The hormonal changes of menstruation, pregnancy, and lactation can affect the integrity of the ligament support around the SIJ, which is why women often find the days leading up to their period are when the pain is at its worst. During pregnancy, female hormones are released that allow the connective tissues in the body to relax. The relaxation is necessary so that during delivery, the female pelvis can stretch enough to allow birth. This stretching results in changes to the SIJs, making them overly mobile. Over a period of years, these changes can eventually lead to wear-and-tear arthritis. As would be expected, the more pregnancies a woman has, the higher her chances of SI joint problems. During the pregnancy, micro tears and small gas pockets can appear within the joint. [This paragraph needs citations]
These accessory movements of the sacroiliac joint are not under voluntary control; they are necessary, however, for full painless function of the joint and full range-of-motion of the joint. Sacroiliac Joint dysfunction signifies a loss of JOINT PLAY movement. The existence of joint play movement is necessary for pain free voluntary movement to occur. If the JOINT PLAY movement is found to be absent, this movement must be freed before functional voluntary movement can be fully restored. This is best done by skilful manipulation.