Unfortunately, mid and low back pain during pregnancy is common but is not normal. As the baby grows, your center of gravity changes and relaxin production increases, it is common for the pelvis to excessively tilt forward causing pressure on the joints and discs of the mid and low back. The cumulative affect of improper sitting posture, poor work habits, incorrect lifting, lack of proper exercise and other lifestyle-related factors are all magnified by the effects of pregnancy. All of these factors cause repetitive low level stress on the spinal joints and associated musculature and eventually pain. When this occurs, the surrounding back muscles go into spasm to protect the stressed or injured tissues of the back. This can occur both in previously healthy joints and discs and in ones that have had prior issues.