Late luteal phase progestogen-dependent endometrial protein levels in women with in-phase biopsies--can low levels predict a subfertile group?

A group of infertile women who had luteal phase defects (LPD), but in whom follicular maturation was deemed normal, were treated with progesterone until the endometrial biopsy was corrected. At the time the corrected biopsy was obtained, serum was taken and the progestogen-dependent endometrial protein (PEP) concentration was determined. Serum PEP concentration in patients who successfully conceived was 102.5 +/- 62.6% units/mL, while PEP concentrations in patients who failed to conceive were 57.9 +/- 34.4% (P = .003). In patients whose PEP value was more than two standard deviations below the corresponding mean control PEP, pregnancy was achieved in 6/17 (35.3%). The conception rate was significantly greater (25/35, 71.4%) in patients with values higher than this. Thus, the PEP concentration in serum may identify a group of patients with persistent LPD despite apparent normalization of the morphology of late secretory phase endometrium, which might explain some cases of cryptic, unexplained infertility.