Katherine Heigl is craving donuts during her pregnancy.

Katherine Heigl

Katherine Heigl

The 'Knocked Up' star is expecting a baby boy with her husband Josh Kelley, who she wed in 2007, and revealed she's developed a sweet tooth and always feels "really hungry".

She said: "I wake up every morning really wanting a donut... or 10. Thankfully I don't really have many symptoms. I'm just really hungry."

The 37-year-old beauty - who also has adopted daughters Adalaide, four, and Naleigh, seven - has revealed the siblings are "excited" for the arrival of their brother and can't stop asking her if he's been born yet.

She told 'Entertainment Tonight': "They're so excited.

"For them, it's an 'out of sight, out of mind' thing. They'll forget about it for a while, and then suddenly be like, 'Hey have you had that baby yet?' "

Katherine announced she was expecting in June and the family plan to visit Utah for Christmas, very near to her due date of January 2017.

There they will be joined by country singer Josh's brothers and their children and they've already got ideas for the unborn tot to play with Josh's brother's little boy Ward and the two girls.

Katherine said: "Josh is hugely ready [to have a boy].

"He's just surrounded by women! It's me, the two girls, my niece Madison often lives with us in Utah... and then my mom.

"His brother had a baby last February, a little boy named Ward. "They're already talking about their foursome."

The 'Doubt' actress recently admitted motherhood has changed her perspective on life.

She said: "It's been a huge blessing - it gave me perspective. Before them, it was all about my goals as an actor. They helped me to take a step back and go, OK, I have some important work to do on this earth.

"Naleigh is going on 13! She's very sassy and confident.

Adalaide's a total tomboy who's obsessed with bugs. The other day she was digging for worms."