Estimated fetal weight on scans - how accurate?

[Solero]

Am 31+5 with #2 and had a growth scan today as am type 1 diabetic and baby's estimated weight was already 6.2lbs. My diabetes has been well controlled for most of the pregnancy (last HbA1c was 6.8) but sugars are starting to climb quickly now. I am a little worried that she is already quite large altho midwife says bump is normal sized and the sonographer didn't seem overly concerned. So how accurate are these measurements?

My midwife sent me for a sizing scan because i was a big as a house - i was told "no bigger than 7 pound" ummmmm yeah ok - NINE pounds nine!!!! FFS

Ds would be at least 10lb he was 7.12

Best friend was told baby has possible serious problems as she was no more than 4lb and has a very tiny head. 6 days later she was 8lb with a perfectly normal head.

So it seems its def not an exact science The only thing the sonographer did say was that she had quite a big tummy but am sure my first DD was the same and she was dinky when she came out. I guess I will have to wait and see what they say at my appt on tuesday.

My scan has a +/- 25% thing on it -baby allegedly 5 lb 1 at 32 weeks - dreading huge baby

Like many others, it was wrong for me! Growth scan at 33 weeks (due to reduced movement, thankfully all was well) - they told me baby would be 9lbs+. Bump measured at the top of my chart. They told me I was having a big baby! He was born at 40+3 weighing 6lbs11!