PAEP (Progesterone-associated endometrial protein, glycodelin, PEG, PP14) is a glycoprotein belonging to lipocalin structural superfamily. It shares a sequence homology to beta-lactoglobulins containing a retinol-binding motif and it is mainly produced by secretory and decidualized endometrium in women and by seminal vesicle epithelium in men (1). PAEP function is not clearly understood. However, glycosylated version of PAEP (GdA) has been associated to contraceptive and immunosuppressive activities during reproduction. PAEP is the main protein produced by secretory endometrium during mid-luteal phase of the menstrual cycle and during the first semester of pregnancy. Therefore, PAEP has been linked as an ideal biomarker of endometrial activity and function for in vitro fertilization treated women (2).