following on from my other thread, an update for anyone who's interested:
I finally talked to the sonographer this morning, and she explained to me that I wasn't going to be rescanned because of the femur length - as that was "only" one week behind expected dates and the result of my blood test was normal, they weren't worrying about that one.
The reason they are rescanning is because of the ventricles in the brain - the measurements for those were the upper side of normal - 9 and 10 mm when the upper limit of normal is 10 mm. They are going to check at the next scan how their size will have developed. If they are too large that can be a sign of hydrocephalus, apparently. So that would be very worrying, but I'm holding on to the fact that the measurements were normal, just large normal.
So I do feel calmer now, and am taking the view that I will wait and see what happens next week.
Thank you for all messages of support! They really helped a lot!!!!