Katie, 35, said that she has been suffering from anaemia and is a lot bigger than she was during her previous three pregnancies.
Speaking on ITV1's Daybreak, Katie said: "It's the worst pregnancy. I've had lots of problems with being anaemic, low platelets, [I'm] a lot heavier than I was before.
"But it's the fourth one so I know what to expect."
Katie appeared on the breakfast show to talk about her new book He's The One. She also confirmed that her third husband, Kieran Hayler, is The One.
"I have to say, obviously it's my third marriage, [but it's] third time lucky. This one is The One.
"Oh, he's so good. He's so normal and he goes to work. That's really important. He's got a normal job and a lovely family, it's just perfect."
Along with He's The One, Katie is due to release her latest autobiography, called Lipsticks, Love and Lawsuits, in October.
The former glamour model also told Daybreak viewers that her new autobiography will be "disturbing and emotional" and will follow on from her marriage to cage fighter Alex Reid.
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