The 35-year-old former Playboy star declared as much in new memoir Down the Rabbit Hole: Curious Adventures and Cautionary Tales of a Former Playboy Bunny, which is scheduled for release June 23.
Madison became one of Hefner's official girlfriends at age 21 in 2001, and appeared on E! reality series The Girls Next Door during her time at the Playboy Mansion. She and Hefner, now 89, ended their relationship in 2008.
"I know how absolutely insane it sounds to want to have kids with someone in their 70s," she wrote. "You are basically robbing a child of his or her father before it is even born. Now that I'm a mom myself, the idea seems even more unpalatable."
"[Hugh learning his semen was not viable] was concrete proof slapping me in the face that there was no future for me at the mansion, and it was either sit in there and rot or take the plunge and face the world," she recalled.
Madison went on to date magician Criss Angel, All Time Low guitarist Jack Barakat and current husband Pasquale Rotella. She and Rotella welcomed their first child, daughter Rainbow, in March 2013, and married in Sept. of that year.
"I want [Rainbow] to understand why I made the choices I made," she told Us Weekly magazine of why she wrote the tell-all. "And hopefully learn from them and not make stupid mistakes herself."
Madison appeared on season 8 of ABC reality competition Dancing with the Stars and E! reality series Holly's World after leaving Playboy. She opened her own speakeasy, 1923 Bourbon and Burlesque, at the Mandalay Bay Hotel & Casino in May 2014.