[Differentiation of extravillous trophoblast during normal pregnancy]

The implantation site in 25 pregnant uteri was studied morphologically and immunohistochemically to clarify the developmental process of extravillous trophoblasts (EVTs). 1. Dense trophoblastic invasion of the decidua was observed. Multinuclear trophoblasts appeared in the deciduo-muscular junction from the 10th week. Trophoblasts infiltrated decidual vessel walls, where extensive perivascular degeneration existed. EVTs may be indispensable for construction of the placenta. 2. In villous trophoblasts (VTs) the location of hCG and hPL was limited to multinuclear cells, whereas in EVTs hCG was present in a few mononuclear cells and hPL was observed in most mononuclear and multinuclear cells. The immunoreactivity of trophoblast-related monoclonal antibodies also differed: neither anti-Tropl (reactive with cytotrophoblasts (CTs)) nor NDOG1 (reactive with syncytiotrophoblasts (STs)) was reactive with EVTs. 3. The absence of hCG and hPL in mononuclear trophoblasts of the cell column indicates that EVTs differentiate after invading the decidua. Kurman et al. proposed the term intermediate trophoblast, indicating cells in transition from CTs to STs and EVTs, and this is based on the concept that the developmental processes of EVTs and VTs are identical. But the results of this study suggested an independent developmental process for EVTs and therefore it seemed that the term intermediate trophoblast should not be employed for EVTs.