Accumulation of blood in the third trimester of pregnancy may be caused by the cause of preeclampsia. The occurrence of preeclampsia in early pregnancy, due to the occurrence of paroxysmal contractions, can cause the fetal membrane and the uterine wall to be peeled off, and the blood sinus is open, which can cause the accumulation of blood in the uterine cavity, and even vaginal bleeding. At this time, you need to follow the doctor’s instructions to pay attention to bed rest, and under the guidance of the doctor to use progesterone, dydrogesterone and other drugs to protect the fetus treatment. In this case, regular ultrasound examination is needed to check the area of blood accumulation and the absorption situation. During pregnancy, you should pay attention to rest, avoid strenuous exercise, and take obstetric examinations on time. When there is blood accumulation in the third trimester, you need to consult a doctor in time to find out the cause and deal with it actively.