how long into a pregnancy do lines stay faint for on a home pregnancy test?

[flower]

ok so i wasn't due on until this thursday asuming i was having a 28 day cycle (i had a miscarriage 3 months ago) however i knew id ovulated on CD10 as i got pains. so i did a test on friday afternoon and there was a very faint line there. i then did a clearblue digital and that said 'pregnant'.
today i went to the docs because i wanted it on record that i was pregnant (this being due to the doctors attitude at the hospital when i had my miscarriage) anyway he did a test and after a minute or so a very faint line came up. hes booked me in to see him in another week and said the line should be alot darker by then but it is definately a faint positive.
but im worrying a little that the line should have got a bit darker by now.
what do you all think?

 

[tickle me fickle]

Don't look for lines, look for a blood test.

 

[Due 8th Jan 2010]

I wouldn't worry about it a line is a line. I had the opposite my lines where dark to start with and then got lighter I swore I was having a m/c. But everything turned out fine.