Growth Ultrasound....How accurate?

KristiKubic · April 2014

I am 35 weeks tomorrow with my first pregnancy (a boy) and they have guessed I have a big boy most of my pregnancy due to my husbands size and his 20 week ultrasound he measured in the 63rd percentile. I measure right on track and have only gained 25 lbs up to this point. My doctor is not overly concerned and feels he will just be a bigger baby however every time I get an ultrasound, they are the ones who seem to be concerned that he is so big. So they did a growth ultrasound yesterday and they are estimating him to be 6lbs 12oz at almost 35 weeks and that his head is measuring at 37 weeks. I am not surprised and I have planned for a 9lbs baby the entire pregnancy again my husband is a big boy, 6"2, 250, broad shoulders, played semi-pro football.....big boy. They say these ultrasounds can be a +/- 1 pound but either way that would put him between 6lbs-7lbs.

Has anyone else had this done and if so what are you doctors saying? Just curious how much stock I should put in this or not. Right now I am not concerned or worried about him being big since I have planned for this. Just wondering if others have gone trhough this.

24karat · April 2014

As you mentioned, they can be notoriously off...not just +-1lb, it can be off by even more. For that exact reason my OB never encourages induction or an earlier c/s based solely on a 3rd Tri growth scan.

FWIW, my DD's growth scan at 39wks came back with an estimate just shy of 9lbs. She was born 6lbs 14oz over a week later.

dogsombrero · April 2014

My boy measured 7 pounds at 33 weeks I have a repeat scan next Tuesday to see if it was just a growth spurt or how large he is. With that said they are predicting a 9 pound baby based on his size, which while big isn't really abnormal or huge.

boymomstrong · April 2014

My son was very long! At my last scan he was estimated to be ab 9-10 lbs, i was also prepared for this as my husband is large too! 6' 3" 215lbs and broad! Well imagine my surprise when my tiny 7lbs 1oz son was placed in my arms!

it will be what it is, but my doc did say the estimats weight based on length, and my son was long! So far this baby is on the HUGE side too! So we shall see what happens in 18 more weeks..

beachbride5 · April 2014

first of all, why would they consider the 63rd percentile to be large? that's is just above the middle of the road. seems silly to me.

i have had growth u/s with all of my littles due to the way i carry- with my son, on his induction day (40w3d) they assured me he was "well over 8lbs" and he came out 7lbs even. with my daughter, they said she was 5lbs11oz at 38w and was born at 39wks 5lbs15oz, so hers was more accurate. with this baby, they said she is in the 50th percentile for weight at 3lbs14oz (31wks) so she is on track to be between 6-7lbs fully cooked.

so, long answer to your question is that they can be very wrong with their estimates but i don't see anything in your post that would be cause for alarm or indicative of a problematically large baby. trust your dr.

your baby boy might not go 40wks and end up below 8lbs. don't worry, mama, as long as you are being healthy, i'm sure you will be fine.

naturaloaklandmama · April 2014

I haven't had one of these growth ultrasounds but my midwives keep telling me that I am measuring between 2-3 weeks ahead (not sure on size as they just measure rather than do US -- my last one was the anatomy scan at 20 weeks where I didn't get a percentile but they said he was right on track). In any event, they are concerned that I am growing a big baby and have advised me to cut back on sugar. The thing is, I don't have GD, and the only sugars I am really ingesting are fruits -- though admittedly, I have been eating a lot of fruit to cut my sweet tooth cravings in lieu of candy, cupcakes, or cookies (though I do probably indulge in one of those about once/week). I know this is slightly unrelated to the post BUT it just seems silly to me and counter to good nutritional advice to tell someone to eat less fruit. I did read online that sugar can lead to big babies BUT I also saw that the advice is to swap fruit for sweets... Has anyone else heard anything along these lines from their docs or midwives?

baloneydisc · April 2014

DD's was pretty close. The last estimate they gave me was 7.5lbs (based off an u/s at 32w). She was 6lbs 14oz at birth.

ncbelle · April 2014

They aren't very accurate. And it's not something I'd worry at all about (although my last baby was 10 pounds).

jnnfrrose6 · April 2014

I didn't have a growth ultrasound with DS, but I also expected a big baby. DH sounds similar to yours (he's closer to 6', fluctuates between 200-230 depending on his work out routine, and also played semi-pro football). We were both also bigger babies, so I just expected DS to be big too. He was 6lb 14oz. From everything I've ever heard, the growth u/s aren't really that accurate and many doctors are actually moving away from them. I wouldn't worry too much about it.

Aliki · April 2014

Why would 63rd percentile be considered a "big boy"? that sounds average to me.

My ultrasounds were accurate-- I had one at 20 weeks, 35 weeks, and 39 weeks-- all three times, she measured in the 90th percentile.

At the 39 week appointment, they estimated she would be 9 lbs 8 oz at birth.

She was born 40w1d at 9 lb 10 oz. Only 2 oz off.

LUCKY22 · April 2014

With DS they were hoping to get him up to 5lbs before I delivered (at 36w6d). He was 7lb.

jldcjs · April 2014

Anyone know why they aren't accurate? I could see weight being off, but it seems like limb length and circumference are easier to get actual measurements, but I don't really know.

artroyer · April 2014

I feel like it probably depends on the equipment and the tech too... a lot of people do have stories of the measurement being off, and it's by no means definitive, but for us it was right on for our first. They estimated her at 8lbs at 38 weeks and she came two weeks later at 8lbs 15oz. If you figure that they gain 1/2 pound a week at the end, it was pretty accurate.

I actually just had a growth scan yesterday at 35w1d and they estimated 5lb10oz. I guess we'll see when she comes out! They told us she was 53rd percentile (but online charts say 30, so it depends where you look too) which is much smaller than my first so I'm hoping for a baby way less than 9lbs this time haha.

Justabean3 · April 2014

With my first my belly was huge and they thought he was going to be big. I went in and was shocked. He was 3rd percent at 38 weeks around 3.5-4 pounds.

I went it at 39.5 weeks and he was over 5. The lady told me he didn't even look the same and you can visually see the difference in his cheeks.

At 40.5 weeks he was 6 pounds He came at 41.5 weeks and was just at 7 pounds.

You never know how much or when they will grow. The ultrasound was less than 1/2 a pound on mine.

Why did I get so many scans? They wanted to let him cook as long as possible to catch up

cookieinva · April 2014

FWIW when pregnant with my son I measured perfectly on-time and "normal" size all along. He was over 10 lbs at birth.

AbbySeiden · April 2014

I'm going through the exact same thing. At 33 weeks my belly is measuring at a 37 week size, and my baby boy is measuring in the 91st percentile for size! The doctor also said I have a generous amount of fluid, so even though I passed my initial one hour glucose test they're having me repeat it this weekend just in case. They told me he's tracking to be a 10lb-er! So I have another ultrasound scheduled for two weeks. My husband is a big guy but I'm only 5'4" and I'm terrified!

momthatlifts · April 2014

A friend of mine just had her son who was measuring a week ahead her entire pregnancy. At 39 weeks she was certain she was going to have a huge baby. He ended up coming out at 7lb and some oz.

greeneyed_bride · April 2014

They thought my son was going to be large based on both fundal height and two growth ultrasounds. I heard an estimate of "over nine pounds" from two different OBs. He was 8lb 7oz.

ETA - my fundal height was measuring 4 weeks ahead pretty much my entire third trimester.

rockopera · April 2014

I measured ahead quite a bit as well. At 35 weeks, they estimated he was 7.5 lbs. At 38 weeks, they estimated he would be about 10 lbs.

I was induced at 39 weeks (for hypertension) and had an uncomplicated vaginal birth. Baby was 9 lbs, 9 oz. The estimate was pretty close for me.

chillypenguin · April 2014

I had a growth scan with DD2 three days before she was born. They estimated she was 7 lbs 6 oz, she came out at 7 lbs 11 oz.

Nekotaru · April 2014

I have to be checked weekly because of polyhydromnea now but at 34w my girl's head was measuring at 38w and they said she was 5lbs 11oz but *admitted* to me they can be off by 2lbs on a normal basis (because I asked about that). They assume when she is born she will be 8-9lbs and keep telling me she will be a "big baby" but they asked if my husband or I were big babies and we were not. He is only 5' 10" and I am 4' 11" - we are not even big people lol.

So, I am willing to bet they are off a bit, but all I can do is wait and see. I believe I have only gained about 25lbs total as well, and do not have GD.

jenb_99 · April 2014

It depends on a lot of factors -- the power of the machine, the angles the tech is able to shoot, the number of measurements the tech uses in his/her calculations, etc. -- but yes, a growth scan can be very accurate.

The ultrasound tech at my OB's office has a crazy high accuracy rate for late-third-tri scans. The one she did for DS at 38w3d was nearly dead on. The scan told us he weighed 8 lb 10 oz at that time and had about another pound to grow. Sure enough, when he came at 40w2d, he weighed 9 lb 7 oz.

BeesKnees181 · April 2014

Aliki said:

Why would 63rd percentile be considered a "big boy"? that sounds average to me.

My ultrasounds were accurate-- I had one at 20 weeks, 35 weeks, and 39 weeks-- all three times, she measured in the 90th percentile.

At the 39 week appointment, they estimated she would be 9 lbs 8 oz at birth.

She was born 40w1d at 9 lb 10 oz. Only 2 oz off.

This. And percentiles are based on a bell curve, where the most amount of folks fall in the middle - where the curve is at its tallest. It is the tails of the curve that cover sizes that are smaller/larger than what occurs at higher rates, and even beyond that most OB's are only concerned when you fall into the 3rd and 97th percentiles. Percentiles mean nothing about being better or worse off...it is only a measure of where your baby falls in comparison to all the other babies out there. As for your question - I am a FTM so I have to wait until these babies are born to see how accurate my growth scans are.

Jodash24 · May 2014

The week before my induction baby was 7lbs on the scan, so dr estimated around 7.5 lbs, he was actually born 8lbs 15

Dianakdee · May 2014

They said that my baby was going to be close to 9lbs at my growth. Ultrasound and that my baby was measuring bigger but he turned out to only be 7lbs 2oz.

jess9802 · May 2014

The last U/S I had with DS was at 37w6d, and his estimated weight at that time was 8lbs, 1oz. He was born at 39w3d, and he weighed 7lbs 14.6 oz. While the weight estimate was off by quite a bit, the head size was pretty dead on.

My SIL had an U/S at 37w5d and the estimated weight was 8lbs, 8oz. My nephew was born the next day and weighed 8lbs, 9.6oz.

PrimRoseMama · May 2014

Growth estimate on DD was 7 lbs in 2011. She was 5lbs 11oz

Growth estimate on DS in 2013 was 9lbs. He was 7lbs 11oz.

Basically take the estimate & it can go 2-3 lbs in either direction.

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