How accurate is baby measuring during pregnancy?

posted 3 years ago in Pregnancy
Post # 3
3677 posts
Sugar bee

It’s not terribly accurate. Rebecca Dekker recently wrote a post on big babies at It’s addressing a slightly different issue from your question, but if you scroll down about 1/3 of the way down the page and read her section under “Assumption #2: We can tell whether a baby will be big at birth,” she summarizes the research studies on the accuracy of ultrasound and care providers’ measurements of babies in utero. The accuracy rates are … not high.

That said, though, it’s entirely possible to gain a lot of weight, feel huge, and still be carrying a normal or even a smallish baby (there are some examples mentioned in the Evidence Based Birth post). It’s just really hard to tell before you give birth!

Post # 4
11668 posts
Sugar Beekeeper
  • Wedding: November 1999

I don’t know how accurate it is but my sister was HUMONGOUS! I thought she was going to be having a 10lb baby for sure (doctor thought more like 8.5lbs) but he ended up being just under 7 lbs!  Then, my friend who was all belly and just a basketball sized bump had a baby that was over 8 lbs.

Post # 5
13168 posts
Honey Beekeeper
  • Wedding: July 2010

It really isn’t that accurate.  Doctors will try to estimate but there really isn’t much way to be able to accurately tell how big a baby will be before it is actually born.


Post # 6
66 posts
Worker bee
  • Wedding: June 2016

It’s not very accurate but aside from doing scans all the time it’s the best we have.
Measuring your tummy measures everything, you, your baby, the placenta and all the fluid so it’s not just baby being measured however the measurement of your tummy is coupled with a customised growth chart based on your height and weight and your first scan and then the measurement is plotted on the graph. As long as the baby is between the 10th and 90th centile and consitentally grows the professionals are happy however you’ll be sent for a scan if the midwife thinks your baby is too big 🙂 

I’m a training midwife in the UK 🙂 good luck with your pregnancy x

Post # 7
1118 posts
Bumble bee
  • Wedding: September 2012

From what I’ve heard it’s not very accurate.  I’ve talked to more than two friends who were told their babies were going to be way bigger than they actually were.  One friend was pushed to get induced early but due to her beliefs she refused, ended up having baby a little late and he was only in the 7 lb range!  They told her to expect over 10 lb baby.  I’m not saying they are always that “off” but just sharing the stories I’ve heard.

Post # 8
1208 posts
Bumble bee
  • Wedding: January 2004

I had an ultrasound done at 36 weeks and doctor estimated my baby would be “well over 8 pounds”.  She was just over 6lbs at birth.  

Post # 9
330 posts
Helper bee
  • Wedding: June 2012

My dr told me the measuring with the tape is to measure your uterus only, not the baby itself.  He also said that the further along you are, the more inacurrate the ultrasounds become when it came to measuring the baby.  I had my last ultrasound at 34 weeks and he won’t do anymore now (he did them so late because I am anemic).

Post # 10
1760 posts
Buzzing bee
  • Wedding: June 2013

My fundal measurements were right on the entire pregnancy. Had an growth ultrasound at 35 weeks and was told he was 6lbs 10oz with 1lb margin of error, and baby grows a half lb a week usually. Had him at 38w1d and he was 9lb 3oz. I only gained 14 lbs with the pregnancy too, so I wasn’t huge. 

Post # 11
2690 posts
Sugar bee
  • Wedding: November 2012

I wondered too.  My frist son was supposed to be around 7lbs but was 6lbs 13 oz.  They can’t really tell.  I am nervous this baby will be huge as I feel like a w hale but I look fine in the mirror.  I don’t know.

Post # 12
919 posts
Busy bee
  • Wedding: September 2011

I think it is pretty close!  Mine has been right almost every time and when it was wrong (twice) it was 2 cm off – which they say the fundal height can be 2 cm off in either direction before they are concerned. 

Post # 13
3677 posts
Sugar bee

@MrsB1015:  But has your baby been born yet? (I see your EDD is in July).

The OP is talking about how accurately fundal height measurements correlate with the size of the baby at birth (or, rather, how accurately predicted size correlates with actual size at birth). Accuracy levels for that are pretty poor.


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