Kate Winslet, Molly Sims and Other Celebs Paint Their Baby Bumps for The Belly Art Project

Spanx founder Sara Blakely came up with the idea for The Belly Art Project — a photo book featuring pregnant bellies made into works of art — when she was pregnant with her first son.

“I woke up in the middle of the night with an incredible urge to turn my big belly into a canvas, and I wanted to capture the moment in a fun and playful way,” Blakely, 45, tells PEOPLE. “The Belly Art Project was born, and has been a true labor of love for the past seven years.”

Over the years the project has featured more than 100 women’s bellies, including those of some of Blakey’s famous friends: Molly Sims, Kate Winslet, Savannah Guthrie, Alyssa Milano and Coco Rocha are just some of the celebs featured in the one-of-a-kind photo collection.

Kate Winslet/ Courtesy The Belly Art Project

Savannah Guthrie/ Courtesy The Belly Art Project

Alyssa Milano/Courtesy The Belly Art Project

“Kate Winslet was the first one to say she wanted to be in the book — that was a moment where I thought, ‘Oh my God, someone this amazing and well respected for being one of the best actors of our time wants to do it!'” says Blakely.

But she didn’t just ask her friends to participate. Blakely also approached strangers in airports, nail salons and weddings to be a part of her project.

“I would approach these people and say, ‘I promise I’m not crazy! It’s just a really great, creative way to capture this time in your pregnancy,'” she says. “I would say 95 percent of the women that I approached […] were like, ‘Oh count me in this is amazing!'”

Blakely says it was easy for her to get the women on board because the book’s proceeds benefit Christy Turlington Burns’ Every Mother Counts, a non-profit organization dedicated to making pregnancy and childbirth safe for every mother.

“Other moms-to-be were happy to belly up to the cause in support of maternal health,” says Blakely.

WATCH: Did You See Adam Levine’s Hilarious Belly Bump?

As for the creative designs on each belly, Blakely says they were a mix of ideas she had in advance and spur-of-the-moment inspiration.

“Most of the belly art concepts came to me during my best thinking time – on my commute to work or at stoplights,” she says. “Other ideas were a collaboration that evolved once the paint met the bellies.”

She hopes people will enjoy the book, as well as the purpose behind it.

“Moms supporting moms is a wonderful thing,” she says, “and it makes for amazing, fun pictures!”