The incidence of
low-back pain during pregnancy is thought to be about 50%. It occurs most commonly after the sixth month and can last until the sixth month postpartum. The major predictors are
back pain prior to pregnancy and multiparity. Several biomechanical and physiologic changes during pregnancy contribute to
back pain. As the woman's abdominal muscles are stretched and tone is diminished, they lose their ability to contribute to neutral posture. During pregnancy, production of the
hormone relaxin increases ten-fold. The
hormone creates
joint laxity, which not only allows the pelvis to accommodate the enlarging uterus, but also weakens the ability of static supports in the lumbar spine to withstand shearing forces. In the pelvis,
joint laxity is most prominent in the symphysis pubis and the sacroiliac joints. On physical exam, neither lumbar nor sacroiliac
back pain is generally associated with any evidence of
neurologic deficit or hip pathology. In cases of lumbar
back pain, the physical exam will be most consistent with discogenic
pain and/or facet
element pain. Therefore, a pregnant woman's
pain may be most pronounced on flexion and standing. Among the tests that can be used to evaluate
lower-back pain are the posterior pelvic provocation test; ventral gapping test; dorsal gapping test; sacroiliac joint fixation test; Patrick's test, or FABERE's maneuver (flexion, abduction, external rotation, and extension); and Derbolowski's test. The most common types of
back pain during pregnancy are lumbar
pain, sacroiliac
pain, and nocturnal
back pain.