Common causes of back pain in pregnancy Changes that cause back pain during pregnancy Both lumbar pain and posterior pelvic pain may be caused by several factors related to changes that naturally occur in your body while pregnant. Common changes due to pregnancy include: Weight gain—pregnancy can cause you to gain as much as a quarter of your body weight, adding stress to the back and other weight-bearing structures. Center of gravity changes during pregnancy—secondary to weight gain, the weight is typically carried anterior (in the front) as well as posterior (behind). This change in your center of gravity creates: Muscular imbalances. These imbalances create strain on weight-bearing structures in the body and are more problematic if superimposed on existing imbalances (such as muscle weakness and inflexibility). Muscles that fatigue more quickly than usual. Muscle fatigue in turn often results in poor posture and/or makes poor posture even worse. Hormonal surges (relaxin and estrogen)—pregnancy related hormones can cause problems by creating joint laxity, especially in the pelvis. These hormonal surges, along with the additional weight and change in center of gravity, contribute to decreased joint support. Activities that can cause back pain during pregnancy Some or all of these factors can cause low back pain, especially with activities that create asymmetrical loading of the spine, pelvis and hips. Common activities that load the spine in an uneven fashion include: Walking and running Rolling over in bed Bending forward Twisting Lifting Navigating stairs