This study demonstrates that the mode of ovulation triggering significantly affects mRNA expression of proteins that have been suggested to participate in the development of OHSS, such as VEGF and inhibin beta, as well as expression of important enzymes in the process of steroidogenesis, such as CYP19A1, CYP11 and 3 beta-hydroxysteroid-dehydrogenase, and expression of FSHR and amphiregulin. This evidence concerns the gene CYP19A1 and ovarian hyperstimulation syndrome.