" based on late-pregnancy ultrasound scans.
Half the women were induced at 38 weeks, while the other half waited for spontaneous labour.
What Did the Study Find?
The results were eye-opening:
No difference in rates of shoulder dystocia, the main concern typically cited to justify early induction for suspected big babies
Higher intervention rates in the induction group—including more epidurals, instrumental births (like forceps or vacuum), and caesareans
No meaningful improvement in outcomes for mothers or babies
And perhaps most significantly? The trial was stopped early. Because the data was so clear, researchers ended the study before completion due to lack of benefit and evidence of harm in the induction group.
The Weight Estimate Was Wrong—A Lot
Even more striking, 58–60% of the babies in the trial were NOT macrosomic (over 4.5kg) at birth. These were babies who had been labelled as "too big" via ultrasound. The scans were wrong. More than half the time.
This isn't just a small error—it's a major crack in the logic behind using estimated fetal weight (EFW) to justify intervention. And it echoes what we already know from other research:
ACOG (2020) notes that ultrasound predictions of fetal weight have a margin of error of ±10–15%, and this accuracy worsens as pregnancy progresses.
A systematic review by Chauhan et al. (2005) found that ultrasound estimations are off by more than 10% in 70–85% of cases.
Research shows that suspicion of a large baby alone (without actual macrosomia) is associated with higher rates of caesareans and interventions, regardless of birthweight.
So when someone says, "Your baby is looking big," we have to remember: it's often based on a guess—and a shaky one at that.
How Is This Relevant to Australia?
Although this trial was conducted in Sweden, the findings are very applicable to Australian maternity care. Here's why:
Australian hospitals also rely heavily on ultrasound estimates to predict fetal size
Rising induction rates are a well-known issue in Australia, with some hospitals reporting rates over 40%
Many women here are told to consider early induction simply because their baby is measuring large—despite the evidence
Standardised population growth charts (rather than the UK’s GROW chart used in the study) are more common in Australia, but the issue is the same: questionable accuracy leading to unnecessary interventions
What About the ARRIVE Trial?
You might remember the ARRIVE Trial (2018)—a US-based study that suggested inducing low-risk, first-time mums at 39 weeks could slightly reduce caesarean rates. It was quickly embraced in many hospitals.
But unlike INDUCE, the ARRIVE Trial had very specific eligibility criteria, strict management, and took place in ideal clinical settings. It’s been widely critiqued for how quickly it was generalised into routine practice.
So now we have a high-quality trial showing no benefit to early induction for suspected big babies—and in fact, more harm. Will that be embraced just as quickly? Probably not… which is why informed parents and birth workers need to keep asking questions.
What Can You Do If You’re Told Your Baby Is Big?
You absolutely have the right to:
Ask how accurate the scan is, and what other information your provider is basing the recommendation on
Request more time to make your decision, especially if there are no other concerns
Decline induction if you don’t feel it’s necessary
Seek a second opinion
Learn about optimal positioning, upright birth, and how your pelvis makes space in labour
Remember: this isn’t about ignoring risk—it’s about understanding what’s actually risky and what’s just assumed to be.
Informed, Not Rushed
It’s easy to feel pressure when "big baby" becomes the centre of the conversation. But you don’t need to make big decisions based on a guess. You deserve time, information, and options.
This study is a powerful reminder that more intervention doesn’t always mean better outcomes. And that when we treat estimated size as a diagnosis, we risk turning a healthy pregnancy into a medicalised one without evidence to support it.
Stay curious. Ask questions. Trust your gut. And know that being informed is a strength—not a threat to the system.
Because birth decisions should be based on you, not just a scan.
Want more evidence-based info like this? Check out our birth education offerings at Birthability Birth Boss and get the tools to navigate your birth like the boss you are.
Read the trial here: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(25)00162-X/fulltext
