Low back pain in pregnancy may be caused by the effect of hormones, changes in body shape, hydrosalpinx and other reasons. 1. The effect of hormones: after pregnancy, the body secretes more estrogen and progesterone, which makes the ligaments of the body loose, causing the joints to become loose or misaligned, thus leading to back pain. 2. Changes in body shape: After pregnancy, the uterus enlarges, the abdomen bulges, the pregnant woman’s body tilts backward, and the lumbar vertebrae are overextended. Such a special body shape makes the back muscles and ligaments of pregnant women continuously tense, resulting in low back pain. 3. Hydrosalpinx: Due to the enlargement and rightward rotation of the uterus, the fallopian tubes are compressed, which may lead to hydrosalpinx, which in turn causes back pain. Pregnancy back pain may also be caused by other reasons, patients are advised to seek timely medical attention to clarify the cause of the disease, in order to prevent affecting the fetus and maternal health.