During labor and birth your sacrum (the triangle at the base of your spine) has to move posterior (backwards) in order for the baby to move down into your pelvis. It's one of the reasons that we keep such a close eye on mobility in the RIGHT places. If sacrums don't move well---babies don't move well. If babies don't move well--vaginas have to make up for it. 😳😬😬😬
(that's a simplified version, but you get the idea. 😅😜)
