When it comes to Hollywood, no news is more exciting than when a celeb announces she's expecting! From guessing the gender to waiting for the first pics of the bundle of joy, we can't resist following the pregnancy.

For many of these stars, the pressure is on to get back in shape after giving birth. After hitting the gym for months -- or sometimes even weeks! -- new moms love showing off the product of their hard work. Here's a look at some of the biggest transformations and as a result, unbelievably fit post-baby bodies in Hollywood.

Kim Kardashian

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Larry Busacca/ Ethan Miller, Getty Images
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Jessica Simpson

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Alberto E. Rodriguez/ Jamie McCarthy, Getty Images
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Lily Aldridge

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Jason Merritt/ Jamie McCarthy, Getty Images
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Jenna Dewan-Tatum

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Frazer Harrison, Getty Images/ PacificCoastNews
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Kristen Bell

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Jason Merritt/ Christopher Polk, Getty Images
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Snooki

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Rob Kim/ Theo Wargo, Getty Images
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Hilary Duff

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Juan Sharma/Bruja, PacificCoastNews.com/ Paul A. Hebert, Getty Images
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Beyonce

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PacificCoastNews.com/ Larry Busacca, Getty Images
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Kendra Wilkinson

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Nate Jones/Sam Sharma/PacificCoastNews.com/ Frederick M. Brown, Getty Images
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Amber Rose

Steve Granitz, WireImage/ Frazer Harrison, Getty Images
Steve Granitz, WireImage/ Frazer Harrison, Getty Images
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Fergie

Jason LaVeris, FilmMagic/ Frederick M. Brown, Getty Images
Jason LaVeris, FilmMagic/ Frederick M. Brown, Getty Images
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Tori Spelling

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Alberto E. Rodriguez, Getty Images/ Sean O'Neill, PacificCoastNews
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Penelope Cruz

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SolarPix, PacificCoastNews.com/ Stuart C. Wilson, Getty Images
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Reese Witherspoon

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Andreas Rentz/ Toby Canham, Getty Images
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Mariah Carey

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Kevin Mazur, WireImage/ Optic Photos, PacificCoastNews.com
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Jessica Alba

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Jason Merritt/ Michael Buckner, Getty Images
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