Normally the blood is pumped from the legs, through the veins in the pelvis and abdomen to the heart. The blood normally flows from the ovaries through the ovarian veins. The right ovarian vein joins the inferior vena cava and the left ovarian vein joins the left renal vein.

When the valves in the vein stop working or there is obstruction to the flow of the blood in the veins going back to the heart, the blood then flows backwards (i.e., the wrong way, away from the heart). This causes the varicose veins in the pelvis around the ovaries, vulva/vagina and down the inner thigh and legs, causing PCS.²