Hi Cindy, I'm so sorry you have this worry hanging over you now, it must be awful. I'm pretty sure I've had ultrasounds that showed measurements about a week behind, but I think these were at 10 and 12 weeks (in two different pregnancies - one successful, and my current pregnancy which is now at 14 weeks). In my case the scans simply resulted in my being given new delivery dates and there was no suggestion of any problem. It's entirely possible that you O'd a week later than you thought, so maybe your ob has some other reason for suggesting you prepare for a miscarriage? Why don't you give him/her a call for some clarification. Best of luck to you.