Immunohistochemical localisation of indoleamine 2,3-dioxygenase was studied in order to better understand the pathophysiology of placenta accreta spectrum. In the decidua staining for indoleamine 2,3-dioxygenase was found in the glandular epithelium with some additional positive cells. Extravillous cytotrophoblast invasion was present in the myometrium which was not covered by the decidual tissue whereas myometrial invasion of cytotrophoblasts was absent where this tissue lay deep to decidua. These results suggest that indoleamine 2,3-dioxygenase expression in the decidua may normally control trophoblast invasion and absence of its expression where decidua is absent may be involved in the pathogenesis of the over-invaded placenta.

We are grateful to the Grant-in-Aid for Scientific Research (17K11238), Japan Society for the Promotion of Science for financial support.