The TV star was expecting her second child Valentino Luca when she hosted one series of the ITV1 daytime show with Des O'Connor in 2004.
"Most of the time we were [having fun] but when you do a daily show you can't have an amazing time every day - your job is to be the best you can be," Sykes told Take 5 magazine.
"You can't go on screen being miserable, although when I was pregnant I had a few hormonal days and I think that was clear for everyone to see.
"A show like that is fun but it's hard work too. You have to research every guest to make it look seamless."
In October last year, Sykes admitted that she once snubbed an offer to play a Bond girl.