SPDL1 and Infertility: Increased serum levels of sPD-L1 were detected in patients with endometriosis-related infertility, and more precisely the levels were nearly twice higher compared to control (19.33 pg/mL, 14.47-49.77 vs. 10.45 pg/mL, 5.48-14.40; p < 0.0001).