Radio and TV host Chrissie Swan says she has struggled to quit smoking since discovering she is pregnant with her third child.

The Mix FM presenter - a former Big Brother contestant - made the confession to her Melbourne radio audience this morning.

Swan said that finding out six months ago that she was pregnant again was a "massive surprise" and she had since attempted to give up cigarettes.

"I tried to go cold turkey like I did with (son) Leo and I was confident that I could do it, but I couldn't do it," an emotional Swan said.

"I just failed and failed, time after time. I'd win for a few days then I would have one."

The Can of Worms TV show presenter said she quit smoking for "a couple of years", but started again about a year ago.

Though she blamed a heavy workload and new home among stress factors in her life, she said: "These [are] not excuses, there is no excuse for smoking.

"Obviously I know it's wrong, I'm not an idiot.

"No smoker wants to smoke, especially when they're pregnant, but it is clearly an addiction and a very serious one."