I too had exactly the same thing at about 9wks. TOTALLY freaked me out, although I was relieved that it was never the colour of fresh blood if you know what I mean.

Turned out to be fine but worth mentioning to your GP. Mine ordered me to a week of bed rest with a med. certificate from work just to be sure; I also got to have a U/S I would otherwise had to wait another 5 or so weeks for.