Really, msnana? When you click on the baby boost in the game, it infers that if you give it more than once that it will reduce the effectiveness of it. For some reason, either from what that says or from reading something here on this forum, I assumed that if you gave it more than once it could make them infertile instead. I've only given each one the shot once. Although, that's just the females. I have only given the shot to one male so far and that was only because the doctor's report said he needed it.