Back pain in the first trimester of pregnancy may be caused by the gradual enlargement of the fetus, calcium deficiency of the pregnant woman, and changes in hormone levels in the body, etc. For details, you can go to the hospital for relevant examinations. 1. Gradual enlargement of the fetus: the fetus grows gradually in the uterus of the pregnant woman, which presses on the surrounding nerves and tissues, leading to back pain in pregnant women. 2. Calcium deficiency of pregnant women: During the development of the fetus, calcium is needed during the growth of fetal bones, and pregnant women may suffer from back pain due to calcium deficiency. 3. Changes in hormone levels in the body: progesterone, estrogen, and human chorionic gonadotropin will increase after pregnancy, and pregnant women will experience many symptoms due to the changes in hormone levels in the body, such as low back pain, vomiting, dizziness, drowsiness, and other reactions. Pregnant women with back pain in the first trimester of pregnancy may also have other causes (such as herniated anterior vertebral discs, lumbar muscle strain, etc.) It is recommended to go to a regular hospital for relevant examinations, to clarify the cause of the disease and then cooperate with the doctor’s treatment.