I would be really concerned if my partner bled during fisting, especially if it was not near her period. What do you mean by 'a lot' Redpepper? Coating your hand, gushing out, dribbles?
I have not had that happen and am stumped as well. If it was a significant amount of blood, I do not see how a scrape or a nick alone would produce that. Maybe the IUD opened up the cervix enough to have blood leave the uterus early?