If an ovum is not fertilized, the female body shed the lining of the uterus in a process called menstruation. Not releasing the non-fertilized egg will cause complications to the uterus of women. Think of it this way: Every month, the uterus readies the body for pregnancy through setting up a wall on the uterus where the fertilized egg is cradled and nourished. When ovum is not fertilized, the body will release the build-up in the lining through monthly menstruation to clear the uterus from possible infection.