Gwyneth Paltrow has revealed her marriage can be ''challenging''.

The 40-year-old actress - who has children Apple, eight, and six-year-old Moses with her rocker husband Chris Martin and recently revealed she is considering having another child - has admitted their relationship can sometimes be difficult because the Coldplay frontman is so sensitive.

Asked what is the toughest thing about being married, she told InStyle UK magazine: ''Probably our artistic temperaments together. Artists are sensitive; there are ups and downs, mood-wise. Musicians need a certain gravitas and focus in order to write. The temperament that goes with someone who is creative can be challenging.''

The 'Iron Man 3' star said that despite thinking she is ''old'' she is thinking about having one more child.

She said: ''My brain says, 'Oh, I think I'm done, the kids are big now and I don't want to go back to changing diapers'. But a part of me would love to have another. Of course, I'm old now!''

The 'Iron Man' star loves being a mother and says she relates to both her children differently, especially since she suffered from bad post-natal depression when Moses was born.