I work as a midwife and recently a woman came in to birth at term and her scan at 38weeks (2weeks before delivery) estimated bub to be 5kilos. We were expecting a big bub and he popped out a healthy 3.4kilos. Then only a little while later another lady came in and the estimated weight was 3.5kilos only a few days before and he came out 5.7kilos (13lbs)

A lot of scans are accurate and alot are not. Agreed 4kilos isn't big. Yeah its bigger then average. Humans are getting bigger as are babies. When your birthing its not going to make much difference if bub is 5lb or 10lb.