Understanding ovarian hyperstimulation syndrome.

The ovarian hyperstimulation syndrome (OHSS) is a potentially life-threatening complication of ovarian stimulation treatments. Severe forms are characterized by a massive ovarian enlargement with the formation of multiple ovarian cysts associated with extravascular fluid shifts resulting in the development of ascites, pleural and/or pericardial effusion. The pathophysiology of the syndrome has not been completely elucidated yet. The vascular fluid leakage is thought to result from an increased capillary permeability of mesothelial surfaces under the action of one or several vasoactive ovarian factor(s) produced by the multiple corpora lutea. The paper focuses on the recent identification of mutations in the FSH receptor gene that display an increased sensitivity to hCG and are responsible for the development of spontaneous OHSS occurring during pregnancy. These findings have shed light for the first time on the molecular basis of the pathophysiology of the spontaneous form of the syndrome. As spontaneous and iatrogenic OHSS share similar pathophysiological sequences including massive recruitment and growth of ovarian follicles, extensive luteinization provoked by hCG, and oversecretion of vasogenic molecules by the corpora lutea, they have also opened new research perspectives for the understanding of the much more frequent iatrogenic OHSS.