the ovarian vein often displays incompetent valves. this has been observed more often in women with a higher number of previous pregnancies. pressure from the baby might hinder the return of blood through the ovarian vein. it has to be noted however that dilation of the urinary tract is a normal observation in pregnancy, due to mechanical compression and the hormonal action of progesterone. ovarian vein dilatation might also follow venous thrombosis (clotting inside the vein).