Grade II (moderate OHSS) is characterized by distinct ovarian cysts (ovary size 8-10 cm), accompanied by abdominal pain and tension, nausea, vomiting, diarrhea.
Grade III (severe OHSS) is characterized by enlarged cystic ovaries (ovary size >10 cm), accompanied by ascites and occasionally hydrothorax. Abdominal tension and pain may be severe. Pronounced hydrothorax together with an abdominal cavity filled with cysts and fluid elevating the diaphragm, may cause severe breathing difficulties. Large quantities of fluid inside the cysts and in the peritoneal and pleural cavities cause hemoconcentration and increased blood viscosity. In rare cases, the syndrome may further be complicated by the occurrence of thromboembolic phenomena.