Big Baby on Ultrasound in Singapore: Should You Consider Induction?
- Eng Loy Tan
- Oct 3
- 3 min read
Big Baby Concerns in Pregnancy
Many mothers are told during pregnancy that their baby looks “big” on ultrasound and are advised to consider induction of labour. This can be stressful, especially if the suggestion comes suddenly or without much explanation. But does a “big baby” on scan really mean you need to be induced?
What the Big Baby Trial (2025) Really Showed
A lot of current discussion comes from the Big Baby Trial, published in 2025. The study looked at whether inducing labour at 38 weeks for babies suspected to be in the largest 10% could make birth safer.
Nearly 3,000 women took part between 2018 and 2022.
Half were offered induction at 38 weeks, while the rest waited for labour naturally unless medically needed.
Main finding: Babies induced at 38 weeks had a slightly lower chance of shoulder dystocia (shoulders getting stuck).
However, the difference was small and not statistically certain in the main analysis.
When looking only at those who followed the study plan strictly, induction appeared to reduce the risk further — but still modestly.
Serious complications for babies were rare in both groups.
Key takeaway: This trial only applied to babies thought to be among the largest 10%. It does not mean that every baby above average size should be delivered early.
Ultrasound Baby Weight Estimates Are Not Exact
Ultrasound is a very useful tool, but when it comes to weight, it is only an estimate. On average, scans can be off by as much as ±500 grams (10–15%).
For example:
If your scan says your baby weighs 3.8 kg, the true weight could be anywhere from 3.3 to 4.3 kg.
This means:
Some babies labelled “big” on scan may actually be average-sized at birth.
Being above the 50th or 60th percentile on the chart is still within normal range. By definition, half of all healthy babies will be above the average line.
What Are the Risks of a Big Baby?
Most slightly larger babies are born safely. But when a baby is truly much bigger, there can be some added risks:
Shoulder dystocia (shoulders stuck after head delivery, usually managed safely by the birth team)
Birth injuries (e.g. broken collarbone, temporary arm nerve injury — rare)
Higher chance of caesarean section if labour progress is difficult
Maternal risks such as heavier bleeding or more severe perineal tears
It’s important to remember: these risks are not guaranteed. Many women give birth vaginally to larger babies without major complications.
Should You Consider Induction Just Because of a Big Baby?
The answer depends on your individual situation. Things to consider include:
How accurate is this particular scan?
How big is “too big” in your context?
Do you have other risk factors (e.g. diabetes, high blood pressure)?
What are the benefits and trade-offs of induction for you personally?
Questions to Ask Your Doctor Before Induction
How reliable is my baby’s estimated weight?
What are the actual risks if I wait for natural labour?
What are the possible downsides of induction?
Do I have other reasons, besides size, to consider induction?
Final Reassurance for Mothers
Being told your baby is “big” can feel worrying, but remember:
A scan estimate is not always exact.
The Big Baby Trial only applied to babies suspected to be in the largest 10%.
Most babies above average size are still healthy and normal.
You don’t have to rush your decision. Take time to understand your options and make the choice that feels right for you and your baby.
About the author
Dr Tan Eng Loy is a senior obstetrician & gynaecologist in Singapore with extensive experience in managing both low-risk and high-risk pregnancies. He believes in maternal-centric care, evidence-based practice, and ensuring mothers have the confidence to make informed choices about their birth plans.
👉 If you’ve been told your baby may be “big” and feel unsure about induction, you are welcome to book a consultation. Every pregnancy is unique, and the best decisions are made when mothers are fully informed and supported.