We previously demonstrated that the human endometrium synthesizes and secretes a specific protein designated “Progestagen-associated Endometrial Protein” or PEP. This work was undertaken to determine luteal phase levels of PEP in serum of cycling women with histologic evidence ofadequate endometrium (endometrium in phase) or inadequate endometrium (endometrium out of phase by 3-4 days). The results provide a normative curve with 95% confidence limits for serum PEP concentrations vs normalized cycle day in women with adequate endometrium (judged by histologic endometrial dating), and indicate that the PEP concentration increases exponentially after day 22, with a mean doubling time of 2.9511.60 (mean±SD) days (based on serial data from 13 women). More importantly, the proportion of serum PEP values falling outside of the 95% confidence limits was significantly greater (p<0.001) in women with inadequate endometrium (83%) than in women with adequate endometrium (16%). Therefore, determination of PEP in serum, rather than the more invasive endometrial biopsy examination, may serve as a method of choice for evaluating endometrial adequacy in infertile women.
