Table 1.

Described causal factors for ovarian hyperstimulation syndrome (OHSS)

Estradiol	Estradiol level is a reliable predictor of OHSS during ART [5]
	OHSS can occur despite low estradiol levels [10]
	High estradiol concentrations are not sufficient to induce OHSS [6]
	Currently considered a mere marker of granulose activity [11]
hCG	Fundamental for triggering OHSS
	hCG alone is not sufficient to induce OHSS [4]
Interleukins	Some interleukins are associated with OHSS, and elevated concentrations are associated with increased vascular permeability, hemoconcentration, elevated plasma estradiol concentration, and inhibition of hepatic albumin production [12]
Renin-angiotensin system	There is a direct correlation between plasma renin activity and the severity of OHSS [13]
	All hypovolemic conditions are associated with a secondary reactive hyperaldosteronism via renin-angiotensin cascade activation [17]
	Renin-angiotensin system activation is probably the effect and not the cause of OHSS
VEGF	VEGF expression is associated with OHSS increased vascular permeability [18]
	VEGF levels are elevated during ovarian stimulation with exogenous FSH, which is enhanced after hCG administration [19, 20]