Ovarian stimulation with gonadotropin-releasing hormone (GnRH) antagonist co-treatment can provide live-birth rates comparable to those achieved with the long GnRH agonist protocol, and has advantages in terms of tolerability and safety. The most serious complication of ovarian stimulation for in vitro fertilization (IVF) is the ovarian hyperstimulation syndrome (OHSS), a rare but potentially life-threatening condition. OHSS is characterized by a cystic enlargement of the ovaries and an acute fluid shift, which may result in ascites, pleural effusions, pericardial effusion, and even generalized edema. Human chorionic gonadotropin (hCG), either exogenous or endogenous, is thought to play a crucial role in the development of the syndrome. In a GnRH agonist protocol, it was demonstrated that the administration of low dosages of hCG can be successfully applied in patients undergoing assisted reproduction technology (ART) to substitute for recombinant FSH in the final days of ovarian stimulation.