The "Mamma Mia!" star portrays real-life 1930s actress Marion Davies in the Herman J. Mankiewicz biopic, which chronicles his battle to complete the screenplay for Orson Welles' "Citizen Kane".
However, Seyfried admits she had nothing to fear, because the excitement of working on the David Fincher passion project, opposite Gary Oldman as Mankiewicz, made her temporarily forget she was expecting.
Recalling her initial reaction to her positive pregnancy test, Seyfried said, "I was very surprised, and I was also terrified, because the anticipation of getting to set everyday, especially when you're waking up at 3am, which is the earliest I've ever gotten up for a job, knowing that I'm gonna have morning sickness, knowing how horrible I feel physiologically, was just that was a challenge. Just getting mind over matter and getting to set (was difficult)."
"Of course, when I was on set, everything disappeared, we'd roll the cameras and I'd forget that I was pregnant for a second," she added. "But it's that challenging part at the beginning of a pregnancy that I thought was really gonna ruin my experience, but it was even better because I had this little man in me."
Filming was completed in early February 2020 and she gave birth to a son, her second child with husband Thomas Sadoski, in September.
Her performance in "Mank", which was released in November, has since won her critical acclaim, as well as a Golden Globe nomination for Best Supporting Actress.