Migration
Upon fertilization the zygote remains and actively divides in the ampulla of the fallopian tubes, until it reaches the morula stage (a simple ball of cells). It remains here due to the constriction of the fallopian tubes, which relax after three to four days allowing the morula to progress down into the uterine lumen. This delay allows a sufficient amount of time to elapse for glygogen to be released from the endometrial glands into the uterine lumen, as a nutrient source for the continually dividing zygote before implantation. If the zygote gets there too early it will die.
This is a physically incorrect diagram by Samantha Gummery, but it gives an overview of the migration of the egg.
