Studies have shown that the sacroiliac joint (SIJ) may develop some looseness after the birth of a child. This is referred to as postpartum SIJ instability. "Instability" means the joint isn't held steady by the muscles and ligaments that normally support the joint. The most common sign of a problem like this in the SIJ is pain or difficulty raising the leg from a flat surface.

You may also notice some changes in the way you breathe as you try to complete this task. Some people stop breathing altogether while trying to lift the leg. Others increase or decrease their rate of breathing.

Physical therapists think this happens because the stomach muscles are out of sync with the diaphragm (breathing) muscle. Which comes first: a change in the sacroiliac joint from the birthing process, or changes in the muscles? No one knows just yet.

You should report these symptoms to your doctor. If you have a sacroiliac joint problem, your doctor will likely have you work with a physical therapist.