Increased levels of estrogen and pregnenolone in follicular fluid may affect follicle development in PCOS patients, and the mechanism may be related to HSD17B1, CYP19A1 and CYP11A1 expression change in FF exosomes, which encode enzyme-induced abnormalities in steroidogenesis. The gene discussed is CYP19A1; the disease is polycystic ovary syndrome.