Low back pain is a relatively common symptom during pregnancy, the pain symptoms and parts are different, and the causes of low back pain will also be different. Most of them are caused by physiological reasons, but there are also individual pregnant women who may have back pain caused by pathological reasons. Common analysis is as follows: 1. due to changes in estrogen and progesterone: estrogen and progesterone secretion will increase significantly after pregnancy, which often makes the pelvis and ligaments become lax to meet the needs of fetal growth and future delivery. However, because the ligaments are relaxed, the elasticity is reduced, so it will cause lumbar pain due to strain; 2, due to excessive lumbar spine weight: is the main reason for the left lumbar pain of pregnant women, with the increase in fetal age, the fetus gradually increases, the attached placenta and amniotic fluid will also increase, which will increase the burden on the lumbar spine. In order to maintain balance, pregnant women often contract their lumbar muscles when standing, and over time will cause lumbar pain symptoms due to lumbar fatigue; 3, due to left-sided sleeping position: in late pregnancy, pregnant women sleep in the left-sided position to increase the blood flow of the placenta and improve the fetal intrauterine hypoxia. So pregnant women often take this sleeping position to sleep. If you sleep in a left-sided position for a long time, it will also lead to an increase in the weight of the left side of the waist, the symptoms of waist pain; 4, due to insufficient calcium intake: the growth and development of the fetus needs a lot of calcium, if the pregnant woman does not take enough calcium to meet the fetal development, pregnant women are prone to calcium deficiency, which will also cause left waist pain;