The pain on both sides of the buttocks in the fourth month of pregnancy may be normal, it may be caused by the increasing uterus compressing the sciatic nerve and spinal compression, or it may not be normal, it is caused by the lack of calcium in the organism. 1. Sciatica: four months pregnant is the stage of mid-pregnancy, with the increase of pregnancy weeks and the enlargement of the uterus, it may compress the sciatic nerve, both sides of the buttocks will have pain manifestations, you can try to relieve by changing the position. 2. Spinal pressure: the uterus grows rapidly in the fourth month of pregnancy, the pressure in the abdominal cavity increases, and the forward protruding abdomen increases the pressure on the spinal area, which also triggers the symptoms of pain on both sides of the buttocks. 3. Calcium deficiency: four months of pregnancy due to the rapid development of the fetal body, pregnant women will increase the demand for calcium, supplementation is not timely will lead to osteoporosis, the appearance of pain on both sides of the buttocks, can be improved by taking oral calcium supplements. The causes of pain in the buttocks on both sides in the fourth month of pregnancy are more varied, and it is recommended to consult a doctor in time for serious cases.