Figure 3. Pathogenesis of low follicle-to-oocyte index (FOI). Reprint from Alviggi et al. Understanding Ovarian Hypo-Response to Exogenous Gonadotropin in Ovarian Stimulation and Its New Proposed Marker- The Follicle-To-Oocyte (FOI) Index. Front Endocrinol. 2018; 9:589. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).