Until now, it was easy to dismiss the Twilight film series — which has grossed nearly $2 billion worldwide — as fodder for adolescent girls. Lots and lots of girls.

But with the arrival of The Twilight Saga: Breaking Dawn - Part 1, which will begin breaking box office records at 12:01 a.m. Friday, the story takes a surprisingly adult turn. This one tackles marriage, sex, abortion and family demands, themes that can no longer be deemed kid stuff — and reflects the growing inclusion of adult content in TV shows and movies aimed primarily at teens.

The legions of fans who devoured Stephenie Meyer’s novels, which have sold more than 100 million copies, knew what was coming: In Breaking Dawn, the 18 year-old Bella (Kristen Stewart) marries the vampire Edward (Robert Pattinson), who looks 17 but was born in 1901 (he could be her great-grandfather!) They honeymoon on a remote island off the coast of Brazil, where Bella loses her virginity and discovers vampires like their sex extra rough.

Then, along with the black and purple bruises dotting her body, Bella discovers she is pregnant — and the baby she’s carrying, which is growing at a supernaturally fast rate, may be an immortal human-vampire hybrid that will drain the life from her before it’s born. Edward and his clan of vampires implore her to terminate the pregnancy, because it may kill her. But Bella refuses.

Strong stuff — strong enough, in fact, to earn the first cut of Breaking Dawn - Part 1 an R rating. But Oscar-winning director Bill Condon ( Dreamgirls, Kinsey, Gods and Monsters), who shot the two Breaking Dawn movies back to back, knew he was required to edit the film down to a PG-13.

“More than anything, I wanted to make sure that the intensity of two specific things — the first time they make love during their honeymoon and the birth scene — wasn’t watered down,” Condon said from Los Angeles. “The ratings board is so subjective. They have certain rules everyone has to follow, and one of them has to do with the amount of thrusting you can show. There was never any nudity or anything like that. And the solution we settled on was to give you Bella’s point of view as much as I could in those scenes. For example, during the birth scene, we limited what you can see to her point of view as she’s lying on that gurney. And it turns out that allowing the audience to use their imaginations to fill in what’s happening makes the scene even more powerful.”

Despite the restraint, though, Breaking Dawn - Part 1 represents a surprisingly bold change of direction for a series that, in the previous three films, had traded primarily on high-school angst and boyfriend troubles. This time, there will be blood. The movie is the latest example of an ongoing cultural shift that allows movies ( Easy A, Remember Me) and TV shows ( The Vampire Diaries, Gossip Girl) aimed at teenagers to tackle subject matter that might have seemed too adult even a decade ago.

“The culture has gotten more comfortable over time talking about issues,” said Breaking Dawn screenwriter Melissa Rosenberg, who was an executive producer on several TV series (including The O.C. and Dexter) before signing on to adapt all of Meyer’s Twilight novels into movies. “Maybe this is an overly hopeful and idealist perspective, but we’ve learned that talking about something is much healthier than pretending it doesn’t exist. In the TV and film world, that allows us to get into these issues within the context of a story. Everyone is always nostalgic about the 1950s, but there was all this horrible stuff going on then, too. Film and TV have helped bring these things out into the open.”