Baby Size Estimate at Anatomy Scan vs Birth Weight

posted 2 years ago in Pregnancy
Post # 16
Member
780 posts
Busy bee

An anatomy scan is so early I’d say there’s a next to zero chance it means you’ll have a big baby. As for the accuracy of scans in general, my understanding is that it depends on the type of equipment – but even the best of the best aren’t THAT accurate. I had a large number of growth scans with my MFM – so the most top of the line ultrasounds out there – because I was having twins. Baby A consistently measured smaller than Baby B. Guess which baby was 4 ounces larger? Baby A. 

On the flip side, as I was being rolled into the OR, my OBGYN looked at my belly and said: I think that’s 13 lbs of baby. Baby A was 6 lb 10 oz, Baby B 6 lb 6 ounces- 13 lbs on the nose. 

Post # 17
Member
514 posts
Busy bee
  • Wedding: August 2017

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knotyet :  at my 36 week ultrasound (high risk pregnancy so I had more frequent ultrasounds) my daughter measured at 6 pounds 7 ounces and was estimated to be around 8 pounds at birth. I went into labor just over a week later and she was born 6 pounds 1 ounce, (and healthy! Just petite!) so it wasn’t super accurate considering she had a little more time to grow in those 9 days. It’s reassuring to have a general idea of where baby is measuring, but understand that there is always wiggle room while baby is literally wiggling around in there! Congratulations!

Post # 18
Member
254 posts
Helper bee

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knotyet :  A scan I had 4 days before giving birth estimated my baby to weigh 2.6kgs. He was born 3.45kgs, so completely off. 

Post # 19
Member
1478 posts
Bumble bee

My baby has stayed in the 90th to 100th percentile and I’m very tiny (5 ft, 80 lbs pre-pregnancy). But my husband is a big guy. My doctor says it’s genetics–not necessarily about the weight (gain) of the mother. I try not to worry about it because I figure women have been giving birth since the beginning of time and babies generally conform to our bodies (by exiting earlier or staying within a certain size) or else how would anyone have been born prior to the medical interventions we currently enjoy? 

Post # 20
Member
257 posts
Helper bee

My baby’s anatomy scans showed him consistently big and he came out a very big boy. His scans were incredibly accurate. 
Also, I’m 5’4″ and my husband is 6’3″ and our little boy is incredibly long with a huge head. It had nothing to do with what I ate. And I lost all of my pregnancy weight immediately at birth, so yeah, some babies are just XL lol. Congrats and good luck on your bundle! 

Post # 22
Member
354 posts
Helper bee
  • Wedding: July 2017

My son was in the 95% for weight at the anatomy scan at 19w2d, he was born 40w4d and was 8lbs. I measured smal around the 35 week mark so I was sent for an ultrasound and the estimate of the baby’s weight was 7lb8oz which was clearly in accurate based on the actual birthweight. I don’t think the weight estimate at 20 weeks can tell you anything about how big the baby will be at birth.

Also, my SIL had GD with both her kids they were still only in the 6-7lb range at birth.

Post # 23
Member
3293 posts
Sugar bee
  • Wedding: July 2011

I had a scan at 36 weeks with my son and he measured 7lbs. He was born at 38 weeks and was 9lb1. Those scans aren’t accurate at all.

both my kids were big, my daughter was 9lb3. I had them both naturally with just gas and air for pain relief. Big baby doesn’t always mean a bad birth. 

Post # 24
Member
1247 posts
Bumble bee
  • Wedding: September 2017

I love this topic. For about 75% of my pregnancy my baby was measuring large. Over a pound at the anatomy scan! He was born at 40 weeks 3 days at 5lbs 15oz. So…not large at all lol 

Post # 25
Member
138 posts
Blushing bee
  • Wedding: October 2014

So interesting! I just had my anatomy scan at 18+3 and baby was approximated to weigh 10 ounces. The doctor came is an told me the baby wasn’t a “monster” baby (thought that was funny), but that he was in the 90th percentile. My husband was almost 9 pounds born 2 weeks early… I am definitely nervous to potentially delivering a bigger baby. We will see!

Post # 26
Member
113 posts
Blushing bee
  • Wedding: November 2018 - San Diego, CA

Definitely not accurate! Baby was measuring on track at 20 weeks, then at 28 weeks she was measuring behind suddenly, I had an ultrasound a few hours before they wanted to induce me and it was 4 lbs 8 oz… She ended up being 3 lb 12. Crazy! Dont worry about ultrasound size, it all varies and it’s only a guesstimate

Post # 27
Member
1919 posts
Buzzing bee

No way, Jose! My OB estimated my son at just under 6 lbs at 36.5 weeks pregnant and said he wouldn’t get to 8 lbs by birth… he was born a week and a half later and 2 weeks before his due date at 8lbs flat.

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