I've heard from many people that the testicles stop producing sperm altogether on hrt, and thus one can become infertile fairly easily. However, my wife was on hrt for 11 months total, and about 5 months after she went off it, I got pregnant and miscarried. Wasn't expecting that at all... I thought she must be sterile. Now she is holding off on restarting hrt until she is able to afford storage.
SD