From very old ceremonies these parties start from the bride's mother and father. Usually when the newly wed are back from their honey moon or after one or two weeks after the marriage ceremony, bride's mother will invite the newly wed and the groom's in-laws ,grand parents and sometimes even cousins, aunts and uncles . The bride's mother will call the members of the groom's family and invite them to the party personally and a gift is prepared for the newly wed before hand.
In Iran when the daughter of the family gets married, her family concider the groom as their own son and they think of him as a new member of tha family. That's the reason that the bride's family throw the first party. There's an old saying in Iran which says that the groom will be influenced by the bride's native land because of too much companionship with the bride's family.