This is a specific type of lower back pain which is associated with shooting pains down the back of the thigh. It can sometimes reach the sole of the foot. It is due to pinching of nerves as they exit the lower spine. In pregnancy this can occur due to the change in posture and fluid retention. Another rare cause is herniation of the lumber discs.
Treatment involves physiotherapy which concentrates on core strengthening to improve posture and sciatic stretch exercises to minimise swelling of the nerves as they exit the spine.
Disc herniation is a little harder to treat as none of the treatments are particularly helpful. Women often need rest and to take large doses of pain killers.
Surgery is almost never indicated in pregnancy. Sciatic pain can be associated with sensory loss, and in severe case, may result in muscle weakness.
If neglected, these changes may become permanent, so initial treatment with physiotherapy is important to avoid an increase in severity.