The Insider.com

Jennifer Lopez stars in the ensemble comedy What to Expect When You're Expecting, based on the bestselling "bible of American pregnancy," and in an Insider exclusive she says that the movie is just the opposite of the popular book: "You just never know what to expect," she says. "You really, really don't."

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"I had just had my own babies; I was very familiar with the book and I thought [of the movie], 'Oh, they're going to take people through what a pregnancy is, very by-the-book,'" says J.Lo. "But they kind of flipped that on its head and said, 'No, it's not about what you expect at all, like in the book. It's the opposite of that.' You never know what you're going to get. You never know what it's going to be, and all of that is part of the miracle, of the magic of it, and that's what I like about it, because it's true. It's so life-changing and it's just not what you'd ever expect."

Inspired by the well-known New York Times bestselling pregnancy manual, What to Expect When You're Expecting chronicles the hilarious and heartwarming stories of five couples who face the many challenges adjusting to pregnancy and parenthood. Elizabeth Banks, Cameron Diaz, Chris Rock, Chace Crawford, Brooklyn Decker, Anna Kendrick, Matthew Morrison, Dennis Quaid, Rodrigo Santoro, Ben Falcone and Joe Manganiello round out the cast.

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What to Expect When You're Expecting opens in theaters everywhere on May 18, 2012 -- just in time for Mother's Day.