hubby getting checked

So I'm poking for advice on how to ask my bf to get his swimmers checked. We have been trying for about 7 months now and nothing. I have been checked and looked at and my body is good and ready. So he made a joke one time "well maybe it's me" and now I keep obsessing over it. He thinks if we find out there's something wrong with him then I'll hate him. I'm a big believe that when it happens is when it was meant to happen and I have no worries so I don't want him to worry but how do I talk about it with him and ask him to check with out making him feel incompetent