Poor posture is a common cause of backache in pregnancy. The growing weight of the uterus changes the center of gravity and instead of standing straight, women pull their shoulders back, causing an increased curve in the back. To straighten up, you will need to tilt your pelvis forward and lengthen the body keeping hip, elbow and shoulder in a straight line. You can practice this against a wall, checking the amount of curve in your spine with your hand. In proper posture, you will find your stomach and behind stick out less.
When the abdominal muscles pull the pelvis into the proper alignment, the pressure on the back is decreased and the bulge in the belly seems to shrink.
Core Muscle Strength
Weak abdominal muscles cause the back to work harder to support the weight of your torso. Spend a few minutes a day doing exercises to strengthen your abdominal muscles. Try prenatal yoga or pilates.
If you have a backache and need relief, try using Pelvic Rocking. This exercise will stretch the back and can give you instant relief from lower backaches. You can also change position to Tailor Sitting which lets you stretch the back instead of putting extra pressure on it.