Greg, I agree with the others on this one, I wouldn't be concerned about the measurement, I measured 4cms to big from 32 weeks and my son(my second bub) he was born 7lb 12.5oz which isn't a large baby. Please do what you guys think is right don't let the midwife push you into anything you don't want to do(the scan in particular). I wish you and your wife the best of luck over the next few weeks and from the sounds of it you'll be having another wonderful birth soon!
Snoopea