Katie is expecting her second child with Kieran, who had an affair with her best friend, and says her confidence is rock bottom and that she has questioned whether his behaviour was the result of her weight gain.
The former glamour model appeared on Loose Women today and told viewers: "I don't mind anyone else criticising me because nobody's perfect but when it's at home and your other half...
"I'm insecure at the moment, as I've put on 4st....my husband cheated on me and I've got that into my head."
She added: "As you know you can't help what your body is going to do. I've been pregnant the whole time I've been with [Kieran]. He only knows me pregnant.
"He doesn't actually know me small. It's my own fault [that I keep getting pregnant] though!"
The Loose Women panel - Janet Street Porter, Myleene Klass and Andrea McLean - gasped in shock when Katie said this and told her she should not blame herself.
Days after discovering Kieran had cheated on her, Katie pulled out of a scheduled appearance on Loose Women. Her guest hosting slot was then rescheduled to today (20 June).
Soon-to-be mum-of-five Katie stunned fans on 7 May when she announced she was to divorce Kieran after discovering he'd been having a "sexual affair" with her best friend Jane Pountney.
Kieran has since admitted the affair, along with Jane, who said she "deeply regrets" her actions.
Earlier this week, Katie appeared on her new FUBAR Radio show and claimed Kieran had also cheated with a second mystery woman.
While on air, Katie said his affair was uncovered after she made Kieran take a Jeremy Kyle-style lie detector test.
She then confirmed that he is seeking help and said their marriage may not be over yet: "He's been with my best friend and all I can do is deal with the situation and get him help," Katie explained.
"If a friend was telling me what had happened to me, I'd be like, 'Get rid of him'. You have to be adult and assess the situation though.
"Was it normal? No it bloody wasn't! So he can't be that normal in the head. I can only stick by and see what happens. I have to see that he's making a difference."
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