The 44-year-old - who shares two daughters, Rowan, 6, and Grier, 3, with husband Chris Henchy - said that she is hoping to bring another addition to her brood.
"I'd love more kids," she told Life & Style. "I don't know how much longer my clock is going to tick, so it's going to depend on my egg age."
Despite the difficulties of raising several children and maintaining her career as an actress, Shields credited her family for providing her with the support to juggle both interests.
"I don't think you ever feel you're balancing anything," she said. "My kids are great, and I have a good husband. You've just got to keep everything in the air."
Last November, Shields revealed that she contemplated suicide after suffering post-natal depression following the birth of her first child.