Ovarian Hyperstimulation SyndromeOHSS is a medical complication that is both completely iatrogenic and unique to stimulatory infeility treatment.Its symptoms are the result of ovarian enlargement and fragility, extravascular fluid accumulation, and intravascular volume depletion.Proposed mechanisms for the characteristic fluid shifts that accompany OHSS include increased protein-rich fluid secretion from the stimulated ovaries, increased renin and prorenin within follicular fluid, and increased capillary permeability mediated by angiotensin. Vascular endothelial growth factor (VEGF), whose expression in granulosa cells and serum is augmented by hCG, and a variety of other inflammatory cytokines have been implicated in the pathogenesis of this disease.Reference: Novak's Gynecology; 14th edition; Chapter 32; Infeility and Assisted Reproductive Technology