Implantation bleeding generally occurs before a missed period. It's where the little one buries itself into your uterine lining - causing slight discomfort and bleeding. Usually, it's dark blood to very light pinkish blood.
This is usually one of the signs where some women might suspect they might be pregnant, or they're not aware at all - they just assume their period is coming. :]
at 3:29 PM on Sep. 21, 2009