Oh, gosh, I don't know really.
Our situation is that DP, who's 35, tried first, because there was no reason to think she'd struggle. We did IUI with donor sperm and minimal medication, and we were so very, very lucky, and it worked. We have DD who is 9 weeks. I have had several miscarriages during a previous relationship (with a man, natural conceptions), so we knew I was a less good bet. I've been investigated on the NHS, and have several interacting issues, but I'm trying IUI. Last cycle was cancelled because I had an undiagnosed ovarian cyst. Trying again this cycle.
So, that's the context. I felt awful for DP when she was trying, because she was so convinced it'd work first time and be easy. And, even though she did get pregnant, her pregnancy was hard and her labour was very hard (she has PTSD and she and DD nearly died), so I felt guilty for not having taken that burden - even though of course it was her choice. Then, I felt guilty last month for not being able to try. And I do feel worried that I may not be able to sustain a pregnancy - especially since she would want to try again, and I know it was so hard on her last time.
That all sounds very negative. I think from my perspective, what DP could do to help would be just to accept that I worry for different reasons from her, and they're valid too. We all react differently. You just need to listen to the partner who's currently trying - even if they're being totally hormonal and strange!
I just asked DP and she says having a back up plan is reassuring. We talked about what we'd do, when we'd stop trying, how we'd feel - that helped.