Sienna Miller re-enacted childbirth in Sniper

Sienna Miller thinks her facial expression in the American Sniper birth scene matches the way she looked in real life.

The actress and her fiancé Tom Sturridge are parents to two-year-old daughter Marlowe. Having experienced motherhood in real life really helped her when she had to pretend to welcome her child with Bradley Cooper's character in the true story about a US Navy SEAL.

"It was invaluable being able to remember how I felt when I first saw my daughter," she smiled to tvdigital.de.

"I think my facial expression was just like the one in the film. However, in real life I passed out straight after!"

American Sniper focuses on the story of sniper Chris Kyle and his tours of Afghanistan. It was directed by Clint Eastwood and is up for the best picture Oscar on Sunday.

"He doesn't prompt," Sienna answered when asked what Clint is like at the helm of a film. "Each scene gets done twice, at most. Clint believes that when you say a line from the script for the first time, something special happens that can't be recreated. In some ways that can be very interesting and liberating."

Sienna learnt a lot about the sacrifices soldiers make and the heartache the people left at home face.

It seems Bradley's portrayal of Chris struck a chord with many people and he's among the nominees for best actor at the Oscars.

A survey from musicMagpie found the British public is backing the actor to take home the accolade at the weekend. The recommerce site analysed 300,000 conversations from social media in order to create The People’s Oscars.

Surprisingly the UK crowd shunned Brit nominees Eddie Redmayne and Benedict Cumberbatch, putting Bradley ahead, with 31 per cent rooting for him. Birdman's Michael Keaton came in second.