Japanese article
http://www.nikkansports.com/general/news/f-gn-tp0-20090213-460414.htmlShe died before they got to take her to the hospital, police says it looks like it was from "natural causes." Said it was cardiac arrest. Not much other useful details.
Sex with a pregnant woman is actually not bad, and to some it's good cause you can't get her pregnant.

She most likely wouldn't have died if it was just normal sex, unless she was on drugs.
Sad news though cause that would be the loss of two lives including the unborn child. :/