Hi
I had a miscarriage at 9 weeks and didn't find out until I had a scan at 14 weeks. I didn't have any 'symptoms' or anything, although looking back after now having another baby, people kept telling me how ill I looked all the time, and I had a day when I felt awful for no reason at around the time the miscarriage happened, although I didn't realise why at the time. When I was pregnant with my son, I felt really healthy and people commented on how well I looked to the previous pregnancy.
Hope that helps, why do you ask?