At day 22, stromal edema reaches its maximum. There is the first hint of periarterial

Note the stromal edema, early predecidualization around a vessel (upper right) and plentiful luminal secretions in this day 22 endometrium.

At day 22, stromal edema reaches its peak. There is the first hint of predecidual cuffing around the vessels. Luminal secretions and scattered secretory vacuoles may be present.

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.