Is a 'big' baby a big problem?

Do you need to have an induction if you have been told your baby is measuring 'big'? What does the research say?

At my last group class, 3 of the 5 women were being sent for Growth Scans due to measuring 'big' - that is 60%! When this happens, the word 'induction' starts being thrown about. So what does this mean for you, and what are your options?

Reading your GROW Chart

Inductions are commonly offered because baby is suspected to be measuring very large but is this necessarily an issue? To understand this we first need to understand how growth is measured. Baby's growth is tracked using two methods, fundal height measurements using a tape measure, and ultrasound scans. These measurements are then plotted on graphs to track baby's growth against "centiles". Centiles are lines on the chart, showing where in comparison to 100 babies yours compares. Take a look at this growth chart:

If you have been sent for Growth Scans, you will be able to access your Grow Chart on the Badger Notes App. Your chart is unique to you, and is created taking your height, weight and BMI into account (despite BMI not being a accurate measure of health - but more on that another time!)

Inconsistent vs Consistent Growth

When considering baby's size and growth, one thing to consider is consistency. If your baby has always measured on 90th centile consistently, then it purely means baby is big and that's not necessarily an issue. If your baby started off just over the 10th centile and gradually climbed up the centiles to the 90th, that's an indication that potentially something is affecting growth such as unmanaged gestational diabetes, and baby is growing faster and bigger than they would normally, and that may be a cause for concern.

Generally we grow babies appropriate to our size and a consistently small or large baby just means they're small or big! If you're 6'1" and your partner is 6'2", you're likely to have a baby up nearer the higher end of the centiles, and that's not surprising! It's genetics! And it doesn't mean you won't be able to birth your big baby vaginally without issue either.

Another thing to be aware of is comparing scan measurements against fundal height measurements. These are not like for like and shouldn't be compared against each other. If you agree to extra scans, be aware that particularly in the third trimester these can be less accurate and a small or large baby may be incorrectly picked up because scans can be 15-20% out.

"Antenatal estimates of fetal weight are often inaccurate so many women may be worried unnecessarily, and many inductions may not be needed." Induction of labour at or near the end of pregnancy for babies suspected of being very large (macrosomia) - Boulvain M et al 2016.

So for a baby estimated to weigh 4kg (the cut-off point usually used to define a 'big' baby), a 15% margin either side means the range of the estimate is from 3400g (7lbs 5oz) to 4600g (10lbs 4oz).

What about shoulder dystocia?

Induction is often suggested to reduce the chances of shoulder dystocia. This is when after a baby’s head has been born, one of the baby’s shoulders becomes stuck behind the woman’s pubic bone, delaying the birth of the baby’s body.

This happens in about one in 150-200 births, depending on what data you look at. We think it might occur less often when women are able to move about freely, so that’s why the estimates that come from of hospital-based studies and obstetric researchers tend to suggest that it’s a bit more common than when you look at data from home and birth centre settings. But either way, it’s not an everyday occurrence, though it’s not a rare event either.

Being able to move freely is a cruical sentence here - if you are offered an induction it is likely you will be asked to be connected to a CTG monitor which can restrict your movement, therfore increasing the risk of shoulder dystocia on top of having a big baby.

Along with this, Dr Sara Wickham makes these Key Points in this article:

1. The vast majority of big babies (in fact 94% of those who weigh 4kg or more) won’t have shoulder dystocia.

2. Shoulder dystocia doesn’t only occur in big babies, it can occur in small babies too.

3. We can’t accurately predict which babies will be big as ultrasounds are inaccurate.

4. Only a few of the babies who have shoulder dystocia will have a serious problem anyway (and remember that only one in 150-200 babies have shoulder dystocia in the first place.)

5. Induction has risks and downsides which have to be weighed up against any possible benefits.

6. There may be other things we can do to prevent shoulder dystocia, like not having women laying on their backs to give birth and offering more freedom of movement.

More recent evidence from 2022 shows that scans cannot predict shoulder dystocia and that only one thing was associated with a higher chance of shoulder dystocia, and that was whether or not the woman had an epidural. Those who had epidurals were more likely to experience shoulder dystocia. And we know women who are induced are more likely to request an epidural (Newman et al. 2022).

What about the guidelines?

The NICE (The National Institute for Health and Care and Excellence which are used by the NHS) guidelines state that a suspected large baby alone with no other medical indications ISN'T a reason for induction. This is also echoed by the World Health Organisation.

NICE GUIDELINE: Suspected fetal macrosomia 1.2.24

Discuss with women without diabetes and with suspected fetal macrosomia that:

• the options for birth are expectant management, induction of labour or caesarean birth (see the NICE guideline on caesarean birth)

• there is uncertainty about the benefits and risks of induction of labour compared to expectant management, but:

• with induction of labour the risk of shoulder dystocia reduced compared with expectant management

• with induction of labour the risk of third- or fourth-degree perineal tears is increased compared with expectant management

• there is evidence that the risk of perinatal death, brachial plexus injuries in the baby, or the need for emergency caesarean birth is the same between the 2 options

• they will also need to consider the impact of induction on their birth experience and on their baby (see recommendation 1.1.3).

Discuss the options for birth with the woman, taking into account her individual circumstances and her preferences, and respect her decision. Support recruitment into clinical trials, if available. [2021]

What about the Scottish picture?

Have a look at the graphs below and you can make your own assumptions. Babies birth weight in Scotland is gradually increasing over time. It could be argued that the 4kg cut off for a big baby should be shifted to take account of population changes.

What is interesting about these graphs - and the reason I have included the induction and emergency c-section graphs - is that the percent of babies weighing more than 4kg in Scotland rises steadily until 2012 - where it begins to decline. If you look at the other two graphs, inductions and emergency c-sections really increase at this time. So I don't think babies are getting smaller - I think more people are being offered inductions earlier for big babies leading to the downward trend in the weight data. And I'm not sure this is right.

So if you are being offered an induction, what are your option?

Having a 'suspected' big baby should not change your options. They remain the same as they always did. You have the right to choose where and how you birth your baby.

If you want a home birth, you should still have this option.

If you want a water birth, you should still have this option.

If you want a hospital birth, you still have this option.

If you want an induction, you still have this option.

If you want an elective c-section, you still have this option.

What would I do?

Personally, I would research different positions for labour, learning different ways you can move will be crucial to help your baby descend through your pelvis without getting stuck. I would also learn and practise perineal massage from 34weeks to reduce the chance of tearing.

Induction carries its own risks and it is important to be informed of these. You increase your chances of complications by having an induction so I would decline this, at least initially up to a time I felt comfortable with, 41 or 42 weeks - then I may reconsider.

I would plan the birth I dreamt of, and learn alternate coping strategies for pain relief such as hypnobirthing, so that I could avoid an epidural.

Final Thought:

Don't let fear drive your decisions. Make sure you make decisions from an informed place that are right for you.

You can my blog post about alternative pain relief options here.

Or for more information on induction - head here.