We hypothesised that changes in the ratios of endometrial versus serum levels of these two molecules in PCOS patients could lead to alterations in the stoichiometry of the OPN-CD44 adhesion complex at the endometrial surface, thus promoting the saturation of OPN and CD44 receptors on the surface of the blastocyst by secreted molecules. This evidence concerns the gene SPP1 and polycystic ovary syndrome.