CXCL8 and Infertility: Interestingly, the levels of both follicular IL-8 and IL-18 increased as follicles grew (adjusted for age and cause of infertility r = 40.2 pg/mL, P = 0.005, and r = 1  3.1 pg/mL for every additional millimeter in diameter, P = 0.022, resp).