The Hunger Games actress welcomed a baby boy called Felix with husband Max Handelman in March 2011. It was the couple's first child.
In an interview with Lucky, Banks admitted that she was frustrated by not being able to become pregnant, but said that she and Handelman became close to the woman who ultimately carried their child.
"It was a womb issue for me. [The] embryos wouldn't implant," Banks explained of her fertility problems.
"It's a big leap, inviting this person into your life to do this amazing, important thing for you. And it's hard losing that kind of control. But our surrogate is so extraordinary, and she's still in our lives. She like an auntie."
Banks also said that she hopes Felix maintains his sense of adventure as he gets older so that they can go skydiving together, adding: "My plan is that when Felix is 15, we'll go skydiving together. I mean, the guy is fierce and fearless, and I'm hoping he stays that way. Because I want to be that mum. The one who takes her kid skydiving."
> Elizabeth Banks: 'I miss my son when working'
Watch a trailer for The Hunger Games below: