Orvieto R1, Schwartz A, Bar-Hava I, Abir R, Ashkenazi J, La-Marca A, Ben-Rafael Z. Abstract PROBLEM: To aim of the study was to investigate whether controlled ovarian hyperstimulation (COH) causes endothelial activation and whether there is a correlation between endothelial activation and serum sex-steroid levels. METHOD OF STUDY: The study population consisted of 14 consecutive patients undergoing our routine IVF long gonadotropin-releasing hormone-analog protocol. Blood was drawn three times during the COH cycle: (1) day when adequate suppression was obtained (Day-S); (2) on the day of or the day prior to hCG administration (Day-hCG); and (3) on the day of ovum pick-up (Day-OPU). The levels of sex steroids and plasma soluble endothelial (E)-selectin were compared among the time points. Soluble E-selectin was measured with a commercial sandwich enzyme-linked immunosorbent assay. RESULTS: Soluble E-selectin levels were significantly higher on Day-OPU than Day-S and Day-hCG, whereas no difference was observed between Day-hCG and Day-S. No significant correlations were found between soluble E-selectin level and patient age, number of gonadotropin ampoules used, number of oocytes retrieved, or serum estradiol, progesterone and human chorionic gonadotropin levels. CONCLUSIONS: Human chorionic gonadotropin administration leads to endothelial activation regardless of the degree of ovarian response. Further studies are required to elucidate the relationship between COH and endothelial activation. These findings may lead to new strategies for predicting and preventing complications of COH, such as severe ovarian hyperstimulation syndrome.