Is it permissible to sell fertilized eggs, which are sold at a higher price than regular eggs due to the characteristic of being fertilized, knowing that selling a fetus inside an egg is forbidden due to gharar (excessive uncertainty), by analogy with the permissibility of selling a pregnant animal for more than its price due to the characteristic of pregnancy?

It is permissible to sell eggs unconditionally, whether fertilized or unfertilized, due to the possibility of benefiting from them in any permissible way. As for selling fertilized eggs specifically for hatching, this involves gharar (uncertainty) and jahalah (ignorance) which invalidate the contract, and it takes the ruling of purchasing what is in the bellies of animals. It is permissible to sell eggs after they have been incubated.