Back pain associated with pregnancy can be generally placed into one of two categories, low back (lumbar) pain and pelvic pain.  Low back pain in pregnancy feels similar to the pain experienced with a muscle strain or sprain.  The pregnant women may develop sciatic pain, if there is compromise of the nerve roots coming out of the spine at the level of the low back.  An increase in the curve of the low back will result in narrowing of these openings. If a woman enters pregnancy with preexisting degenerative changes or disc pathology in the low back, the increased lumbar curve along with the preexisting degenerative changes increases the risk for developing sciatic pain.  The pregnant women may also develop radiating leg pain due to the expanding fetus and unterus compressing the nerves which run behind the uterus. 

Pelvic pain is different from low back pain.  It tends to be located at the waistline extending to the lower abdomen and hip regions.  Pain which arises from the pelvic region rarely goes below the knees.  It can occur on one or both sides.  Pregnant women are more prone than non-pregnant women to develop pelvic pain.  There are many things which will cause pelvic pain in the pregnant women.  The pain may be mechanical in nature arising from changes in the pelvic contents in response to an expanding uterus.  There can also be obstetric causes of pelvic pain, which have absolutely nothing to do with the spine.  The causes of pelvic pain may be associated with back pain, but the pain is not actually originating from the spine.  There may be situations, where there is both low back (lumbar) and pelvic pain.