Why does back pain and postural changes of pregnancy occur?

Patients tell me all the time as they get further along in pregnancy their back pain worsens.  More than 50% of women complain of back pain during pregnancy.  The additional weight gain in pregnancy can affect the centre of gravity which leads to backaches and back pain. Women experience a progressive increase in the anterior convex shape of the lumbar spine during pregnancy. This change, better known as lordosis, helps keep the center of gravity stable and over the legs as the uterus enlarges (see below). Late in pregnancy, aching, weakness, and numbness of the arms may occur secondary to an expected change of an anterior positioning of the neck and hunching of the shoulders in response to exaggerated lordosis.  As a result of these positional changes traction on the ulnar and median nerves causing numbness in the arms and hands.

Lumbar lordosis of pregnancy.

 
Other postural changes that occur are joint laxity and shifting center of gravity which contribute to an increase in gait unsteadiness.  Some have described this as if “they have just gotten off a horse”.  These changes are most exaggerated in later pregnancy.  The pelvis and the ligaments that support it are stretching and expanding in anticipation of delivery.  For those women that have debilitating back pain, massage, heat, back strengthening exercises, acetaminophen, and physical therapy can serve to ease the pain.  Always discuss any unusual, persistent or worsening symptoms to your health care provider.