OHSS is a medical complication that is 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 Vascular endothelial growth factor , 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 This tends to be more severe with multiple gestation Clinical feature:- Abdominal distension, Abdominal pain, Nausea and vomiting. Management : Intravascular fluid intake to replenish the volume Symptomatic treatment , like tapping of the ascites and pleural effusion