Day 20-21: Luminal secretions peaks at day 20 and though not shown here, glands may be distended with secretions.
For day 20 and 21 endometrium, the glands have scattered secretory vacuoles. The stromal changes take precedence starting at day 20. Note the edematous stroma. The stroma cells have very scant cytoplasm and are widely spaced, thus, taking on a
Stromal edema which starts to develop during early secretory phase (day 17 and 18) quickly peaks at day 22. The glands begin to increase in complexity.
Note again the stroma edema with scattered subnuclear vacuoles.
The loss of secretory vacuoles by day 19 marks the end of the early secretory phase and the beginning of the mid phase. From this point onward, stromal changes will be the determinant in dating. Although there will be scattered subnuclear and supranuclear vacuoles throughout the mid to late secretory phase, they will never be as prominent as in day 16-18.
Note that luminal secretions peak at day 20 and continue to be present throughout the secretory phase. Glands will display secretory exhaustion. During this time, the stroma becomes edematous and stroma edema peaks at day 22.
Luminal secretions (which decrease at the end of the mid-secretory phase) and edematous stroma (which increase at the end of the mid-secretory phase) are the two key features of day 20 through day 22.
1 Mazur MT, Kurman RJ. Diagnosis of Endometrial Biopsies and Curettings. New York, NY: Springer; 2005: 12-19.
2 Nucci MR, Oliva Esther. Gynecologic Pathology: Foundations in Diagnostic Pathology. Philadelphia, PA: Elsevier: 2009: 200.