Inaccurate Growth Scans

[YfenniChristie]

Hopefully this is the right place to post this. DS was born over a month ago by emergency c-section following a failed induction.

The week before his birth we had a growth scan. This placed him at roughly 8lbs and on the 20-something centile. However when he was delivered, he weighed 5lbs 14ozs and placed on the 2nd centile.

Everyone was surprised - one midwife said she'd never seen such a huge inaccuracy with the growth scan before. I'm hoping to have a debrief in the coming weeks and I'm hoping this is one of the many things they can shed light on.

I was diagnosed with pregnancy induced hypertension about six weeks before the birth, and was put on labetemol - it was suggested in the days following the birth that this could be a reason, but this doesn't explain the inaccuracy of the growth scans. And it's bugging me.

Basically I'm wondering if anyone else has had a similar experience and what (if any) were the reasons given behind it?

I’m surprised at people’s shock - I have always heard that growth scans are notoriously inaccurate.

I've never known a growth scan to be right. Does it really matter that they got it wrong?

My friend was induced due to a large baby. I was told mine was small. They were born a near identical and very average size.

A friend of mine was told all throughout her pregnancy that her baby was measuring really small, she was even sent to see consultants at a specialist hospital for more scans to monitor his growth. Right up until when she was in labour they kept saying how small he was going to be....

He was 9lb 5oz!!

My growth scan 5 days before I gave birth was 9lb 10os- I packed loads of 0-3 size clothes and not many new born in the hospital bag

DS was only 6lb 13oz - I've never known a growth scan go be right

Both of my scans were completely out, my "big" baby was 6lb, and my "small" baby was tiny leading to consultant lead care....he was 8lb 13!
I don't know why people take it as truth, it's a guess at best!

Ultimately it doesn't matter - DS is healthy and doing really well - I'd heard growth scans were inaccurate but I wanted to hear about others experiences.

I think it's bothering me because I was 39 weeks when I was induced and was on the receiving end of lots of "is he prem? comments from (well meaning) staff during the 3-4 days I was in hospital following the birth. I'd had regular growth scans from 20-something weeks, which all came back normal, and just can't understand how nothing was picked up.

I was told at 39weeks my dd was measuring at 11lbs gave birth at 40weeks to a 6lb baby.

Growth scans are notoriously inaccurate. I had a similar experience to you, was told my daughter would be 8lbs but was actually tiny, on the 2nd percentile!

I've been having growth scans with this baby due to DD being small and just today have been told baby boy has dropped from the 90th to the 60th percentile, so basically I've gone from being told to expect a big baby to being told he's pretty average. I'm trying not to put much stock into their predictions though!

Growth scans are causing me some anxiety! 😣

I've had a pretty straightforward pregnancy so far, routine growth scans due to raised BMI.

32 weeks baby was measuring on 55th percentile so bang smack in middle. No concerns.

A month later at 36 weeks she'd gone upto 90th percentile with her femur length measurement in 95th putting her estimated weight at 7.2lbs. Consultant sat me and my husband down and explained to us that if she continues this trend its likely they would want to induce me early to help manage risk of shoulder dystocia etc.

Then yesterday at 38+5 (39 week scan ish) she's measuring on 90th trajectory with femur length still in 95th and now an estimated 8.1lbs. However different consultant now saying fine to continue to term and overdue 🤷🏼‍♀️

I've heard growth scans can be out 1-2lbs either way, so if she's above by 2lbs already she'd be 10lbs already with a week until my due date and possibly allowed to go to 42 weeks 🤔

I have mild swelling (and what I think is carpel tunnel), borderline high BP but no protein in my urine so rules out Pre eclampsia at the moment but I'm struggling to understand now how two consultants can have such differing views. It's left me really confused.

Spending my last weeks of what's been a nice pregnancy, now really anxious about the birth and risks associated with if she is a big baby but also reading how often wrong they get it from the growth scans causing people unnecessary worry 🤦🏼‍♀️

I have booked a stretch and sweep tomorrow at 39 weeks to try move things along 🤞

Seems growth scans are all over the place and difficult to trust but Drs use them to manage our care appropriately so it's shocking how out of range they can be!

I was having regular growth scans and at weeks 37 weeks I was measuring at 7lb 8oz which was accurate from my 2 pre growth scans they predicated 8lb 8oz baby for 39 weeks as I was having an ELCS I gave birth by section last Thursday to my little boy at 10lb 15oz !! No one seen it coming no GD my levels at test we’re perfect. I don’t think the growth scans are accurate st all

The growth scans involve taking certain measurements (head circumference, abdominal circumference, femur length) and then using these to estimate overall size. So it really is an estimate even if they get each of those measurements 100% accurate. With my DD they were out by almost a kilo!

I’d say the first consultant wasn’t being particularly logical. The centile plotted on your growth chart is made up from three difference measurements (head circumference, abdominal circumference and femur length).

What was the abdominal circumference of the first scan with accelerated growth? Gestational diabetes wouldn’t lead to accelerated femur length, it would be increased AC. Second consultant appears to be applying this logic.

A consultant once described growth scans really well to me... he said:

You think they seem extremely accurate as if you are holding a tape measure from point to point. But in reality it is like eyeballing two spots on a wall across the room and guessing by eye the distance between them.

If you think about how much they pull on your new born to get an accurate length... they can't do that in the womb. Baby can be lying in a million positions and they have to make a best guess. It doesn't make sense to me that they are consistently wrong but I wish they'd explain to women that they are not that accurate instead of making out they can be taken as gospel.

There are lots of things that affect the accuracy of a growth scan - for example the amount of fluid around the baby, the position of the baby, the gestation at which the scan is down, the BMI of the mother, whether the mother carries most of her weight on her tummy or elsewhere, the tissue density of the mother ... you get the idea. They aren't perfect and should never be taken in isolation. A suspected small baby that is moving well, growing consistently in a healthy mother for example is different to a suspected small baby in a mum who smokes, that is not moving well, and the mum has a high BP. They are just part of the puzzle basically.

Was the estimated 8lbs for the day of the scan? Or was it an estimated birth weight if he was born on his due date and continued to grow at the same rate? As that also makes a significant difference.

I hope you are recovering well and your baby too.

I don't know if this helps at all but the estimated and actual birthweights are audited. There are targets to reduce the number of missed small babies (under 10th centile). So if there are a high number of these then they will look at why.

It also means in any future pregnancies you will be monitored more closely, recommended to take Aspirin etc.

They’re known for being inaccurate. I had a lot of scans with the consultant with DS and he was predicted to be about 6.5lbs at 39 weeks which when i had my section booked for. Even the consultant called that as unlikely since his sister was 7lb14 at the same gestation, low and behold DS was well over 8lbs.

I was advised with ds1 to be induced at 40 weeks following a growth scan, purely as he was measuring just under 6lbs (which seemed fine to me and DH as despite him being 6'6 he was 6lb when born, and I was also 6lbs but I was a nervous first time mum so I blindly trusted the growth scan results with no questions asked) There was nothing else wrong - no problem found with the cord etc it was just his small size that was apparently concerning (despite steadily following centile lines etc)

I was given a sweep first and then booked an induction for 2 days later if the sweep hadn't triggered anything.
I didnt need to be induced in the end as the next day he was born 7lbs 13oz - long and skinny like his dad, but perfectly healthy and obviously much bigger than the predicted 6lbs the day before.

It was 22 years ago now but i was induced 10 weeks early as i had no bump and the growth scans said that he was tiny and failing. They decided that he would be better off out than in.... He weighed 3lb 12oz at birth and was huge for that gestation! Growth scans arent the whole picture. Also other consultants said they would never have induced that early, this one did. I suppose it is all down to the individual doctor and their experiences as well as the scans.

Mine was just a few ounces out