Tahlia said, "I'm three months along, so we've just hit that 13-week mark."
The model continued: "I'm showing a little bit, but I don't know if it's just all the food I've been gobbling up or if it's a Burgess baby, they are quite large kids."
The couple told The Daily Telegraph that they won't be keeping the baby's gender a surprise.
"I want to keep it (the gender) as a surprise," the Miss Universe Australia finalist said, "But Tom has been begging me every single day, so I think just to shut him up I'm going to find out for him and do something nice to celebrate that."
The pregnancy hasn't been smooth sailing for the first time mum, with Tahlia revealing that she was diagnosed with hyperemesis gravidarum and bedridden for most of the first trimester.