The former Liberty X singer celebrated her 32nd birthday and first wedding anniversary with husband Hugh Hanley by revealing the news on Twitter this afternoon.
Heaton wrote: "Happy birthday/1st yr anniversary/ and mummy day to me! I can feel it doing press ups already! LOL! Best bday present ever! Xxx"
As her 37,000 followers rushed to congratulate her, the Celebrity Big Brother star replied: "Thank u all so much for your kind messages... such an amazing time."
Dancing On Ice winner Sam Attwater was among the well-wishers, prompting Heaton to joke about having "an excuse" to pull out of the upcoming Virgin Active London Triathlon that they were both training for.
"Hardly. I've got work," Attwater responded. "Whereas you got knocked up just so you didn't have to run 5k. Disgraceful behaviour! Ha. X"
Heaton went on to describe an "amazing" photoshoot for today's edition of OK! magazine, which includes an exclusive interview about her pregnancy. She also proposed to its rival publication Closer the idea of a weekly mother-to-be diet and exercise column.
Heaton, who separated from first husband Andy Scott-Lee in 2008, tied the knot with Hanley in the Bahamas.