I've done this too, and my therapist and I have talked a lot about why it's difficult to bring a particular topic up before we even get to discussing the topic.

It hasn't always made it easier to actually say the words when the time comes, but the "warm up" period is helpful in getting me used to the idea of talking about it.

Usually my greatest fear in bringing up a topic has to do with worrying that my therapist will judge me about it. Not that that's ever happened before, but it seems to be the way I'm programmed. Do you have a sense about what your fears are around discussing the topic?