When pelvic joints start to loosen (to allow easier passage for your baby during delivery) and especially later in pregnancy, when extra weight shifts your center of gravity, adding stress to your back muscles, you may experience mild achiness. To help minimize back pain, stay away from shoes that are high-heeled, instead wear low-heeled shoes with good arch support. Practicing proper lifting techniques can also help. Always bend at the knees, not at the waist to avoid straining your back further. Try to stay off your feet whenever you can, elevating them with a foot stool and avoid standing for long periods. Warm baths and back massages are also a great way for temporary relief. In your third trimester, may want to contact your doctor or midwife if you have persistent back pain, because it could possibly be a sign of preterm labor.