Ovarian hyperstimulation is an assisted reproductive technology in which fertility medications are used to induce the ovaries to grow multiple follicles and eggs in a single cycle. In addition to the woman having more eggs released than normal (usually one egg per menstrual cycle), she experiences much higher hormone levels, particularly estrogen released from the growing follicles. In some cases, the supraphysiologic levels of hormones may trigger an exaggerated response, resulting in ovarian hyperstimulation syndrome. The syndrome has a broad spectrum of clinical features ranging from a mild illness needing only close observation to a severe illness with cardiovascular collapse requiring hospitalization and intensive care treatment.