OHSS is a complication caused by the significantly increased hormone level in the body after hormonal stimulation of ovulation. The puncture of the oocyte leads to ovarian hyperfunction, accompanied by enlarged ovaries and ovarian cysts. In severe cases, the increased hormone level may cause very painful cystic swelling of the ovaries, associated with hyperpermeability of the capillaries and fluid accumulation in the abdomen, as well as alterations in blood pressure and density.