Early pregnancy does not cause sciatica because the fetus is very small and the uterus does not cause too much compression and occupancy in the pelvic cavity, which will not produce too much load on the lumbar spine or too much compression on the pelvis. At the same time, the physical mobility of pregnant women in the early stage of pregnancy is relatively strong, so there will not be any inconvenience in movement, and the sciatic nerve in the legs will not be significantly squeezed or strained. Therefore, sciatica will not appear in the early stage of pregnancy, but as pregnancy becomes longer, the uterus gradually increases, resulting in pelvic compression and increased load on the lumbar vertebrae, and the inconvenience of movement may also lead to strain or injury to the sciatic nerve in the lower limbs, and sciatica may appear.