2, poor uterine regeneration: after miscarriage, patients do not have sufficient rest, resulting in slow recovery of the uterus and poor contraction of the uterus, resulting in bleeding in the uterine cavity, which will show fluid in the uterine cavity when the ultrasound is repeated; 3, prolonged bed rest: some patients stay in bed for a long time after miscarriage, which is not conducive to the discharge of blood in the uterine cavity, because after activity, with the effect of gravity, the blood can be discharged from the uterine cavity. If the ultrasound shows that the fluid in the uterine cavity is purely blood or blood clots, you can take appropriate drugs to promote uterine contraction or hemostasis as prescribed by the doctor to enhance uterine contraction, promote fluid discharge and reduce intrauterine bleeding. If the blood flow signal shows intrauterine residue >1cm in thickness, it indicates that there may be intrauterine residue and it is necessary to follow the doctor’s advice and perform another uterine clearance operation.