Katherine Heigl is having trouble remembering her lines due to 'pregnancy brain'.

The 37-year-old former Grey's Anatomy star announced in June she was pregnant for the first time, and is expecting a baby boy in January (17). Katherine has two adopted daughters with husband Josh Kelley - seven-year-old Naleigh Moon and four-year-old Adalaide Marie Hope.

Despite being excited at her impending bundle of joy, she says 'pregnancy brain' is making her forget her lines while filming her new legal drama show Doubt.

"Usually I'm pretty good at memorising. I can do that pretty quickly. It's like the only thing I've got," she joked with Entertainment Tonight. "So it's really been eye-opening to me to struggle with that."

And it's not the only onset struggle the actress is having. The production crew on the upcoming CBS drama have already come up with new ways of hiding Katherine's blossoming bump, including using handy household objects in pivotal scenes.

"Today was really impressive," she shared. "I had to come up to my desk and I didn't know that they had strategically placed (a desk lamp). They were like, 'Katie, would you mind taking a small step to your right?' And I looked down and this lamp was right there. That's clever."

Katherine also opened up about her super sweet cravings while pregnant, revealing donuts are her food of choice at the moment.

"Just eat one donut a week. Just have one and then stop thinking about it," she laughed. "If I'm not on set, I don't think about them that much. And I don't eat them because they're not around. But on set, craft always has a plethora of donuts in really pretty pink boxes and I can't stop thinking about them."

And she blames her junk food cravings on her baby, adding, "It's lovely actually because I feel absolutely no responsibility for my behavior at all. It's great."

Doubt, which also stars Laverne Cox, Dule Hill, Steven Pasquale and Elliott Gould, will debut on CBS in 2017.