Proliferative phase - straight/edema/coiled
Early secretory phase (POD 2-5)
    2: Uniform subnuclear vacuolization (≥50%),
        pseudostratification, frequent mitoses
    3: subnuclear vacuole+, nuclear uniformity, scattered mitoses
    4: luminal vacuole+, rare mitoses
    5: infrequent vacuole, secretion
Midsecretory phase (POD 6-8): no vacuole, no decidua
    6: prominent secretion
　7: early stromal edema
　8: maximal stromal adema
Late secretory phase (POD 9-14)
　9: spiral artery prominent
　10: periarterial predecidua
　11: islands of predecidua
　12: coalescent predecidua
　13: confluent decidua, granulocytes prominent
　14: extravasation
Menstruation - Crumbing of stroma, thrombi

Considering as out-of-phase a delay of 3 days or more.
Recent study suggests that simple histological evaluation is
not a valid measure of the quality of luteal function or endometrial receptivity.
Would be useful to exclude neoplasm or infection.