Final answer:
The uterus undergoes involution and contracts to return to its pre-pregnancy size during the postpartum period. Breastfeeding and the expulsion of placental fragments also aid in this process.
Step-by-step explanation:
During the postpartum period, the uterus undergoes several changes. Firstly, the uterus goes through a process called involution, where it contracts to return to its pre-pregnancy size. This is facilitated by uterine contractions, which continue for several hours after birth. Additionally, the uterus expels any remaining placental fragments to prevent postpartum hemorrhage. Finally, breastfeeding also helps in involution and aids in the return of the abdominal organs to their pre-pregnancy locations.