Tissue samples were obtained from each placenta — one roll from the chorioamniotic membranes and one from the umbilical cord. Two sections were taken from both the chorionic and basal plates. Tissues were formalin-fixed and embedded in paraffin. Five-micrometer-thick sections of tissue blocks were stained with hematoxylin and eosin, and the slides were examined by perinatal pathologists who were masked to the clinical outcomes.
Histopathological changes of the placenta were defined according to the diagnostic criteria proposed by the Perinatal Section of the Society for Pediatric Pathology [156 (link)]. Histologic features associated with acute inflammation are acute subchorionitis, acute histologic chorioamnionitis (maternal response), and funisitis/acute chorionic vasculitis (fetal response). The definition and staging of acute histologic chorioamnionitis and acute funisitis are described below:

Placental histologic features consistent with acute inflammation (maternal response) were diagnosed based on the presence of inflammatory cells in the chorionic plate and/or in the chorioamniotic membranes [156 (link)].

Stage 1 (acute subchorionitis/acute chorionitis): accumulation of neutrophils in the subchorionic zone and/or in the chorionic trophoblast layer of the extraplacental membranes.

Stage 2 (acute chorioamnionitis): more than a few scattered neutrophils in the chorionic plate and membranous connective tissues and/or in the amnion.

Stage 3 (necrotizing chorioamnionitis): marked neutrophilic infiltrate with degenerating neutrophils (karyorrhexis), thickened eosinophilic amniotic basement membrane, and focal amniotic epithelial necrosis.

Acute funisitis was diagnosed by the presence of neutrophils in the wall of the umbilical vessels and/or the Wharton’s jelly, also using previously reported criteria [98 (link), 154 (link), 156 (link), 157 (link), 218 (link)–220 (link)].

Stage 1 (acute chorionic vasculitis/umbilical phlebitis/chorionic vasculitis): neutrophils are identified in the wall of any chorionic plate vessel or in the umbilical vein (few neutrophils are usually present in the Wharton’s jelly, but without aggregates or concentric bands of inflammatory cells).

Stage 2 (umbilical arteritis): neutrophils are seen in one or both of the umbilical arteries and/or in the umbilical vein.

Stage 3 (necrotizing funisitis): presence of neutrophils, cellular debris, and/or mineralization in a concentric band, ring, or halo around one or more of the umbilical vessels.