Dark blood usually isn't a good sign, call your ob or go to the er! Not to startle you but when I had my miscarriage at 10 weeksnit was dark blood and clotty.
You shouod worry if it turns BRIGHT red. Brown is old blood. You're growing!
if it's dark as in brown, then it's old blood. a lot of women will go through this. I got some about the time I would've had a period had I not been pregnant. there's no cause for alarm unless it's bright red and painful. I have miscarried before, and it's a lot of bright red blood with clots and worse-than-period cramping.
If you have an obgyn call him/her.
If it is dark that is definitely not a good sign go to ER