Whilst I agree with the other two posters and what they say about scans etc, I got pregnant immediately after my miscarriage and it was a nightmare trying to get some sense of the dates etc. It also drew out my miscarriage for a further three weeks because at the first scan (an early one we paid for) I was so behind on the dates but they just said "oh it's because you had a MC so the dates are wrong" when I KNEW something was up. Had to have a further two scans on the NHS before it was confirmed as over, which only made it more stressful.
This time I am waiting for my first AF. If I can date it a lot more accurately it won't change the fate of if I lose another baby, but it will at least save a lot of stress. Whilst I knew in my heart it was over, I still had to go for my midwife appointment, booking in bloods, two scans etc. A lot of unneccesary stress that would have been saved if we'd waited for my first AF.
Just my point of view on the issue xx