Ellen Pompeo has opened up about her work on the eighth season of Grey's Anatomy.

In a set visit to the long-running show, the 42-year-old actress spoke to E! about the challenges of motherhood, both on the show and in her own life.

Pompeo, who gave birth to a baby girl - Stella Luna - in 2009 with husband Chris Ivery, said: "It is challenging. I have my days where I feel really guilty that I've been here every day if I have to work a lot.

"But... I am so lucky to live in a country where a girl like me can make this kind of living, achieve her dreams and reach her goals. And I don't think anywhere else in the world can girls have the freedom that we do here to have these amazing careers and be mothers."

Pompeo's character Meredith is also a mother on the show, to baby Zola played by twin girls. "Those babies are amazing," she added. "They seem to know when the camera is on them.

"When we were trying to get her to walk, and they're really on the verge of walking, and just when the camera was on her, she just stood up and walked across the room! It was really a real moment and so it really has been fun."

Pompeo has been a lead on the medical drama since 2005, but may not be returning for another season.

It was recently announced that there will be a Grey's Anatomy and Private Practice cross-over, but when asked about it, Pompeo said: "I don't know because I'm not in it!"

Grey's Anatomy airs Thursday nights on ABC.

Watch Ellen Pompeo in the Grey's Anatomy set visit below:

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Ellen Pompeo on juggling Grey's Anatomy, parenting: "It's challenging"