"So happy about our little girl! Thank you all for the happy wishes," the 28-year-old yoga teacher tweeted.
Thomas, who is due to give birth later this summer, jokingly added on TV show Extra that with two female dogs and a baby girl in the house, not to mention Baldwin's teen daughter from his previous marriage with Kim Basinger, the '30 Rock' actor would be outnumbered.
Before finding out the sex of the baby, Thomas bet it was a boy although she didn't have preference whether she's having a son or daughter.
But the soon-to-be mother simply stated that it's probably best to just wait and see what name fits once they meet the little bundle of joy.
"I think you have to actually have to look at it once it pops out and say, 'Who are you? What is your name?'"
The couple wed in June 2012 and confirmed their baby news early last month.