‘What to Expect When You’re Expecting’? Cameron Diaz’s baby bump

The new comedy “What to Expect When You’re Expecting” promises two sure things moviegoers can expect: lots of babies and lots of pregnant women.

Babies and baby bumps were less common, however, at the movie’s black carpet premiere Monday at Grauman’s Chinese Theatre, though there were appearances from a pregnant Melissa Joan Hart, expecting her third child, and the twins who played the baby adopted by Jennifer Lopez’s character in the film.

Among the leading cast members, Lopez alone has given birth in real life, but the production gave her costars a taste of the pregnancy experience — though for some it was less than realistic.

Brooklyn Decker’s character, for example, has a stress-free, pain-free pregnancy that wins her the title “magical pregnancy unicorn” from costar Rebel Wilson’s character.

“When I put on [the prosthetic belly] they were like, ‘OK, we need it thinner, and we need it more bronze. Tan the belly. It has to look perfect,’ ” Decker recalled.

“I was like, ‘This is not fair! This is not what pregnancy looks like.’ I’m setting a horrible standard for myself.”

One thing Decker did get the hang of was “the waddle.”

“They weighted the [prosthetic] bellies,” she said. “They wanted the women to have a realistic waddle — truly, that’s what they said: ‘realistic waddle.’ ”

The filmmakers turned to Heidi Murkoff, author of the “What to Expect When You’re Expecting” advice book that inspired the movie, as a consultant on the proper size for the prosthetic bellies and breasts, including the gear for Cameron Diaz, whose fitness-guru character gets knocked up by Matthew Morrison’s character.

“When I met Cameron for the first time, she opened up her robe and she flashed me her prosthetic breasts and belly that she had just been fitted for,” Murkoff told Ministry of Gossip. “She was very, very proud of them.”

Though “What to Expect” puts pregnant women in the spotlight, its cast and crew were quick to point out that the movie something for male audiences in the form of a Chris Rock-led “dudes group,” a collection of new dads who tell it like it really is.

“[Rock’s] character is very opinionated, which is convenient because so is Chris Rock,” Amir Talai said. “I look up to Chris Rock as it is, so it was very easy to have him play my leader.”

Alex (Rodrigo Santoro) joins the group when he and his wife (Lopez) decide to adopt a child.

“They’re professionals,” Santoro said of the dudes group, which also included comedy veterans Thomas Lennon and Rob Huebel. “They were improvising like crazy. I had to keep up with them, and I couldn’t laugh.... But I was cracking up inside.”

At the premiere, the Brazilian native signed autographs for a crowd of vocal fans gathered along Hollywood Boulevard, including some who toted a large Brazilian flag.

Though the film claims the bible of American pregnancy as its namesake and inspiration, don’t expect it to be that full of advice.

“You definitely want to see this movie if you’ve had a baby recently,” Talai said. “Not because it will teach you anything at all but because it’s fun and you could use a few laughs.”

“What to Expect When You’re Expecting,” which opens Friday, also stars Elizabeth Banks, Dennis Quaid, Joe Manganiello and Anna Kendrick.

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