Subinvolution of the uterus is a common complication after childbirth. Under normal circumstances, after childbirth, due to the contraction and retraction of the uterine muscle fibers, the blood vessels in the myometrium are narrowed or even embolized, which significantly reduces the local blood supply. The uterine muscle cells are ischemic and autolyze and gradually shrink, and the cytoplasm decreases. As a result, the volume of the uterus is significantly reduced. The placental detachment surface in the uterine cavity shrinks accordingly as the uterus gradually shrinks. In addition, the regeneration of the endometrium repairs the detachment surface. The uterus usually returns to a state close to the non-pregnant state 5 to 6 weeks after delivery. This process is called involution of the uterus. When the above-mentioned involution function is hindered, subinvolution of the uterus occurs.