On day 17, the subnuclear vacuoles have lined up at the basement membrane, creating the look of
On day 18, both subnuclear and supranuclear vacuoles are seen.
Day 18 or day 19 endometrium may mimic day 16 since there are variable numbers of subnuclear vacuoles. However, day 18 endometrium should contain some supranuclear vacuoles. In contrast to day 16, day 18 endometrium should not exhibit mitotic activity and the epithelial cells are less pseudostratified with smaller and more rounded nuclei.
Day 17 exhibits the even row of subnuclear vacuoles in greater than 50% of glands. Mitotic figures are largely absent.
On day 18, some of the subnuclear vacuoles have migrated to a supranuclear position, thus, both subnuclear and supranuclear vacuoles are seen.
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.