From what I understand, but I may be wrong...I am sure someone knowledgeable will correct me if this is incorect but:
It is
almost impossible/incredibly difficult to get a girl pregnant while you are on Testosterone. People get pregnant all the time while their mate is on testosterone because "it only takes 1 swimmer" but the chances are still very very low. Taking HCG while on Testosterone only keeps your testicles functioning and makes recovering fertility a lot easier should you choose to stop testosterone to try and have kids. When I first started TRT I was very concerned about the fertility part of it and I eventually want to have kids one day. My Doctor had a sperm analysis done before I started and I was indeed fertile and he said taking HCG during TRT will help insure fertility and when the time comes to have kids he said he would have me come off of testosterone temporarily and prescribe me Clomid and getting my girl pregnant should not be a problem since I was fertile before I started TRT and I took/have taken HCG throughout my TRT. Clomid basicly jump starts your testicles and whatever natural testosterone production you have and the HCG makes the "jump start" easier and more effective. Double check me to make sure this is all correct with your Doc but if I remember correctly this is the way my Doctor explained it to me.
Best of luck having kids!
Keep us posted on what happens because I am going to be in your shoes one day soon