information:extraction, structural:expansion
In pregnancy and childbirth

In later stages of pregnancy the fetus 's head aligns inside the pelvis. Also joints of bones soften due to the effect of pregnancy hormones. These factors may cause pelvic joint pain (symphysis pubis dysfunction or SPD). As the end of pregnancy approaches, the ligaments of the sacroiliac joint loosen, letting the pelvis outlet widen somewhat; this is easily noticeable in the cow.

During childbirth (unless by Cesarean section) the fetus passes through the maternal pelvic opening.