Baby Size Estimate at Anatomy Scan vs Birth Weight

posted 2 years ago in Pregnancy
Post # 2
7991 posts
Bumble Beekeeper
  • Wedding: February 1997

Oh, they absolutely cannot estimate within half an ounce. You do not currently have a big baby at all; indeed, you are almost right at “average”. My babies were always over the 100th percentile. At the before birth scan, they said they refused to estimate on babies larger than 10 lb – mine was 11-1/2 and two weeks early. 

In the vast majority of cases, they overestimate the size. You are barely over what the baby “should” be right now, so please don’t worry. You’re doing great!

Post # 3
3697 posts
Sugar bee

I can’t remember the exact weight, but if memory is right my baby was measuring pretty average at our 20 week anatomy scan. Toward the end of my pregnancy she was measuring a bit small, and she ended up being born at 6 lbs on the dot, so a relatively small baby. I ate like a pig in the second half of my pregnancy and gained 40 lbs total lol so in my case indulging my ravenous appetite did not translate to big baby. 

Easier said than done but I honestly wouldn’t worry at all about this. A difference of half an ounce is negligible. As you get further along, your doctors will have a better idea of whether you’re baby is on the “big” side or not, but it’s not something I’d worry about at all right now. 

Post # 4
9416 posts
Buzzing Beekeeper

View original reply
knotyet :  I don’t remember the exact weight but my daughter consistently measured ahead. They said they would have changed my due date if she wasn’t IVF! I was terrified of a huge baby but she came 2.5 weeks early and was a nice little 6lb 10oz. 

Post # 5
569 posts
Busy bee

They were pretty accurate in my case but I think the margin for error is high.  He was around the 25th percentile at birth and in his anatomy and growth scans.

Post # 6
843 posts
Busy bee

View original reply
knotyet :  I don’t think I was told the weight at the anatomy scan but at 37 weeks they told me baby was measuring 8 pounds 7 ounces which got me worried because I still had 3 weeks to go. I gave birth at 41+2 (4 weeks later) to a 7 pound 11 ounce baby

Post # 7
1627 posts
Bumble bee
  • Wedding: June 2017 - A vineyard

They went back and forth on my pregnancy. I was diagnosed with GD so they did all the scaring with OMG your baby is gonna be HUGE because you suck. Then I measured smaller than they expected and I had to have another ultrasound which acted like she was going to be big again. Especially when my due date came and went. I ended up delivering at 41 weeks and she was 7 pounds. Which I thought was pretty good considering all the terror they put me through about big baby. I was 6 pounds as a 6 week premie so it seemed about right.

Post # 8
8499 posts
Bumble Beekeeper
  • Wedding: August 2012

They told me my baby would be 6-7 lbs max and she was 7.5. They can be really off either way.

.5 oz at 20 weeks is nothing. Not every kid can be the perfect “average” or we wouldn’t have a percentile scale.

Post # 9
6292 posts
Bee Keeper
  • Wedding: September 2015

I’m not sure the weight of my daughter during my anatomy scan. However, she was measure a few days ahead. She was born at 38+3 weeks at 5lbs 15oz…. TINY baby.

Post # 11
551 posts
Busy bee

View original reply
knotyet :  I had  my anatomy scan at 21 weeks and 5 days and our baby boy was estimated to be 1 pound 3 oz. I know I’ll be having a “big baby” since hubby is 6’4″.

Post # 12
179 posts
Blushing bee
  • Wedding: November 2020

The anatomy scan is a very poor indicator of baby birth weight. Individual characteristics are hardly being expressed yet and the very large majority of healthy babies will be measuring “normally” at this time. When you get to 30+ weeks then we start seeing baby be “smaller” or “bigger” or we can see that baby’s thigh bone is measuring a week shorter than average because baby is a little shorter (and btw a week off on a thigh bone is completely normal and ok). 11 ounces at 19w4d is absolutely average. The average at 20 weeks is 12 ounces. 

Source- I am an ob/gyn ultrasound technologist 

Post # 13
2557 posts
Sugar bee
  • Wedding: October 2016

I’m small. 5’2″. Anatomy scan at 20 weeks was perfectly normal. Had my son at 37 weeks and he was 10 lbs and 23 inches long. Did not fit into newborn clothes. Had my daughter at 37 weeks as well; 7lbs 6oz and 19 inches. Just depends on the baby.

Post # 14
747 posts
Busy bee
  • Wedding: August 2014

I would not worry about a scan that early at all and you’re close to average anyway.

My son measured 2 weeks ahead at my 28 and 32 week scans. Then a week behind at 36 weeks. At 38+3 they estimated he was 7lb3oz. He was born at 39+2 weighing 6lb13oz. So my last one was pretty accurate, but there was lots of fluctuation throughout. 

Post # 15
630 posts
Busy bee

My baby was in the 98th percentile for everything at the 20 week scan, so will be very interested to see what size he/she comes out at!

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