Ultrasound weight vs real weight

I'm getting into the end of my pregnancy now, I'm at 34 weeks with my girls and we just had an ultrasound Friday. Baby A was measured to weigh at 5lbs 5oz and Baby B was measured to weigh at 5lbs 9oz. I was happy to see that they were over 5 lbs, in the upper 50th percentile for their age and they're pretty much even in their growing.

My main question here though is how off do these measurements tend to be? I know they obviously can't be 100% by any means but are they more or less accurate? Should I be worried about a very large difference if they were to be born this week?

 

I am not sure about twins but i know in my past pregnancy with my 18 month old they were way off on his weight. They had told me that he was no more than 5 lbs and only 15 to 16 in long with a growth retardation. They took him a week early becouse no growth and low and behold he was delievered and weighed 7 lbs 7 oz and was 18 inches long thank God . My doctor was so shocked that the ultrasound was so off. I hope that with this pregnancy they are right. I am now 33 weeks and both of my baby boy's are measuring 4 and 1/2 lbs each so i'm crossing my fingers !!

 

I had an u/s on a Monday and A weighed 4lbs 9oz and B weighed 4lbs 12oz. I delivered them on that Friday and they A was 4lbs 8oz and B was 4lbs 10oz....so for me they were pretty close

 

I got my last ultrasound at 34 weeks, and based on that both the boys were somewhere around 6lbs. My boys were born 4 weeks later, and their projected birth weights would have been about 7 lbs- 7lbs 8 oz. Well, one was 7lbs 3 oz and the other was 6 lbs 5oz. They were spot on for twin A and off a pound for twin B.

Now it's possible that my twin B just slowed his growth dramatically. I have seen studies that suggested twins carried to term (38 weeks or greater) have similar weights as singletons through the earlier parts of pregnancy, but they experience much less grow in the last month or so as the uterus reaches it's maximun size (and it gets crowded in there ).

 

For me they were way off. The day before I deliverd at 36 wks, baby A was estimated to weigh 6.5 lbs and baby B was 5.4 lbs. Everyone was surprised when they came out at 5.2 lbs (A) and 4.1 lbs (B). Both were 17 inches. We delivered a week earlier than scheduled because baby B's growth had slowed alarmingly. Neither baby required any NICU time. Up until that last ultrasound they always measured within a couple ounces of each other. Best wishes. Sounds like your babies are pretty nice weights already for 34 wks.

 

I had my last U/S at 36 weeks and they were determined to almost 7 lbs at that time. At birth both were 1 lb less.

 

I think they're more often wrong than right, especially when estimated large. Mine were spot on though. They measured lower 6lbs range at 34 weeks (they were growing a little less than 2lbs in 4 weeks) and at birth (4 weeks later) they were 7lbs110z and 7lbs10oz ... so pretty accurate. They were estimated to measure about 2 weeks ahead and they were born at average singleton sizes 12 days early ... seem right to me!

 

I think it really depends on the circumstances. The quality of the u/s machine used and the abilities of the person performing the u/s can come into play as far as accuracy goes. Just clicking the tiniest bit in one direction or another can change the results quite a bit.

I had an u/s done the night before my girls were born and they told me that Baby A weighed 2lbs even, and Baby B weighed 2lbs 8oz. You can see from the stats in my siggy what their actual weights were when they were born.

 

I had an u/s the day before my girlies were born. They said Sydney was 7#7oz and Sabrina was 5#5oz. When they were born the next day, they were 7#9 and 5#3. So they were both off by 2 oz, one more and one less. Pretty close, IMO.

 

Our doc told us an no more than 8 oz either way in his office. We had the u/s on Friday delivered on monday. Jazz was right on but Jessy was 6 or so oz to heavier. I'd much prefer heavier than lighter

 

Hard to say how off mine were because I can't remember exactly, but I think they told me at 37 weeks that my girls were about 6.5 and 6.0 lbs. Both were definitely over 6 lbs and not too much difference. They were born two weeks later, Baby A at 6.11 and 5.12 lbs. So either grow slowed, which I doubt, or their weights were off by a good bit. My peri's office who did the u/s was excellent. I think it's just hard sometimes to get accurate weights at the end. They can regularly be off by a full pound plus or minus.

 

When I was 33 weeks pregnant with my girls they told me they were both 5lbs plus...they were born at 35w 6d's at 7lbs 4oz and 6lbs 4oz.

 

Trust the Machine. The Machine is Good... :Clap:

In all seriousness, the numbers provided by the U/S machine actually tell you the accuracy. This is the "+/-" number displayed after the weight. At our last appt, the twins were 3lbs and 3lbs 3ounces. The stated accuracy was +/- 7 ounces and 8 ounces. In other words, there is a range of error of about 30% at this time (31 weeks). In other words, while the U/S is much better than having no idea it is still what is called a SWAG: "Scientific Wild A.. Guess" :rotflmbo:

What I'm not sure about is what that uncertainty includes. There are 2 major factors:
(1) The error in the statistical model used to estimate the weight based on the measurements
(2) The capabilty of the operator and machine, as noted above

I suspect that the uncertainty stated only includes #1, but I really don't know.

Also note that this is a bell curve kind of thing. The stated uncertainty will emcompass some (high) percentage of results so a few will still fall outside. BUT... most will fall near the center of the range.

FWIW, my rule of thumb on U/Ses is: don't worry until the doc worries.

 

For my first preg. I had an ultrasound at 36 weeks they said he weighed 7lb7oz. I delivered 4 days later and he weighed 7lb 10oz. So for me it was pretty darn close.

 

With my LO's who were delivered at 34w0d, the u/s was right on. Well actually, off by 1 oz which I considered dang close. However, they can be off as well.

Great weights by the way!

 

I know the day before I had DS I had an u/s and they said he was over 3 lbs. When he was born the next day, he was 2 lbs 7 oz.

 

I had my identical boys 9/1/09 ... A was 5 lbs. 0 oz., B was 6 lbs. 11 oz. My last ultrasound, the previous Wednesday, estimated A at 6 lbs. 10 oz. and B at 6 lbs. 12 oz. Very close on one baby, way off on the other. It seems that we had a little TTTS working - A was actually longer than B, 19" vs. 18", but was way skinnier. My OB, too, had said the ultrasound variance would be 6-8 oz. either direction.

 

i was admitted to the hospital at 34 weeks due to IUGR with both of my girls per sono at my peri's office, and then had a sono at the hospital the following day and there was a 1 lb weight difference. when they were born 2 weeks later at 36 wks, both of them were still 1 lb UNDER the 34 week sono weights.

 

I can't remember off hand with my twins, but with my most recent baby she was weighed 5 days before being born at 8lbs 13oz. I made the decision to try for a VBAC based on that weight which was below my previous big baby. Well my labored stalled at 7cm stretchy to 9cm. They took her by c-section and she was 10lbs 11oz. Too me that was way off! I suppose it has alot to do with the technician as well.