What occurs if the egg has not been fertilized it when it reaches the uterus?

If the egg has not been fertilized when it reaches the uterus, it will not implant in the uterine lining. Instead, hormonal changes lead to the degeneration of the egg and the shedding of the uterine lining, resulting in menstruation. This typically occurs about 14 days after ovulation if pregnancy does not take place.