The picture caption read how she was "enjoying precious moments with bump" and added "can't wait to meet you".
Michelle has been taking it easy since leaving the TV3 showbiz programme last May.
She had been filling in for Aisling O'Loughlin, while she was on maternity leave with her second baby and Michelle had gone down a storm with viewers.
Donegal native Michelle will give birth in her adopted city of London, where she moved over two years ago and she said how she can't wait to become a mum.
The ex-model, who used to anchor her own show on Phantom, said she feels extremely lucky to have gotten pregnant so easily.
"I'm feeling great. I've been so blessed, I've had the best pregnancy. I was never sick and only now I'm getting tired in the evenings," she said.
"But all along it's been amazing. I was more worried that I wouldn't be lucky enough to get pregnant, because so many people struggle to.
"Some people do take it for granted and I was never one of those because I love children so much. I would've died if I couldn't have had a baby so yeah, that was my priority.
"Then once I found out, it was that initial thing of going, 'Oh my God am I ready?'"
Michelle also plans on taking a good deal of time off after the birth as she puts her career temporarily on the back burner.
"I want to be able to bond with the baby and build the relationship," she said.
"You can't put your life off because of jobs. I just always wanted to be a mum and I thought: 'Whenever it's the right time I'll take my blessings'."
The presenter went on to say that moving to London was the best decision she ever made in the wake of leaving the now-defunct radio station Phantom.
"I was very low, I reached a really bad place. I couldn't deal with it," she said.