Cases of sOHSS together with its possible underlying mechanisms have been reported, and include the cross-reactivity of the FSH receptor (FSHR) to a pregnancy- or hypothyroidism-induced elevation of hCG, in response to TSH in which the specific β-subunits are similar to that of FSH [5-7], activating mutations of the FSHR [5-7], or hypergonadotropinemia caused by gonadotropin-producing pituitary adenomas [8-26]. Here, FSHR is linked to pituitary gland adenoma.