The Piranha 3D model and actress is expecting her first child with Scottish former rugby player Thom Evans, and announced the pregnancy five months after she began dating the sportsman.
However, speaking to Hello magazine, the 31-year-old said that despite the quick progression of their relationship, she feels everything is falling into place.
"This baby is not the result of me suddenly becoming broody because I have hit my 30s. It is simply that I have met someone that I am happy to share that responsibility with," she explained.
"When you discover you are pregnant, you ask yourself, 'Am I in the right situation to do this in the best possible way I can?' And with Thom, as much as I love him as a boyfriend and someone I fancy, I have to say to myself, 'This man is going to be the father of my child. Can I rely on him? Is he responsible? Is he going to take care of me?'
"All of these questions have put a huge pressure on Thom - and on me too. But every time I've considered these things, I realise I can tick that box."
However, she played down suggestions that the couple could marry soon.
Brook said: "One thing at a time. I don't think it is impossible by any means, but to love someone for the rest of your life is a hard thing to promise.
"I think having a baby with someone is a far greater commitment," she added.