Stephenie Meyer does correspondences on Twilight Lexicon and i remember reading it somewhere so here it is!
"Several girls wanted to know if Edward would have a more difficult time being around Bella when she’s having her period. Answer: Yes, a little bit, but he would never say anything about it–much too much of a gentleman. And Bella would be way to embarrassed to ask. (It’s not the same as a cut, though. It’s sort of "dead" blood, if you get my meaning)."
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