Back pain on 40 days of pregnancy is not necessarily a miscarriage. Low back pain in 40 days of pregnancy may be a precursor manifestation of miscarriage, but it is not common. Consider that it may be related to factors such as hormones, lesions around the lumbar spine, kidney disease, pelvic inflammatory disease, etc. It is recommended to judge the severity of your own low back pain or accompanying symptoms, and seek medical treatment if necessary. 1, hormonal influence: changes in hormone levels in early pregnancy lead to relaxation of joint ligaments and gradual increase in the size of the uterus, which may result in the manifestation of low back pain, but usually does not lead to miscarriage; 2, lumbar peri-vertebral lesions: common causes of lumbar pain in early pregnancy are lumbar diseases, especially patients with a history of lumbar disc herniation, lumbar strain, lumbar spinal stenosis, etc. Acute attacks may occur during pregnancy, which usually do not lead to miscarriage; 3, kidney diseases: such as nephritis, kidney stones, kidney tumors and other disease episodes, during which lumbar pain can occur, which is not related to the number of days of pregnancy and is coincidental. Patients need to be hospitalized to avoid triggering serious consequences. If the condition is not well controlled, there is a risk of miscarriage; 4. pelvic inflammatory disease: it can also lead to back pain, and at this time there is a risk of triggering miscarriage. Patients who also have discharge odor and vaginal bleeding at this time should seek medical attention in time to avoid the occurrence of pre-miscarriage. Miscarriage may present with back pain, but the more common symptoms are vaginal bleeding as well as abdominal pain. Therefore, if there are only symptoms of back pain and no other abnormalities, miscarriage usually does not occur. Pregnant women are advised to take more rest, observe more, and apply heat compresses as well as moderate massage as appropriate. If the back pain persists without relief, prompt medical attention is recommended.