How accurate are ultrasound tech when measuring baby's weight?

They are not very accurate, i had scans every 4 weeks to check his growth and was told he would be at least 10lbs, i had him 8 days late weighing 8lbs.

Its mostly like a pound up. Or down the baby gains the most weight the last few weeks Good luck & congratulations

At this point, in the 2nd trimester, they're relatively accurate. However, in the 3rd trimester, they're notoriously unreliable for sizing! They won't tell you that, but they tend to be off (toward the end) by as much as 25%! Docs frequently use ultrasound and the spectre of a "big" baby to scare women into inducing unnecessarily, even early!

The nearer to term, the less accurate. I went over with all my babies and had ultrasounds at 41 weeks to monitor fluid etc. all 3 times they said between 3 and 3.5 kg and my first was 4.8kg, my second 4.2 kg and my third 4.5 kg. Maybe they didn't want to scare me:-)-lol! But I think at that point they're done developing and pretty much just gaining weight.

Very inaccurate with both of mine - like 30% out.

I had to have a scan at 36 weeks due to measuring small. Well my baba wasn't small lol, at that scan he was 7lb 9oz and born at 41+2 weeks and was 8lb 8oz

Well, the farther along you are, the less accurate it will be. My son weighed 6lbs 2oz according to an ultrasound 3 days before he was born - at 7lbs 14oz!

for ultrasounds closer to the end I would give it plus/minus 1 pound. I don't know anybody that was given an accurate weight as to how big or small the baby would be once born.