"It's been very easy and so wonderful," Preston, 47, told PEOPLE at Thursday's Toronto International Film Festival premiere of her movie Casino Jack. "I've had no morning sickness and [the pregnancy] has gone by so quickly. I feel terrific."
Dressed for the red carpet in a stunning black one-sleeve, off-the-shoulder, Marchesa sheer gown with dazzling jewels, Preston – without husband John Travolta – proudly showed off her baby bump and says she's already started to count the days until her expected due date.
"John and I are completely ready. My daughter [Ella Bleu, 10] is very excited too," she says. "I can't wait for the day to come."
Another date Preston is anticipating arrives in December, when Casino Jack goes into release. Starring opposite Kevin Spacey in the drama about former lobbyist and conman Jack Abramoff, Preston is marking her fulltime return to acting since the January 2009 loss of her 16-year-old son Jett.
"I'm thrilled to have been in this film, and I loved every minute of it," says Preston. "I love this film because I hadn't been in a movie in over a year, so it was nice to be back."