Peripheral arterial vasodilation hypothesis: a new insight into the pathogenesis of ovarian hyperstimulation syndrome

Ovarian hyperstimulation syndrome (OHSS) is a serious complication of ovula tion induction which, at present, is being studied increasingly because of its frequent occurrence as a result of the growing number of in-vitro ferti lization (IVF) programmes. The anatomical changes involving enlargement of the ovaries and increased capillary permeability leading to acute fluid shi ft have been traditionally proposed to explain the different clinical featu res observed in OHSS. Recent work from our group, however, has shown that t he pathogenesis of severe OHSS is more complex than currently understood an d that marked peripheral arteriolar vasodilation is a major event in the de velopment of the syndrome. Peripheral vasodilation may, in its turn, alter microvascular haemodynamics and permeability, This leads to a circulatory d ysfunction with marked homeostatic activation of endogenous vasoactive syst ems having vasoconstrictor and sodium- and water-retaining activities. In t his way, sodium and water retention would be a cause rather than a conseque nce of ascites Formation in severe OHSS. This report analyses current conce pts on body fluid regulation as well as neurohormonal and haemodynamic stud ies both in patients with severe OHSS and asymptomatic NF women, integratin g their findings into the present knowledge of the pathogenesis of the synd rome. Therapeutic implications are discussed.