How to get your partner to get his swimmers checked?

My husband and I have been together for 6 years. Last month he adopted my daughter who he has been in her life since she was young. He missed out on really raising her as a baby. He and I have been married for over a year and have never use protection of any kind after the first two years. We have been trying a little harder over the past year but nothing. I am calculating my cycle and everything. I have said that I think he maybe should go get checked out. He brushes it off and I am not about to make him feel bad but I am really worried it is him. How do you talk your partner into getting checked without killing him. He is a power lifter and does MMA I feel like this has taken a toll on his body.