Finnish director Hanna Bergholm knew from very early on she wanted her horror film Nightborn to tell a story about difficult emotions that arise when you become a parent and to break taboos that still exist around motherhood.

"I knew that I wanted to tell a story about difficult emotions that appear when you are a parent, mother, or a father, and how to face your emotions and yourself," she said at the Berlin Film Festival, where the film -- original title Yön Lapsi -- is featured as part of the Competition section.

This Nordic tale of mythological influences follows Saga (Seidi Haarla) and her British husband, Jon, played by Harry Potter star Rupert Grint, as they retreat to the seclusion of Finland's forests and excitedly embark on their new journey as parents.

Once the baby is born, however, their joy fades quickly as his appearance and behaviour raise suspicions in Saga that something is terribly wrong.

"It was very important that it feels like everything comes from real emotions of these characters," Bergholm said. Saga is the central character and the film tells things from her perspective.

It is then up to the audience to decide how much of what is happening is real or not, she said.

Grint said the film, which came after he had just found out he'd be having a baby, resonated with him."(Being a parent) is such a scary experience."

Bergholm also wanted to show the kind of physicality which is often left out of conversations.

"I wanted to show the birth of people and the blood in that," she said.

"And you know, these everyday life things, we all got it and a female body can break in childbirth in various ways and it's something we never talk about (...) And it's just human, it's natural."

When asked about whether she took inspiration from Roman Polanski's "Rosemary's Baby," Bergholm answered: "when we wrote this with Ilja (Rautsi) we kind of joked that this film starts where Rosemary's Baby ends."

-Reporting by Linda Pasquini; Editing by Sharon Singleton/Reuters