My SIL's mother had full blown bleeding for the first six months of her pregnancy with my SIL. She didnt know she was pregnatn because she had it just like her regular periods. She coudlnt understand why she had been gaining weight(she didnt gain much about 10 pounds by then) and that she had been feeling sick off and on during that time. She had gonet o see her doctor and he did a test just to rule it out. Come to find out it runs in her family.
A friend of mine, had normal periods every month, her tummy was hurting very bad and she went to the hospital turns out she was in labor, the doctors were confused because she didn't even have much of a tummy that was showing, it just looked like she gained a few pounds, I think she only gained about 11 lbs