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How accurate are U/S for sizing?

post #1 of 8
Thread Starter 
Well to make a long story short, I had an ultrasound done on Thursday (there was blood after I wiped..sorry if TMI) to make sure there was no rupture or previa from when I got kicked a couple of weeks ago. Anyway, there wasn't thank goodness but I couldn't help but notice that Finn is measuring 36-37 weeks. I am only 33 weeks. Now I know I have relatively big babies (ds1 was 8lbs7oz at 37 weeks and ds2 was 8lbs4oz at 38 weeks) so I figured Finn would also be atleast 8lbs. He is measuring 6lbs 13oz already! My doctor is wonderful and I know he will not push my EDD up (although, being pregnant is getting alittle tiresome).

I was just wondering if others have found the u/s accurate or way off?
post #2 of 8
I have heard that the u/s measurements for guessing weight can be up to 2 lbs. off in either direction. So I don't really place much value on those guesses. My sister just had a baby in April and the u/s estimated over 8 lbs. but she was only about 6.5 lbs. and was full-term, born only 3 days before her due date.
post #3 of 8
I think it is sooo hard to say and I know that ultrasound CAN be notoriously innacurate, up to two pounds off. And it seems that they normally overestimate weight, not underestimate it. That being said, I had a late ultrasound with my DS, at about 38 weeks, and it estimated him at 8.5 lbs. He was 8 lbs 14 oz at birth. So that was fairly accurate. With my DD they estimated her at about 8 lbs at 39 wks and she was 7 lbs 10 oz at birth. So again, fairly accurate. But a friend of mine from work had a late ultrasound that estimated her DS at 10.5 lbs, scared her into a cesarean, and he was only 8.5 lbs.

I was thinking, though, even if your DC is say, 6.5 lbs right now, that means that it is likely that he would be around 8.5 lbs at 38-39 weeks. Pretty nice size.
post #4 of 8
My ultrasound tech 3 weeks ago said that usually ultrasounds are +/- 15%. He said that one time that he knows of he made a BIG mistake. The day before delivery he told mom baby was over 10lbs, but ended up being 7.5. He has 15 years of experience and works for the high risk and the low risk doctor.

At 30 weeks they estimated my little guy at 4lbs 1ounce, and at half a pound a week that puts him at 5 lbs 9 ounce at 33 weeks.

I keep telling myself my body wouldn't grow a baby it couldn't birth. Positive thinking!
post #5 of 8
At 37 weeks my bf's ultrasound measured the baby at over 10 lbs. So they scheduled a c-section. He ended up being only 8 lbs. 1 oz. :
post #6 of 8
third trimester u/s can be way off.
post #7 of 8
In general I've heard they can be way off - they are supposedly pretty accurate early on (like if you have an early u/s if you're not sure of your dates) but vary a lot as you progress. Personally, mine have been quite accurate regardless of when they've been done - maybe I've just been lucky to have a good ultrasound tech!
post #8 of 8
Thread Starter 
Thanks for all the input ladies I guess I'll just take it with a grain of salt.
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