Immunohistochemical expression of endometrial proteins and pregnancy outcome in frozen embryo replacement cycles

The expression of two endometrial proteins, pregnancy-associated endometrial alpha-2 globulin (alpha-2 PEG) and 24K protein, was examined immunohistochemically in an attempt to identify a marker or a pattern which would predict subsequent implantation. Patients who had undergone in-vitro fertilization cycles and had at least three frozen embryos were recruited into the study. They received two cycles of hormone replacement therapy. The first was a monitored cycle in which dated endometrial biopsies were taken for immunohistochemical assessment using monoclonal antibodies to alpha-2 PEG and 24K protein and also for standard histological dating. In the second cycle, the frozen-thawed embryos were replaced. The results of the monitored cycle were then correlated with the pregnancy outcome in the transfer cycle. Ten patients conceived, of whom eight had a pattern of low immunohistochemical staining of alpha-2 PEG and high immunohistochemical staining of 24K. In the 15 patients who did not conceive, four had the same endometrial protein pattern (P less than 0.05). In the 13 specimens classified as histologically in phase, 10 (71%) showed incompatible protein expression. We conclude that the pattern of expression of the endometrial proteins alpha-2 PEG and 24 K may be potentially useful to indicate a receptive endometrium. Immunohistochemistry may yield information on endometrial development which is not apparent from routine histological assessment.