Growth scans in pregnancy: everything you need to know

Growth scans to track your baby’s size, weight and health are not uncommon. Here, we explain how they work and what they mean for you – plus what it means if your scan is at 28 weeks, 34 weeks, or 38 weeks…

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During pregnancy, there are 2 NHS scans that (generally) everyone will have: the 10 to 12-week dating scan and the 20-week abnormality scan.

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If you have a scan during your 3rd trimester, it’s called a ‘growth scan’ or ‘wellbeing scan’ – which is done to take your baby’s measurements, and assess their health.

In April 2019, researchers at the University of Cambridge also recommend that all pregnant women have an additional ‘breech scan’ at 36 weeks to check on the baby’s position. The NHS hasn’t acted on these recommendations yet, but we’ll update you if they do.

Here, we explain what a growth scan looks at, why you might be asked to have one, if you’ll have more than one, and what all this means for you and your baby…

Everything you need to know about growth scans

What is a growth scan?

Growth scans in pregnancy are done to monitor your baby’s health inside the womb, and check they’re around the right size for their gestational age.

Often they’re called ‘growth scans’ but also ‘wellbeing scans’. As Professor Basky Thilganathan, a Consultant Obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists (RCOG), explains to MFM:

“They’re not [technically] measuring growth. We don’t measure growth and there is no system by which we can accurately assess the growth – growth is speed, yeah? These are assessment scans, or wellbeing scans as we call them.”

These scans DO measure your baby’s size, though. Think of it as the next level up from your midwife measuring the size of your bump (your ‘fundal height’).

Why might I be sent for a growth scan?

“If you are having growth scans,” explains MFM’s favourite GP Dr Philippa Kaye, “it is because there has been a concern about how the baby is growing.

“Your midwife will measure your bump and if it is smaller than expected, they may recommend a growth scan. The scan is the same as the others and is an ultrasound.”

Reasons you may have an NHS growth scan include:

  • if your fundal height is measuring smaller or larger than expected for your baby’s gestational age
  • if your placenta is looking low at the 20-week scan
  • if you have diabetes or gestational diabetes
  • if you have a history of premature delivery
  • if you have a history of pre-eclampsia
  • if you have a condition like high blood pressure, or renal disease, that could potentially affect your placenta working properly
  • if you are very overweight, and as such there’s a possibility your placenta might not work properly
  • if you have a BMI of 40 or over. In this case, you’ll be having 2 growth scans during the later stage of pregnancy, as it can be tricky to do a clinic assessment
  • potentially, if there is a BIG difference in your height to your partner’s height (e.g. if one of you is very petite, e.g. 5’2″ and the other is extremely tall, e.g. 6’3″). The experts we’ve spoken to disagree on this one though – so we reckon it’s on a case-by-case basis!

You’ll also be asked to come in for a scan as-and-when, based on the presentation of certain symptoms, according to Professor Basky.

“A woman may present during the pregnancy with some symptoms, for example, they most commonly have:

  • concerns about the baby not moving properly
  • abdominal pain
  • vaginal bleeding
  • high blood pressure in pregnancy.

“These are things that occur unexpectedly during the pregnancy, where it is important for us to know that the baby is well and therefore a scan would be arranged,” explains Professor Basky.

Usually, it’s just a precaution. So, don’t panic, and don’t be afraid to ask your doctor questions, and share your concerns with them.

Nigel Thomson, Professional Officer (Ultrasound) for the Society of Radiographers (SoR) stresses that NHS growth scans are always done for a reason – you don’t need one unless you’re told you do.

“If the scan is being done on the NHS, it’s being done for a clinical reason. There is a reason why the scan is being done and therefore women really should ask: why do I need the scan? And speak to the midwife or doctor.”

When would I have a growth scan?

growth/wellbeing scan 2

These growth scans usually take place in the 3rd trimester of pregnancy. That’s why you might’ve heard them called ‘3rd trimester scans’. Usually, it’ll be after 28 weeks.

They’ll only be scheduled in if doctors want to be reassured that any symptoms, concerns about baby’s movements or risk factors aren’t affecting your baby’s health.

What exactly does the growth scan show?

During a standard growth scan, there are 4 or 5 things that will be looked at – according to Nigel:

  • your baby’s abdominal circumference
  • your baby’s head circumference
  • how long your baby’s femur (thigh bone) is
  • the fluid surrounding your baby
  • if needed, the blood flow in the umbilical cord

If you need other checks, they’ll be done during the scan, too.

This info is then compared to how far along you are in your pregnancy, and is then used to estimate your baby’s weight.

They’ll also be able to tell you if everything’s OK with the baby, and everything else: the fluid, the cord, and the placenta, etc.

When will I get my growth scan results?

There’s no reason why you shouldn’t be able to discuss the results of the scan with the sonographer or doctor at the scan.

Don’t forget: your caregivers should be giving you info you can understand, not confusing you. They should also keep you informed as to next steps, such as booking in another scan.

Nigel adds: “I think that anyone coming into scans needs to have them properly explained to them and the results explained.

“The outcome when they come out of the scan will be either:

  • the measurements are completely within the parameters you’d expect
  • the measurements may be smaller than you would expect and you’re going to rescan
  • the measurements may be larger than you would expect and you’re going to rescan.

“Everyone should be treated individually, as in, the scan results should be interpreted in the context of that woman and her size, ethnicity, etc – there’s various charts for those.

“It’s actually quite complex reviewing it all, but it should be reviewed.”

What is an individual GROW chart – and will I get one?

You may well be given or be aware of an individual growth chart for your baby, if you’re having multiple scans. Likely, this will be a GROW chart.

A GROW (Gestation Related Optimal Weight) chart is a “customised antenatal chart for plotting fundal height and estimated fetal weight”, according to Perinatal.org.uk

They’re part of a plan called GAP (Growth Assessment Protocol), which is all part of an NHS campaign to reduce the number of stillbirths across the UK.

All you need to know is that the protocol encourages use of a special chart for your unborn baby, designed around you and your personal situation, opposed to a one-size-fits-all approach used in the past.

Not every NHS hospital will use the software that creates these charts yet, but lots will, and hopefully, more will soon. In fact, this is a high-priority area for NHS England, says Nigel.

What’s the accuracy of a growth scan?

growth scan

Sonographers do pretty impressive techy stuff with these scans – and can use all these measurements they’ve taken to estimate your baby’s weight.

It is an estimate, though: it’s been reported in the past that there’s a 15% margin of error when it comes to weights determined by growth scans.

Measurements might be a tiny bit off, too, as they’re indicators. Yep, that includes your midwife’s fundal height readings and scans.

We know a lot of MFMers on our forum found this IRL. Glitterbug09 says: “My SIL was told she was measuring small to begin with and then she was told that her measurements were spot on.

“She then went into hospital at 36 weeks because she thought her waters had broken (they hadn’t) and was told she was measuring 3 weeks ahead!

“I don’t think it is an exact science to be honest… I doubt it is anything to worry about. My niece is perfect. She was a 9lb newborn xx”

Should I worry/do anything differently if I’m sent for a growth scan?

Please don’t worry if you’ve been asked to go for a growth scan. More often than not, the scans will show nothing wrong, and it’s just being done as a precaution.

“On the whole, the vast majority will have a perfectly healthy straightforward pregnancy, and these wellbeing scans are being done to reassure us that despite whatever risk factors they have, that their baby’s health is all going to be well,” says Professor Basky.

“It’s a way for us to screen out, pick up, the few babies that may have a problem. They’re being done to reassure the woman, and the doctor, that everything’s OK.”

If your scan anxiety is at an all-time high, remind yourself: your baby’s being monitored closely – which is a good thing.

On the off-chance something’s not right, your docs can use this knowledge to recommend the best possible course of action for you and your baby.

How long will my growth scan take?

A growth scan will take anywhere between 10 minutes to 30 minutes, depending on your baby’s position at the time of the scan.

It might also take 10 or so minutes for any results to be written up and shared with you.

Note: you should factor in typical hospital wait times, as well (you know your local hospital better than we do!)

I’m having growth scans every week or every couple of weeks – why?

Multiple growth scans in your 3rd trimester mean doctors need to keep a close eye on how your baby’s growing. The reason why, again, depends on you and your pregnancy.

It’s not very likely you’ll just have one scan, says Nigel. He says you could have anywhere from 2 to up to 8 or 9 scans.

We know the frequency can be a real worry for expectant women, though. Remember: it’s not bad that your baby’s being monitored so closely.

Do I need any other 3rd trimester scans?

growth scan

As mentioned earlier, typically you’ll only be offered 2 NHS scans, at around 12 weeks (your dating scan) and 20 weeks (the abnormality scan).

So, if there’s no cause for concern, you won’t *need* other pregnancy scans in the 3rd trimester.

If you do end up being scanned again, the sonographer and your doc should explain what the purpose of the scan is, and what it’s showing, and what the results mean.

Growth scan at 28 weeks – what it’s looking for

We know a fair few mums who’ve had growth scans at around 28 weeks – often it’s because their bump is measuring small.

This scan will take your baby’s measurements and compare them to the ‘average’ weight for babies at 28 weeks’ gestation. However, the scan may also be tailored to you and your baby.

Once you’re done, you may find that’s the only growth scan you need. If not, you may be asked to come back to keep an eye on the progress of your baby’s growth.

Growth scan at 34 weeks – what it’s looking for

Usually, this scan will also be looking for your baby’s measurements. It could be a follow-up to your earlier scan, a first time growth scan or one of many.

It could be because your baby is either measuring too small for the 34-week mark (on average), or a bit larger than expected, or due to other risk factors.

All of this depends on your personal situation. Whether or not you need to keep having growth/wellbeing scans will be determined as your pregnancy progresses.

Growth scan at 38 weeks – what it’s looking for

Between 36 and 40 weeks, a growth scan can be done in the run up to your due date.

This scan will again take your baby’s measurements, and make sure everything’s on track for you to deliver your baby as planned.

You’ll find out after this scan if your doctor thinks you should deliver your baby a few weeks early, due to their size.

Can I pray privately for a growth/wellbeing scan? How much are they?

If you haven’t been asked to come in to your local hospital for a growth scan, that’s not a bad thing! It means you don’t need one.

Docs don’t think they need to keep an extra eye on  things – as everything appears healthy, and you’re not prone to any risk factors.

That said, yes, you can book a private scan at any point during your pregnancy. Costs will vary, but expect to pay up to £90 per private scan.

SoR’s Nigel also advises you make sure you’re being scanned by someone who’s properly qualified, and can interpret the results correctly.

“If someone’s going for a scan in the independent sector – which is fine, there’s nothing to stop them – they need to ask who’s doing the scan, and are they qualified? What will happen? Will I be referred [on to the NHS]? Who’s gonna be doing my scan, basically?”

P.S. You may want to check out our guide to 4D scans in pregnancy before you book ?

Share your experience

Did you have growth scans in pregnancy? Maybe you’re expecting now and you’ve just found out you need one? Please do tell us your story in the comments below!

Images: Getty Images

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