The uterine veins are thin-walled and easily collapsed. During inversions, the uterus is pulled towards the head by gravity, causing the broad ligaments to be stretched. This can cause stretch and partial collapse or occlusion of the thin-walled veins, while allowing the uncollapsed arteries to continue to pump in blood. Thus, more blood enters the uterus via the arteries than can be carried away by the veins. The vascular congestion that results can lead to increased menstrual bleeding.
Hindu philosophy teaches that during menses the direction of energy is down and out of the body.
This flow should not be obstructed or reversed as it is in inversions. There have been numerous misconceptions about why to avoid inversions. This tissue responds to the hormones of the fertility cycle. When menstruation occurs, these foci of endometriosis break down and bleed just as the uterine lining does. But since there is no exit for this flow, scarring and adhesions result.