My sonographer said you always go from the first scan.

My EDD changed from 15 July (LMP EDD - this is what I calculated myself) to 21 July (date they got from first scan). I use 21 July.

Any scans I've had after that always show various different dates whenever they measure bones etc. But they don't change it again. 21 July is it!

They still keep my LMP EDD on record though.