Sienna Miller has said she will not be pressuring herself to have the perfect birth with her second child – which she revealed is another daughter.

The actress, 41, is expecting a child with 27-year-old The Crown actor Oli Green, following the birth of Marlowe with The Sandman star Tom Sturridge in 2012.

Miller said she will be doing this labour differently, now she is “aware of what that’s like”.

“I spent so much time preparing for the birth, and absolutely no thought was given to what happens when I’d get home with a baby,” she told Vogue magazine of her experience with Marlowe.

Despite wanting a natural birth, Miller was induced in hospital and had an emergency C-section after a 27-hour labour.

“It was like a horrible trick of the universe,” she said.

“It was so essential in my mind that I got it ‘right’, and so emblematic of the kind of mother I would be that I didn’t.

“But I know in retrospect that was just the demons of new motherhood. (This time) I just don’t think I’ll put that pressure on myself.”

Miller said she still wants to try for a natural birth with baby number two and has recently switched to a doctor who is aligned with that.

The actress, who will next be seen in Kevin Costner’s film Horizon which she filmed in Utah while suffering from morning sickness, spoke about the 14-year age gap between her and partner Green.

“I don’t think you can legislate on matters of the heart. I certainly have never been able to,” she said.

“For Oli, it is real that I might want to be with someone older.”

Miller said there is an “awareness of the dynamics that enter relationships between men and women now that we just didn’t have 20 or 25 years ago”.

She continued: “I feel like my whole adolescence was dodging bullets and advances in a really delicate way, to not offend somebody.

“Whereas the girls that he grew up with, they’re probably like, No – no, thank you. Moving on.”

The couple met at a Halloween party thrown by a mutual friend and have since moved to London together.