If you want your spouse to get pregnant, wear boxers. Heat is not good for sperm production.
Years ago I read a study about men who worked in pizza kitchens. Most of them had a very low sperm count because of the heat. They did a study to try to get them to wear a refrigerated device to keep their sperm cool. All the volunteers dropped out of the study within 3 days.
That is hilarious, but has me thinking about vibrations. No, not those vibrations! Long haul truckers and freuent motorcycle riders experience continual vibrations most people are not subjected to otherwise. I know long haul trucers and motorcyclists can exerience bladder/urination problems from the constant vibration. Now I wonder if that affects fertility. Hmmm.
I willsay this much. Briefs as birth control would be awesome, if it was that easy.