"I was terrified. I got pregnant when I was 22 years old, and I didn't know how to balance work and motherhood. You just do it," began Witherspoon, 44, who welcomed daughter, Ava Phillippe, in 1999.
"I didn't know if I was going to have steady work too, I wasn't a popular [actress]," she continued. "I made movies but I hadn't established myself as someone who could demand that it shoot close to my kids' school. [I] didn't have any real power or leverage within my industry."
"I think I was just like every other mom trying to figure it out," Witherspoon added. "There's a lot of, first of all, compromise. You take the food out of your mouth, the clothes off your back, the sleep out of your life, but every bit of that sacrifice is truly worth it. That's what makes me wake up on a Sunday. It's not movies or my job, it's my kids."
Witherspoon shares daughter Ava, now 21, and son Deacon, 16, with ex-husband Ryan Phillippe. The "Little Fires Everywhere" star and the actor, 46, were married for nearly eight years, before splitting in 2006. Witherspoon went on to marry Jim Toth, a talent agent, in 2011. The couple have a 7-year-old son, Tennessee.
The "Legally Blonde" star has previously recalled the struggles she faced while trying to balance her career and motherhood at 23.
"I've been a mom since 1999. I got pregnant [with Ava] when I was 22 and delivered when I was 23," she said on her Reese Witherspoon x Hello Sunshine YouTube channel last September. "To be totally honest, it was scary. I was scared. I didn't know what it was going to do to my job or my career. Your entire life will change -- everything you believe, every piece of food you eat, every piece of independence you have. You can't go out without thinking of another person."
Though she was "scared" at the time, Witherspoon said she's "glad" she became a mother at a young age.
"I find that having little kids is more physical and it's just really hard on your body," she explained. "I had one at 23, one at 27 and then again at 37. And oh, my God, having a baby at 37 was so much harder. This is just me being real."