How accurate are U/S Weights?

Hi everyone, hope all is well!
I'm just curious as to how accurate the weights are, during an ultrasound? So far, my babies have been within one ounce of each other the entire time and since I'm getting closer to delivery, I wanted to know if I should really believe that if they were to be delivered at that point, would they really weight that? What brought this to my attention was the recent births of Nancy Grace's twins....their weight difference was significant..I'm wondering if she had prior knowledge that they would be so different?

 

With my first son they gave me a u/s in labor and told me 7.5 lbs. He was 9.5 lbs when I gave birth the next day.

I think they were more accurate with the girls (who were born 4 oz different in weight), but had also estimated them to be smaller than they really were. I can't remember it as well, even though it was much more recent. That year of sleep deprivation...

 

Not very accurate at all from what I hear! The tech told me it's based on a forumla where they put in the measurements of the head, the abdomen, and the femur bones -- but if one tech measures a little differently from another, you'd get different results each time. I know someone who was told her baby was 5+ lbs. in August and that she would have a 9+ lber when she was due in October. She wound up having the baby two weeks early ... and he weighed less than 6 lbs! So they were WAY off with their estimate! It's fun hearing a number at an u/s, but I don't put too much faith in it!

 

I've heard they will often vary a pound in either direction. During my ultrasounds they never told me how much the approx. weight was so I was shocked when my two came out in the seven pound range! (7.7 & 7.11)

 

Very accurate in my case. They were estimated 2lbs4oz and 2lbs5oz at 26 weeks, 4lbs5oz and 4lbs6oz at 30 weeks, lower 6lbs range at 34 weeks and they were born 7lbs11oz and 7lbs10oz at 38w2d. They always measured very close together (1 oz), were born 1 oz apart and measured ahead consistently, this was also correct. They were born 12 days early, and basically grew at the same rate my oldest did, who was born "3 weeks later" (41w2d) and weighed 9lbs2oz.

I agree they're often wrong when they expect large babies (especially twins), but I think it also depends on the tech - some are simply better than others - and the machine they're using.

 

I was told my DD was 5-11 three weeks before she was born weighing 5-2.

I was told my DS was 6-2 three weeks before he was born weighing 6-6.

 

At 37 weeks I was told:

Baby A was 6.8lbs....he was actually 7.10lbs...1lb and a couple ozs difference

Baby B was 5.7lbs....she was 5.3lbs...4ozs difference

They were born a week later at 38 weeks.

So one baby pretty much right on and the second baby they were off by a lb.

 

I had my last u/s on a Thursday and the girls were born on Sunday. There was only a couple oz weight difference between their estimated weight and their birth weight. We had weekly u/s done by the same doctor from 19 weeks on though so they were very well measured.

Dax was measured at 8 lbs one week before his birth. The two techs said that the u/s usually measures high at that point so he's more likely around 7.5 lbs. He actually ended up being 9 lb 9 oz.

Ultrasounds can be really off late in pregnancy because the babies are getting so big and filling up the space in the uterus.

 

2 days before delivery Katie was estimated at 3lbs 9oz and Carli at 3lbs 8oz. Katie was born at 3lbs 14.5oz and Carli at 3lbs 9.5oz, so they were fairly accurate with mine.

 

My U/S tech always tell me + or - 10 oz

 

At my ultrasounds, the babies were always within a couple of ounces. At the last one:

Baby A was 6 lbs. 12 oz.
Baby B was 6 lbs. 5 oz.

Six days later, the babies were born:

Baby A was 5 lbs. 10 oz.
Baby B was 6 lbs. 12 oz.

Apparantly the ultrasound tech labeled A based on who was on the right side instead of who would come out first like the doctors do.