Please, put some thought into this venture before you proceed with a breeding that could end up a nightmare. Infections transfer from breedings.
Complications can and do happen, and bitches do die before, during and after whelping.
A Yorkie should never be alone as the Whelping time draws near, very few can Whelp without assistance. To see a new Born with a birth defect is heart breaking, and it has to be put down. It must be done and you can not let it suffer. This can be extremely hard on your Bitch also. Should this happen you may need to Tube Feed.