I had a growth scan at 36 weeks for DS where they said he was already 4kgs, he was born 4 weeks later at 4.62kgs, so i am guessing it was fairly accurate.

At the time i chose to believe it was inaccurate + or - 10%, and tried to convince myself that he was no more than 3.6kgs. The hospital still managed to unnecessarily try to scare the cr@p out of me with this info and then to try to talk me out of a VBAC.