HI, I have read your query & understand y6our concern. Pregnancy hormones cause loosening of pelvic ligaments. As a result the pelvis is stretched due to growth of fetus .. this leads to pain in back in pregnancy. Also as the baby grows, the abdominal weight increases. So there is much more load in front of body.. making imbalance due to shifting of line of gravity.. the back muscles stretch the line of gravity back to normal by contracting & pulling the body back. This creates lot of stress to back muscles & so the pain. * this can be managed by doing pregnancy yoga exercises to strengthen the back muscles. * back pain also follows calcium & vitamin D deficiency. Replacement of these controls the pain. - some times vaginal/ pelvic infection or inflammation can cause the back ache. This needs a gynecologist s advise / investigatios & specific treatment. ** you should consult your gynecologist for proper guidance after checking you up. thanks.