The appearance of blood in the fourth month of pregnancy may be caused by overwork, signs of pre-miscarriage, vaginitis, etc. The symptoms can be improved by general treatment, fertility preservation treatment and medication. 1. Excessive exertion: If a pregnant woman is overworked in the fourth month of pregnancy, it may lead to the appearance of blood. You can go to the obstetrics department of the hospital for an obstetric ultrasound to see the development of the baby, if it is normal, it is recommended to pay attention to bed rest, minimize the activities, avoid sexual life and strenuous exercise. 2. Pre-eclampsia signs: four months pregnant, such as the appearance of blood, accompanied by paroxysmal abdominal pain, may be suggestive of pre-eclampsia possibility, the need to consult a doctor in a timely manner, ultrasound to clarify the situation of the fetus to follow the doctor’s instructions for the preservation of the fetus treatment. 3. Vaginitis: If a woman in the fourth month of pregnancy, combined with vaginitis, there may be a small amount of blood. The nature of the vaginitis should be clarified and the appropriate medication should be used, which can be directed to the cause of the disease under the guidance of the doctor. Pregnant women with blood in the fourth month of pregnancy should go to a regular hospital in time to identify the cause of the disease and take targeted treatment under the guidance of a professional doctor.