What is the primary cause of subinvolution of the uterus following delivery?

Subinvolution of the uterus refers to the failure of the uterus to return to its pre-pregnancy size and condition after childbirth, which is typically characterized by a process of contraction and tissue repair. The primary cause of subinvolution is retained placental fragments.

After delivery, it is crucial for all placental tissue to be expelled from the uterus to facilitate complete involution. If any fragments remain, they can interfere with the normal healing and contraction process of the uterus. This retained tissue can lead to prolonged bleeding and potential infection, which can further contribute to subinvolution and complicate recovery.

While infection of the uterus, uterine atony, and hormonal imbalance can influence uterine health and healing postpartum, they do not specifically cause subinvolution in the same direct manner that retained placental fragments do. Uterine atony, for instance, primarily leads to hemorrhage rather than subinvolution, and hormonal changes post-delivery are part of the natural adjustment process rather than a primary cause for this condition.