The causes of left side buttock soreness in pregnancy may be caused by keeping a posture for a long time, weight gain, and calcium deficiency in the body. 1. Keeping a posture for a long time: Keeping a limb in the same sitting, lying down or standing for a long time, with the left limb as the main one, and overloading and straining, the symptom of left buttock soreness may appear. 2. Weight gain: with the increase of pregnancy weeks after pregnancy, the weight will continue to increase, the center of gravity will move forward, the spine protrudes forward, affected by the hormone increase in the body, the lumbar muscles, intervertebral discs become less stable, squeezing the nerves caused by the left side of the sciatica, but also the symptoms of the left side of the buttock soreness. 3. Calcium deficiency: after pregnancy, the fetus and the mother’s demand for calcium increases, calcium deficiency in the body will decrease the concentration of calcium in the blood, which may cause muscle spasms, contractions, manifested in the left buttock pain symptoms. There are many reasons for the left buttock pain after pregnancy, if the symptoms are serious, we recommend timely consultation.