Spontaneous forms of OHSS may occur, but these are very rare and always reported during pregnancy.

The pathophysiology ofOHSS remains poorly understood, and there is no reliable test to predict which patients will develop severe OHSS. Human

chorionic gonadotropin (hCG) is thought to play a crucial role in the devel-

ulating hormone (FSH) receptor could be an essential prerequisite in the

development of spontaneous OHSS and could explain why symptoms in

spontaneous cases of OHSS appear later than in iatrogenic OHSS, in which

follicular recruitment and enlargement occur during the ovarian stimulation

with exogenous FSH. Smits et aL described a mutation in the FSH receptor gene in a patient presenting spontaneous OHSS during each of her four

etiologicalroleinthedevelopmentofOHSS.Thedataavailablesofar supportthenotionthatOHSSisaconsequenceofmultiplecorpora!urea formationassociatedwithactiveangiogenesisandincreasedcapillary permeability.