You get sciatica when there is any pressure on the sciatic nerve. This nerve starts in the lower spine and ends in the thigh. If there is any compression of this nerve you will experience a radiating pain that can travel from your buttocks to your hip down to your thighs and legs. Sometimes pregnant women may also get this kind of pain. This is because low back pain in pregnancy is very common. It happens due to muscle tension unstable joints and pelvic bone pain. If you are pregnant you may also suffer from a condition called sacroiliac (SI)