Presence of fetal intervillous cells in a case of chronic placental inflammation.

Chronic Histiocytic Intervillositis (CHI) is a rare and severe histological entity. We explored the origin of the intervillous cells with a Fluorescence In Situ Hybridization (FISH) XY probe on cases concerned by an intervillositis diagnosed between 2014 and 2023 involving male fetuses, focusing on cases with fetal complications and/or high-grade CHI. Six cases showed maternal intervillous cells, in accordance with the hypothesis of an allograft rejection reaction. One case showed a predominance of fetal intervillous cells. We suggest that it could be an excess of fetal microchimerism, possibly exacerbated by trophoblast damage and excessive inflammation in placenta.