The 33-year-old, who already has 19-month-old daughter Faith with fitness instructor Hugh, tweeted:
‘I am thrilled to announce I am @OK_Magazine new health & fitness columnist .. & guess what? I get to blog about my pregnancy .. ; ) ....
‘..yup, myself and @hughhanley are thrilled we are expecting a mini Michelle or Hugh. Check out @OK_Magazine to find out why it was a shock..
..this is a very exciting time for us after everything that's happened.. Thank you as always for your love & support! Whoop whoop! Xxxx’.
Michelle had a double mastectomy last year after she learnt she carried the BRCA2 gene, giving her an 85% of developing breast cancer.
The pregnant mother-of-one will deliver the baby by caesarean as she suffers from the heart condition Mobitz Type 1.
‘It's a miracle, I've had three scans, she told a UK magazine.
‘I've seen the heartbeat twice. But it hasn't been without some drama.’
Speaking about new big sister Faith, she added:
‘She knows there's a baby in me. When I say: ˜Where's the baby?' she comes and strokes my belly. She gave the dummy to my belly button the other day.’
Michelle has also confirmed her plans to have her ovaries removed following the birth of her second child, to avoid the risk of ovarian cancer.