SEM at D4P showing gland variability between samples from women during a natural cycle. (A) The glands are raised on circular hillocks with large, slit-like openings and demonstrates an out-of-phase glandular appearance indicative of E2 stimulation alone or insufficient P4 exposure. Scale bar = 0.1 mm. (B) Epithelium of normal appearance displaying numerous flattened glands with small, rounded openings. Scale bar = 0.1 mm.