It often feels like there are a lot of rules about what you can and can't do when you're trying to get pregnant , and especially if you're pursuing in-vitro fertilisation (IVF). For example, you might have heard that you're not supposed to work out too much when you're getting IVF, which sounds counterintuitive. But as it turns out, there's a physiological reason why you're supposed to be somewhat cautious with exercise if you're also getting IVF.