Sheree and Hayseed, you've both nailed it on the head. It really is something that can't be underestimated.

IMHO I think that the more a woman wants (and actually needs) to have a baby, the worse the stress. I have a close friend who underwent IVF (got pg on her 3rd attempt) but didn't stress too much about it...for her, she was never clucky and I get the impression that a lot of her motivation was the fear of 'missing out' on having a baby and also because her DH really wanted one. So I think she would have been fine (though a little pee'd off about spending all the money for no return) if things hadn't worked out for her.

The stress comes from the failure and the realisation of the possibility of not being able to have the longed-for baby.