LONDON • Vanessa Kirby has never given birth, but after shooting her first lead movie role in Pieces Of A Woman, she kind of feels like she has. "Whenever I see a pregnant woman now or someone's telling me she has just given birth, I smile," she said in a recent video chat. "I feel with them."

The two full days she spent shooting a searing scene for the film could explain this psychic confusion, as could the thorough way Kirby, 32, immersed herself in the role.

In Pieces Of A Woman, which debuts tomorrow on Netflix, Kirby plays Martha, a pregnant woman whose home birth goes horribly wrong. This pivotal event at the beginning of the film plays out in a 24-minute, single-take scene that starts with Martha's first contractions and ends in tragedy.

The camera follows Martha, her partner Sean (Shia LaBeouf) and a midwife, Eva (Molly Parker), around the couple's apartment, condensing the agonies of labour into under half an hour.

Last September, the film premiered at the Venice Film Festival, where Kirby won the Best Actress award and began to be talked about as an Oscar contender.

She talked to women who had given birth and women who had had miscarriages, as well as midwives and obstetrician-gynaecologists at a London hospital. While she was there, a woman arrived having contractions and agreed to let the actress observe the birth.

The experience of watching that six-hour labour "changed me so profoundly", Kirby said.

"Every second of what was happening to her, I just absorbed."

And she began to understand how to play Martha. The woman in the hospital went into a primal, animal-like state, Kirby said. "Her body was taking over and doing it, so that helped me so much for the scene," she added.

Over two days, that long take was shot six times. In a telephone interview, the director, Kornel Mundruczo, who also works in theatre and opera, said that preparing it was like getting a stunt scene ready: "Lots of planning, but you don't know what's going to happen."

Inspired by the labour she had observed, Kirby tried to think as little as possible, she said, and not judge what her body was doing in the scene. After a decade of work, Pieces Of A Woman is her first time leading a feature film and it is a bold and memorable role that shows her flexing her acting muscles.

After graduating from college, where she studied English literature, Kirby was accepted to the London Academy of Music and Dramatic Art in 2009. A few months before term began, though, she was offered three stage roles by David Thacker, a former director-in-residence at the Royal Shakespeare Company, who was then the artistic director of the Octagon Theatre in Bolton, a town in northern England.

Kirby describes that season as her training. "I learnt everything there," she said. Working with Thacker taught her to trust herself, to find her way as an actor, rather than waiting for other people to tell her what to do, she said.

Kirby has been working steadily ever since, with lead roles in the West End, as well as high-profile supporting roles in films and British television costume dramas.

She starred as Princess Margaret in the first two seasons of The Crown, a performance that earned her a British Academy of Film and Television Arts award. In 2018's Mission: Impossible - Fallout, she played the White Widow, a glamorous black-market broker who carries a knife in her garter and knows how to use it.

It is fitting, given Kirby's theatrical background, that Pieces Of A Woman started life as a play, written by Kata Weber, Mundruczo's partner, who drew on the couple's own experience of losing a child.

Mundruczo, 45, said he hopes watching Martha's experiences will encourage "people to be brave enough to have their own answer for any loss".

In recent months, model Chrissy Teigen and Meghan Markle, the Duchess of Sussex, have shared their experiences with pregnancy loss.

Kirby said that, while researching for the role before filming, she found that women who had experienced one were "really relieved to talk about it" and appreciated that someone wanted to understand.

Her next project will see her co-starring as Tallie, one of two farmers' wives who fall in love in the United States in the 19th century in The World To Come, a meditative drama from Norwegian film-maker Mona Fastvold.

And after that?

Kirby said she was reading scripts, on the hunt for the next role that will scare her.

She is looking for an "untold story about women", she said, that will feel as urgent to tell as Martha and Tallie's did.

"What's that expression?" she said. "Feel the fear and do it anyway."

NYTIMES