Surrounded by her boyfriend, Derek Thomas, her mom, Demi Moore, and her sisters -- Tallulah and Scout Willis -- Rumer explained that everything was going according to the birthing plan, but labor came on hard and fast, and she "dilated from two to eight inches in about an hour."
This meant she quickly had to move into a bathtub to begin pushing, but her doula realized that her water was still intact.
"She was checking me and felt my water bag bulging, but still not popping, which was wild," Rumer recalled. "So, I was like, 'Well, should we break it?' She goes, 'Well, you can.' I'm like, 'What?!' I was like, 'Are you serious?'"
Serious indeed, Rumer decided to take matters into her own hands. "I reached my finger up there, and I'm feeling and it was crazy," she shared. "I could totally feel this little bag -- it feels like a water balloon, but with a bit tougher skin."
"[The doula] said, 'OK, on the next contraction, just push against it with your finger.' And I popped it," Rumer continued. "I think there's a photo of me and I just have this look of shock and surprise on my face."
From that point on, the rest of the process apparently happened swiftly and was over before she had time to really realize everything that was happening.
"It was like, I pushed a little bit... well, I didn't push a little bit, I pushed harder than I've ever probably, but it was literally like I pushed, her head was out. I pushed again and her whole body was out," Rumer said.
"There was no pause in between," she added. "It wasn't one of those moments where it was, 'Oh, your head is out.'"
She recalled how, when her baby girl came out, her doula and her partner were there to catch her. The newborn was wrapped up in the umbilical cord and there were "four hands under there" working to unwrap her.
As soon as she was untangled, Rumer said her little girl was "was in my arms," and she described the experience as "the most ecstatic, joyful moment of my entire life."
In May, Rumer commemorated her first Mother's Day with a series of intimate portraits from her childbirth journey. The images show Rumer's mom by her side throughout the process.
"To be able to celebrate this day with you is beyond words, the privilege to walk in this path of motherhood with you by my side to support and guide me is something I have only dreamed of," Rumer wrote in a tribute to her mom. "Thank you for holding the most beautiful space for me as I made the transition from maiden to mother. Thank you for helping me walk through and rise to the occasion to have the birth I dreamed of."