If the egg is fertilized during ovulation, the fusion of the sperm and the egg forms a pronuclei then into a zygote (wherein the nuclei is already one or fused completely). It will then undergo the cleavage stage wherein the egg becomes a 2-celled to a 4-celled and to an 8-celled egg. Next is the morula stage as the cells grow larger in number. After that, the embryo starts to rise - the blastocyst stage. Last is the implanted blastocyst stage; the egg is now attached to the uterine lining.
