They proudly bare their bellies for relentless paparazzi and red carpet events. In interviews, they gush about how they can eat all the junk food their strict diets wouldn't normally allow.
But with many Hollywood moms, once their baby bump turns into a baby, they're back to looking svelte and skinny faster than you can say "post-natal Pilates."
Reese Witherspoon slimmed down within two months of giving birth to her son in 2003. Kate Hudson gained 60 pounds while she was pregnant with son Ryder (much of it thanks to Haagen-Dazs Swiss Vanilla Almond ice cream, she told the New York Post) and dropped it all in a matter of weeks so she could film "The Skeleton Key."
Reality TV star Trista Stutter graces the latest cover of Us Weekly, toned muscles bared, baby boy held high, beaming about how sexy she feels now that she's finally shed the 30 pounds she put on during pregnancy.
Why do Hollywood moms insist on turning their swollen bellies into six-pack abs so fast?
"These people are getting photographed in their public and private lives. They want to look their best," said Dina Sansing, Us Weekly's West Coast deputy editor. "They're not taking a year off to hang out with their kids. They're going back to work as soon as possible."
But from a health perspective, hopping from the delivery room to the Hollywood rat race -- as Gwen Stefani, Katie Holmes and Keri Russell did -- can be damaging.
"People want to be out on the red carpet two days after they give birth. That's insane," said Keith-Thomas Ayoob, a dietitian at the Albert Einstein College of Medicine. "If you go to extreme diet measures, that's always a concern."
Some of the diets that are so hot right now among A-Listers can be downright damaging for new moms. According to Ayoob, vegan and raw-food regimens are no-nos, especially for women who are breast-feeding. Same goes for crash diets and vigorous exercise/minimal eating while pregnant to stave off extra pounds.
"I do worry about very thin, slender models when they get pregnant," he said. "It looks like they're going to give birth to a jellybean or something."
Beyond that, provided they're under the guidance of health and fitness professionals, doctors said there's nothing wrong with shedding 20 to 30 pregnancy pounds within two months. But nonfamous new moms, keep in mind that Halle, Heidi and all the rest have superpowers mere mortals do not.
"Most top celebrities, in addition to their doctors, have child care help, household help, trainers, nutritionists, cooks and chefs -- or at least they have Jenny Craig," said Dr. Donnica Moore, president of New Jersey's Sapphire Women's Health Group. "So it's not like they're running themselves ragged."
Of course, not all celebrity moms jump in the express lane to get back their pre-baby figure, and that can sometimes be a boon. Former Playboy playmate Jenny McCarthy became the face of Weight Watchers after admitting she used the program to shed the 80 pounds she gained during pregnancy.
But the fast route -- jogging with junior down Melrose Avenue and opting for Pinkberry over Haagen-Dazs -- seems to be the one the majority of new Hollywood moms take. Which is fine, as long as they don't attempt to slither into a size zero Marchesa gown five days after giving birth.
"Childhood changes your figure. There's no getting around that," Ayoob said. "When you start to mess around with Mother Nature, you can have some very bad results."