Ovarian Hyperstimulation syndrome It is an iatrogenic complication of ovulation induction with exogenous gonadotropins and clomiphene-induced cycles Charecteristic feature of OHSS is an increase in capillary permeability resulting in fluid shift from intravascular to extravascular spaces Mechanism of Action Probably mediated by increased ovarian secretion of vasoactive substances including Vascular endothelial growth factor , elements of Renin-Angiotensin system and other cytokines Risk factors Young age, low body weight, PCOS, higher doses of gonadotropins and previous episodes of hyperstimulation Mild illness Charecterised by Ovarian enlargement, lower abdominal discomfo, mild nausea and vomiting, diarrhea and abdominal discomfo. Managed by outpatient basis with analgesics and bedrest; monitored by daily weight checkup, urinary frequency, clinical examination to detect ascites, lab tests of hematocrit, electrolytes and serum creatinine Serious illness Characterised by severe pain, rapid weight gain, tense ascites, hemodynamic instability, respiratory diffiulty, progressive oliguria leadng to renal failure, ovarian rupture and thromboembolic phenomenon Hospitalization and treated according to symptoms Ref: Clinical Gynecologic Endocrinology and Infeility; Eigth Edition; Chapter 31