Katherine Heigl's "basketball" sized baby bump is making it tricky for her to shoot sex scenes for her new TV show 'Doubt'.

Katherine Heigl

Katherine Heigl

The 38-year-old actress is expecting a baby with her husband Josh Kelley but for her role as defence attorney Sadie Ellis she has to get steamy with her co-star Steven Pasquale, who plays a client who her character falls for.

Now, with Katherine in her third trimester, her swollen stomach is getting in the way of their fictional lovemaking for the programme which will air from February on CBS.

Speaking to 'Extra', she spilled: "There's just this basketball between us. I'm like, 'I'm so sorry, so awkward!' and he was lovely, but you don't feel beautiful, really. It can get a little steamy, but with this situation it can't get that steamy."

Katherine - who is already a mother of two adopted children, daughters Naleigh, seven, and Adelaide, four - has enjoyed every aspect of her pregnancy, although she has been shocked by how big her butt has got.

She said: "I feel great. It's been a really easy pregnancy and I had no idea what to expect ... It's been kind of great. Everything's just expanding. I don't understand why it has to go both ways. What does my butt have to do with any of this?"

Katherine's daughters Naleigh and Adelaide are getting very excited to meet their new sibling

She said: "I think they forget. It's a little like out of sight, out of mind, but then suddenly it will be like, 'Hey, have you had your baby yet?' I love that they always say it's the family's baby. We're throwing a newborn into the mix and starting all over. We're thrilled and excited."