As Vanessa Kirby has never given birth in real life, she watched numerous documentaries and videos and shadowed midwives in a hospital in North London and even was allowed to be in a room with a woman who was giving birth.
The opening 20-minute birth scene took two days and six takes to shoot.
Despite featuring one of the longest delivery scenes ever in film, director Kornél Mundruczó stated that they still sort of cheated reality by squeezing the entire emotional roller coaster of a 10- to 12-hour delivery into a 23-minute scene.
After obtaining and reading the script, Vanessa Kirby flew to Budapest to express her admiration for the script to screenwriter Kata Wéber and director Kornél Mundruczó. She desperately wanted to play Martha because of the challenge of acting out an experience so unfamiliar to her. Mundruczó and Wéber were taken by Kirby's charisma, which reminded them of the European movie stars of old, and signed her on as Martha. They also stated that as soon as they announced it, the movie's budget was lowered because of Kirby's lack of starpower at the time.
Out of six takes that were shot for the opening birth scene, it was the fourth take that was used in the final product.