1) Ovarian hyperstimulation syndrome (OHSS) is a condition characterized by ovarian enlargement and fluid accumulation in the abdomen and sometimes lungs, due to controlled ovarian hyperstimulation for fertility treatments. 2) Risk factors include younger age, lower weight, use of gonadotropins like hMG for fertility treatments, high estrogen levels, and pregnancy. 3) Symptoms range from mild abdominal bloating to severe cases involving kidney failure. Prevention focuses on modifying fertility drug protocols and cycles based on estrogen level monitoring.