Ovarian hyperstimuation syndrome (OHSS) can be a life-threatening complication of ovulation induction or ovarian stimulation. The enlarged, stimulated ovaries produce vasoactive substances which act on endothelial cells to increase wall permeability, which results in the third spacing of fluid (ascites, pleural effusions) and haemoconcetration. As a result, these patients are at increased risk for thromboembolic events. 

OHSS patients are also at much greater risk of ovarian torsion. Because both ovaries are already enlarged in OHSS, the key is to look for asymmetric ovarian enlargement with stromal edema and thickened parenchyma in the setting of severe abdominal pain.