Vascular endothelial growth factor is the factor that causes increased capillary permeability and therefore the most serious manifestations of ovarian hyperstimulation syndrome. Dopamine agonists can both prevent and treat ovarian hyperstimulation syndrome by blocking expression of the vascular endothelial growth factor receptor. (Fertil Steril (R) 2012; 97:517-22. (C) 2012 by American Society for Reproductive Medicine.)