While the aforementioned finding provide support for a modulatory role of hCG in the immune response during pregnancy and strengthens the concept of a distinct regulation of lymphocyte biological activity by hCG, according to our present preliminary findings, the presence of hCG apparently might play a causative role in OHSS, probably by inhibiting SOCS-1 mRNA expression and leading to IL-2 dominance with the consequent activation of the inflammatory response. Here, SOCS1 is linked to ovarian hyperstimulation syndrome.