Pregnancy back pain may be the body hormone level changes, spinal biomechanical imbalance, lumbar muscle strain and other reasons. 1. Changes in hormone levels in the body: the hormone levels in the body change after pregnancy, more relaxin production, relaxin and estrogen synergistic effect can soften the pelvic joints, pelvic floor ligaments, so that the sacroiliac joints, pubic symphysis becomes lax, may produce the symptoms of low back pain. 2. Biomechanical imbalance of the spine: with the increase of pregnancy weeks and uterine growth, the lumbar spine increases in anterior convexity, and most of the weight is concentrated in the waist, abdomen and pelvis, and there is a tendency for the body to tilt forward, which may lead to intervertebral disc herniation and lumbar spine instability, and then the muscle tension on both sides of the spine is unbalanced, which triggers the symptom of lumbar pain. 3. Lumbar muscle strain: after pregnancy weight and increase the long-term compression of the uterus, may cause lumbar muscle strain, resulting in lumbar muscles, fascia, ligaments and other soft tissues chronic injury, the local production of aseptic inflammation stimulation of the symptoms of back pain. The causes of back pain after pregnancy are more, serious cases are recommended to seek timely medical attention.