Fig. 2

Histopathology of the progression of acute histological chorioamnionitis (HCA). Hematoxylin and eosin-stained placental tissue sections showed as follows: (A) Control group; (B) Stage 1; (C) Stage 2; (D) Stage 3. Diagnosis of acute HCA according to our hospital criteria: The number of neutrophils per field was ≥ 5 at per high-power field (HPF) (magnification, ×200). Some neutrophils are found in the decidua, the membrane trophoblast of the chorion, the connective tissue of the chorion and the amnion (the insets of panels, magnification, ×400), with the arrow indicating the outward to inward infiltration of neutrophils into the placenta (A-D)