OPRM1 and ovarian hyperstimulation syndrome: Lunger et al. [26] reported the presence of main opiate receptor-1 (OPRM1) on human granulosa cells and found its blocking significantly reduced granulosa cell-derived VEGF levels in granulosa-luteal cells; thus raising a possibility of disturbed ovarian levels of growth factors as basis for development of OHSS; irrespective of the receptor-type for initiation of response.