Typically within the first month you will decide whether or not they are fertile. Fertile eggs will remain solid and white. Infertiles will begin to shrivel and turn yellow or mold. After a month, you are supposed to be able to see arteries within the egg if they are fertile. However, do not throw away eggs that haven't molded, even if you think they are infertile! I know that babies can still hatch out of an odd-ball egg